Report of the Eclipse Expedition to Caroline Island, May 1883. (1884)

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S O L A R E C L I P S E , M A Y 6,1883. 61 OBSERVATIONS O F SOLAK K A D I A T I O N . In iulditiou to tlic ordiu.iry meteorological observations, a series of observations ot solar radiation was planned. Tbeir object was primaiily to furnisli a basis of comparison tor the obser- vations made with the same instruments during the eclipse, but they also furnish a means of deter- mining the intensity of the solar heat on the days upon which the readings were made. They are of especial interest on account of the position of the observing station. Two kinds of instruments were employed, furnished through the kindness of the Chief Signal Officer. 1. ConjugaU thermometers of the MMS,it-I>iiYYpattern.—These were made especially for the expe- dition by Messrs. J . & H . J . G E E E N , New York, and consisted of a black and bright bulb thei- mometer, each inclosed in a vacuum,* the mclosure being spherical in shape where it surrounded the bulb of the thermometer. The diameter of the inclosure was 2.15 inches, the bulb being cen- trally situated within it. The thermometers themselves were of the ordinary pattern with laige graduations on the Fahrenheit scale. Instruments of this class are sometimes made with maxi- mum thermometers, but this is very inconvenient where readings are to be made at stated times during the day. Two pairs of instruments were used, numbered 1, 2,3, and 4 by the makers. 2. ^ l O L L E ' s conjugate btilbs.—These consisted ot two hollow copper spheres 4.04 inches m diam- eter, one blackened, the other gilt. I n each was placed a thermometer graduated to half degrees centigrade, with its bulb blackened and located centrally within the sphere.* I n addition to these special instruments, two ordinary thermometers. G R E E N 113G and 1137, were exposed in the sun, with the bulb of the latter blackened. The diftercnco of the readings of these thermometers is an approximate measure of the solar radiation, but the result does not have the value of either of the other methods. The conjugate thermometers weic mounted upon brass supports 7 inches high, and each i>air of suiiports was screwed to a board painted black. The boards were placed upon the gioivid in an open grassy spot selected with espeual care for these observations. The thermometers w ere nearly horizontal, but sufficiently inchned, bulb dowu,ward, to secure an unbroken column of mer- cury. T h e inclosures of the thermometers constituting a pair faced each other at a distance of several inches, the white bulb toward the east. The board containing the instruments was turned at frequent intervals during the day in order that they might have approximately the same posi- tion with regard to the sun. The V I O L L E bulbs were mounted each upon a wooden stand 10 inches above the ground, with the stems of the thermometers projecting horizoutally toward the south or opposite the sun. The ordinary thermometers were exposed horizontally, each attached by a brass support to the corresponding thermometer of the conjugate pair, and situated a couple inches above it. The instruments thus placed were in a favorable position for the desired observations, which were nlade hourly or oftener upon every clear day during the stay upon Caroline Island, beginning with April 27. *The instruments devised by Man6-Davy are described m the Bulletin Moiisiiol do I'Dbs Phys Central de Mont- aouris, 1873, p 80, and 1874, pp 134 and 189 *A f u l l description of those instruments, w i t h the fonuula for reducing the readings, is'given in " Sur laR.idiation Solairo," bV'M J ViOLLt, Pans, 1879 

MEMOIRS o r TLlli NATIONAL ACADEMY O F S C I E N C E S . 62 The tollowiiig table coutaius tbo obscrvatiouh in detail: FRIDAY, A l ' K l L 2T Conjugate tlioiiiioiiioteia V i O L L K ' b bulbs Oriliiidiv tboruioiiiotors Ruiii.iiku Tiiiio UUok lil.iLk Gill. lilacU Biifllit No 7 U No 751 No 1157 No 1150 No 4 No 3 No 2 No 1 A M Sun jiist outcniiK clontl 7 00 94 3 85 7 Sj)iinkling , bulbs wut 8 00 81 2 78 G Sun cloiir 105 1 95 0 88 2 9 00 130 0 89 2 80 0 Sun behind clouds 10 00 110 1 90 1 Sun behind t h i n c i i sti cloudu 108 7 95 7 90 0 11 00 134 0 98 0 93 0 Do 12 00 144 C 115 7 42 4 54 8 r M 40 8 3-1 8 101 1 95 3 Sun clear 12 10 142 9 144 9 114 9 112 8 Do 146 3 115 7 113 8 41 3 34 9 105 5 '9fi 2 12 12 144 7 102 0 90 5 Do 12 15 144 9 14G 9 110 0 114 2 41 2 35 1 37 8 102 0 95 0 Sun bohiiul thin oir str clouds. 1 00 141 7 144 5 114 5 112 3 42 5 Do 1J9 8 113 4 111 0 42 7 38 1 100 8 94 8 2 00 H8 7 100 3 95 5 Do 3 00 m 0 13<J 4 110 1 108 3 42.!) .57 7 104 3 41 2 30 4 95 0 89 5 Do 4 00 12() 9 U() 9 105 7 80 8 83 4 ^83 C 28 4 28 8 8.1 2 82 7 Sun bcliiiid clouds 5 00 SO 2 Smmuauj - P o o r il.ay Sim clc.ir at 9 00 .1 i.> aud 12 10 to 12 15 i . ui. ouly SATURDAY, APRIL 28 Coiijugiitc tlioriuoiiiotcrs VlOLIl.'b bulbs Oriliiuiry tliuriuomoturs Reni.irks Tunc Ulaok Biigbt 151.iok Gilt Hl.ick Blight - No .751 No 1157 No 1130 No 742 No 4 No 3 No 2 No 1 A M 35 I 95 5 87 n Sun in thin ba/e 7 40 123 8 99 7 38 8 95 6 34 8 32 1 97 2 89 0 - Sun emerging fioiu cloud 8 00 114 0 115 3 94 9 90 .5 Sun clear 139 5 108 1 108 0 40 8 30 4 97 4 9 00 137 0 100 5 92 0 Do 1.5G 5 139 2 108 9 108 5 41 1 30 0 9 50 37 2 100 0 92 0 Do 9 55 157 C 140 5 109 8 109 4 41 8 109 2 41 0 30 3 100 7 91 4 Do 10 00 137 3 140 0 109 9 93 8 Do 136 4 140 2 110 1 110 2 42 '1 .57 9 102 0 10 50 38 2 102 3 94 2 Do 10 35 1'58 0 141 8 111 1 111 1 43 0 115 7 43 8 38 7 102 5 94 3 Do 11 00 140 G 144 1 114 0 94 0 Do 140 1 143 2 113 9 114 3 43 4 38 C 101 0 11 30 44 4 39 2 105 0 96 2 Do 143 2 14C''2 115 0 114 9 12 00 1> M 40 5 40 4 10() 5 97 5 Do 12 30 147 0 14') 2 118 2 118 2 Do no 5 116 5 45 2 "39 7 104 0 90 8 1 00 14 5 2 143 9 90 0 Do 141 0 141 5 110 2 115 5 45 1 39 6 10.5 2 1 30 42 0 105 5 99 0 Sun bobind thin chuids 2 00 143 1 140 5 119 5 118 0 47 0 Sun clear, clouds iiiiuiediatoly 120 1 118 8 48 5 42 0 107 U 99 8 2 08 145 0 148 3 afterward 40 0 40 4 loe 2 97 7 Sun clear 2 15 145 9 148 5 118 0 117 8 118 8 117 0 45 1 39 8 105 2 90 8 Sun clear jnst before entering 2 22 148 5 150 2 cloud 109 8 109 0 40 9 30 7 105 2 95 5 Suu clear, b u t in clouds just bo- 2 30 133 6 135 8 fore and after 111 6 110 6 43 1 37 8 102 3 94 8 Suu behind t h i n clouds 3 00 137 8 139 9 92 2 154 G 137 8 109 0 108 8 41 5 30 8 99 5 Do 3 30 35 7 90 8 90 0 Sun clear 4 00 127 7 130 4 113 0* 104 5 .59 7 121 0 98 0 37 0 34 2 Do • 4 30 5 00 105 0 107 2 92 0 91 0 32 8 32 0 80 0 j 83 8 Sun j n s t euteiing cloud - Should be 103 0 Su^nraary - S u n clear 9 00 a n. to 2 00 p lu The p n, observations affected by passing clouds. Two maxima mdacated, at about 12 30 and 2 30 p. m 

S O L A R E C L I P S E , M A Y C, 1883. 63 SUNDAY, A P R I L 20. Conjugate theriuometers VIOLM;'S builds Oidinary thouuouicteis Time Black Bright Eeniaiks Black Gilt, Black Blight No 742 No 7r)l No 1137 No 1136 No 4 No 3 No 2 No 1. A M. 6 40 89 8 89 9 83.8 83 6 28 4 28 1 55 3 81 4 Sun in tliiu clouds 6 50 90 C 91 2 84 0 84 2 28 7 28 4 85 5 82 7 Suii 111 clouds , 6 55 101 8 103 7 88 7 88 5 31 0 29 5 89 5 84 5 Sun almost clear, clouds rollo^\ 7 48 124 5 -125 1 100 5 99 2 36 7 :i3 5 Sun in thin haze 7 54 126 6 125 9 100 9 100 5 37 9 34 3 Do 8 00 128 1 127 0 100 7 101 3 38 8 35 1 Do 8 30 131 7 130 3 103 3 103 0 38 6 35 4 Sun just entering cloud 8 40 131 7 130 5 101 5 104 2 38 8 35 4 Sun cle.ar 0 00 135 0 133 5 105 4 106 6 39 7 36 0 97 5 90 5 Do 9 20 138 5 130 3 1,07 2 108 7 40 5 30 6 100 3 92 4 Do 9 30 139 7 137 5 108 1 109 6 41 0 37 0 100 3 92 3 Sui. clear, but ]U8tout of clouds 9 35 140 8 138 7 108 9 110 2 41 4 37 4 101 2 93 3 Sun clear or in haze 10 00 144 2 142 7 111 9 112 8 43 1 38 9 104 0 95 0 Do 10 30 150 5 149 9 116 2 116 5 45 5 40 5 108 8 97 8 Sun just cntrt'ring cloud 11 00 142 0 142 5. 112 4 112 1 45 6 38 2 101 0 94 0 Sun clear 11 143 5 145 1 114 b 113 8 45 6 33 7 105 a 96 7 Do 11 30 144 0 146 b 115 7 114 4 45 6 39 9 105 5 97 5 Do 11 45 144 0 147 3 lib 0 114 8 45 6 39 5 107 0 it7 8 Do 12 00 143 2 146 2 115.8 115 0 45 5 39 9 106 8 98 0 Do P M 143 7 147 0 110 2 115 3 45 5 39 8 107 7 98 0 Do 12.15 12 30 144 0 147 0 116 9 116 0 45 5 40 2 106 5 98 0 Do , 1 03 147 7 149 2 119 1 118 7 46 5 41 1 108 2 100 0 Sun clear Max readings after clouds 1 30 141 0 140 7 115 6 114 9 46 0 39 5 105 7 98 0 Sun clear 2 10 138 0 139 8 115 1 114 2 46 0 39 7 101 0 96 0 Do 2 30 135 5 140 5 114 4 113 5 46 0 39 7 101 8 Ob 5 Do 3 00 139 0 137 9 112 2 112 0 4b 0 39 2 102 0 95 5 Do 3 30 1.K 0 133 0 109 8 109 0 45 9 i8 3 99 2 94 0 Do Siimmaiy —Tionbled by passing clouds t.hionghout the day, though gcnor.illy clear when reatlings were made MONDAY, APRIL 30 Conjugate thorniomoters V I O L M ' S bulbs Oidiii.ary tlicinioiiietci's Time Black Biiglit Remarks Black Gilt Black Bright No 742 No 751 No 1137. No 1136. No 4 No 3 No 2 No 1 7 111 8 92 9 33 6 31 2 88 2 '84 2 Sun clear 7 114 1 116 7 94 8 95 1 34 7 32 1 89 8 85 2 Do 7 121 8 121 7 98 9 97 8 36 2 33 2 92 4 8b 3 Sun cle.ar, cloudy 7 45-8 00 . i in 8 122 0 122 5 99 I 98 5 38 0 34 0 97 5 89 2 Do 8 134 0 134 9 »llb 5 *114 9 41 5 37 1 08 2 90 3 Do 8 135 1 13b 5 107 2 106 5 43 0 38 0 99 2 92 5 Do 9 138 2 139 5 109 5 108 3 43 9 38 9 101 7 92 5 Do 9 143 3 145 5 113 2 112 7 46 5 40 2 105 0 95 0 Do 10 00 99 3 100.8 92 9 92 1 33 6 33 8 86 0 85 0 Sun in heavj' clouds for ten miiin tcs bcforr 10 30 138 3 139 7 109 5 109 1 4) 8 :« 4 101 2 93 ? Sun clcflr , i.aiii diops on bulbs 10 45 147 0 145 9 113 7 114 8 46 2 40 6 108 7 98 2 Sun cle.ii 11.00 148.2 147 5 115.4 116 7 46 7 42 0 109 1 - 99 0 Do 11 30 148 8 149.0 117 2 11- 5 46 2 41 8 105 5 98 0 Do 11 45 147 9 149 0 117 2 117 3 45 4 40 8 109 3 99 5 Do 12 00 148 0 149 8 117 8 117 9 4b 5 41 9 110 0 100 5 Do P M. 12 15 147 3 149 2 117 8 117 3 45 5 40.5 109 4 99 8 Do 12 20 Instinments taken away on account of wind squall and expected ram Brougbt out at 2 00 p in 3 00 136 8 137 7 109 5 109 2 41 7 37 4 98 5 93 0 Sun clear 3.30 13J 1 1.14 2 107 2 10b 8 39 8 35 5 98 3 91 5 Do 4 00 129 1 129 8 104 M 103.9 39 5 35 9 97 5 90 5 Do 4 30 122 5 122 2 100 9 99 5 36 7 34 2 93 5 87 5 Do. 5 00 113 8 113.0 96 0 94 7 35.2 32 4 85 2 86 0 Do * Probably should bo 100 5, 104 9 Summary—Good weather, especially m p m 

64 MEMOIRS OP T H E NATIONAL A C A D E M Y OP SCIENCES. TUESDAY, MAY 1 Conjngate thermometers V i O L L E ' s bulbs Ordinary thcTmoinotors Time Black Bright Remarks Black Gilt Black. Blight No 742 No 751 No 1137 No 1136 No. 4 No 3 No 2 No 1 - A M f. 30 91 i 91 7 84 0 84 0 28 8 28 3 83 8 82 0 Sun clear, porhapa in haze C 35 96 7 97 8 -8T 9 86 2 30 2 29 1 85 2 82 5 Do f> 40 100 1 101 6 86 9 87 7 .11 2 29 7 8(> 5 8:1 0 Do fi 45 102 9 104 3 86 9 80 0 11 0 30 2 8() 7 83 5 Do fi '•.0 105 2 106 9 88 6 im 0 •U 2 30 5 87 2 83 5 Do f> 55 107 5 109 3 90 8 91 2 32 fi 30 7 83 5 83 8 Do 7 00 109 8 111 6 92 3 92 2 3't 5 31 3 89 2 84 5 Sun clear. 7 15 114 5 117 0 95 5 95 0 34 4 3J 0 90 5 85 2 Do 7 30 121 8 122 S 99-5 99 0 .17 5 34 1 ••2 2 87 0 Do 8 iO 129 2 130 5 104 8 105 0 40 8 36 5 98 0 92 0 Do 8 45 133 3 137 0 107 5 107 5 41 8 37 5 98 2 91 2 Do 9 00 "126 0 135 0 108 3 107 8 42 C 38 4 99 5 92 5 Do 9 ^0 13« 0 138.8 109 8 110 0 44 0 39 fi 101 2 94 0 Do 10 00 140 9 141 3 111 5 in 0 44 6 40 0 10! 0 95 0 Do 10 30 lif 5 143 9 112 5 115 0 44 8 V) 9 10.! .-> 96 0 Do 11 00 146 0 147 0 114 0 116 8 46.9 41 8 106 5 99 2 Do 12 00 147 9 149-3 114 0 117 5 47 2 41 6 106 5 . 99 3 Do 1* M 140 3 tl50 2 114 5 117 3 46 7 41 3 107 5 99 2 Do 21 00 00 144 2 145 0 112 2 115 5 4fi 2 40 7 106 2 97 0 Do 3 00 139 2 1.1b 5 108 5 111 5 45 4 40 3 102 (> 95 0 Sun behind thin cir str 3 40 132 5 129 8 103 2 107 7 43 0 38 7 99 5 92 b Do "Resei voir partly m shivde of the stem tProbablj the maMinuiii readingbofoic 1 00 p in , as thr colnmn was found broken at 2 00 p ni Summary —Obscivations in early a m wcro made frequently. U j i to .! 00 p m all leadings .are unusually good WEDNESDAY, MAY 2 Conjugate thcrmoniotcrs V O I L I F ' S bulbs Ordiuarj Ihcimomoters Tune Black Bright Remarks Bl.icK Oilt Bright No 742 No 751 No 1137 No 11.16 No 4 No 3 No 2 No 1 A M 6 30 90 2 91 0 83 5 84 0 28 0 28 2 83 3 82 0 Snu behind thin clouds 7 00 110 8 111 2 93 8 93 0 32 9 10 8 87 2 84 0 Sun clear 7 40 122 6 121 0 98 2 99 0 38 0 34 9 <)1 2 87 0 Do 8 00 l!l 2 127 5 102 8 102 7 40 t 36 5 94 -) 89 0 Do 8 30 127.9 124 9 102 8 102 8 39 a 36 5 98 2 91 0 .Sun cle.n, but just emerged from clouds 9 00 137 8 135 0 107 9 108 4 42 0 38 0 101 0 92.5 Sun clear, but emerged from clouds five minutes before 10 00 145 0 143 0 113 114 3 45 0 40 5 104 7 90 0 Sun clear 10 .10 146 9 144 8 115 115 2 45 5 40 8 10! 0 95 8 Do in 45 147 5 145 5 111 115 3 45 9 41 0 105 4 90 5 Do 11 00 148 2 147 0 116 116 2 46 3 41 3 106 0 97 0 Do 11 15 149 0 148 5 116 117 0 47 0 41 7 107 7 98 5 Do 11 30 148 9 149 3 116 116 8 46 9 41 7 109 2 98 5 Do 12 00 148 0 148 9 115 8 116 5 46 2 41 1 m, 0 97 7 Do P M 12 30 148 0 149 2 115 8 117 2 46 0 41 6 107 2 98 5 Do 1 00 147 4 149 2 116 2 117 8 47 9 42 6 109 0 98 5 Do 2 00 144 5 145 5 115 5 117 0 49 1 43 6 107 2 98 8 Do 2 30 141 7 141 0 114 0 114 8 47 8 42 7 104 5 97 5 Do 3 00 1.18 7 143 7 110 0 113 2 47 5 42 4 104 2 95 5 Do .! .!0 135 0 139 fi 107 2 109 4 44 8 40 4 102 8 94 0 Do 4 00 131 5 135 0 tll5 5 106 0 4! 9 39 6 101 0 92 5 Do. 4 30 124 5 127 0 102 5 100 8 40 0 36 8 97 4 88 5 Do 4 45 120 0 120 7 100 0 98 0 37 0 34 I 93 0 87 0 Do. 5 00 116 0 116 0 97 7 95 8 35 9 33.3 91 5 86 5 Do. * Bulb close to gr.ass blade / t Should be 105 5 Summary —Sky almost wholly clear after 9 00 a m. The p. m observations are especially good 

S O L A E E C L I P S E , MAY 0,1883 65 THURSDAY. MAY 3 Conjugate tlierinoiueteis VlOLLb'S bulbs Oidiuaiy tliciiiioiuctcia Tune I5Uck Blight Rciii.irks ]51.ick Gilt Black Blight No 742 No 751 No 1137 No 1130 No 4 No 3 No 2 No 1 A »I 7 00 100 8 lOG 6 91 0 90 4 3i 2 50 8 89 5 84 5 Sun L1C.II 7 50 114 '2 114 1 90 0 95 0 35 1 33 2 88 5 35 0 Sun p u t l y c l c . i r , iii clouds just befoiu 8 50 131 2 130 0 104 4 104 2 40 0 57 0 9b 2 39 8 Snu ble.li, in cloiuU .it 3 00 JL in 9 00 156 2 130 0 107 o 103 0 41 6 57 5 99 5 92 0 Sun )iitit cutciiiig cloud 10 30 14 5 b 142 2 112 0 113 5 43 b 53 7 104 0 90 0 Suu clcai 11 00 147 5 148 0 114 9 110 2 44 2 39 2 104 0 90 5 Do 11 50 140 7 147 9 114 5 115 0 44 5 39 5 105 5 97 0 Do 12 00 14b 9 143 7 115 1 lib 0 44 9 59 8 105 5 97 5 Do I* M 12 50 140 0 148 2 115 1 116 6 45 2 40 0 100 0 98 0 Do 1 00 140 0 148 1 115 5 117 0 45 9 40 5 107 5 93 0 Do 1 .50 147 5 147 1 116 0 110 9 46 2 41 0 100 5 93 7 Do 2 no 144 7 145 0 114 0 115 2 44 b 39 8 100 0 97 2 Do 2 50 140 8 141 0 111 0 112 6 45 0 39 1 105 0 90 0 Sun jiibt ciiteiiiig cloud Summujj—Sky not wholly clo.ii Obseivatious boloio 10 30 . i in and .iftoi 2 00 p in wcio iiitetlciod with by p.isbiiig cloudb Botwoou these timesrti,idingi> .lie ich.iblc No laduitiouobsoivatious woio uutdcMay 4 ou account of clouds SATURDAY, MAY 5 Conjugate thcrmomoteis V I O L L E ' S bulbs Ordinary thciniomclois Tune BKick Briglit Rciuaiks BKick Gilt Bl.ick Bright No 742 No 701 No 1137 No 1136 No 4 No 3 No 2 No 1 A M 3 30 129 2 120 3 105 5 101 2 56 4 33 4 92 2 88 0 Sun in haze 10 00 157 5 vl37 2 109 5 109 2 39 7 35 7 93 0 91 8 Sun deal 10 30 142 6 142 5 112 5 112 5 41 7 .57 2 99 8 93 2 Do 11 00 142 0 142 5 111 7 111 9 40 S 5b 5 100 8 95 7 Do 11 50 143 0 141 5 112 0 112 5 41 4 30 7 101 5 95 0 Do 12 00 143 0 144 0 112 0 115 0 41 1 50 5 102 5 95 0 Suu just out ot Lir t,ti clouds Summai i/ —Sky cloudy iieaily .ill day, but the low loadiugt. made aio ieli.ibIo " S Mib H O 9 

66 M E R I O I K S OF T H E N A T I O N A L A C A D E M Y O F S C I E N C E S . SUNDAY, MAY 6 Conjng.ite V I O L L E ' S bulbs Ordiiiaiy thcimoinotcis thoiiiiomcteis Time Rcmaiks Black Blight Bl.ick Gilt Black Blight No 5 No 1 No 742 No 751 No. 1137 No 1136 A M U 45 125 2 98 6 35 1 31 8 94 0 37 5 Sun cleai, but jiis>t cineigcd fiom clouds 9 57 157 0 105 1 33 3 34 8 95 2 89 2 Sun cleu 10 55 131 0 104 3 37 1 54 4 94 0 88 3 Sun cle.ii, <ii paitial eclipse !• M 12 55 121 0 99 35 35 5 94 2 90 0 Do 12 00 130 4 105 57 54 5 97 0 90 3 Do 1 02 130 3 103 59 55 5 98 5 91 7 Do 1 10 159 0 110 .59 36 0 93 2 91 5 Sun deal 1 30 139 0 110 59 56 I 93 8 91 8 Do 2 00 155 6 110 59 36 0 98 5 91 0 Do 2 50 155 0 109 40 .56 5 97 2 91 5 Sun jiist out of clinids 2 32 154 9 109 40 .56 5 99 2 91 3 Suu clc.ii Ma\' values bcfoie .igaiii ob- scnicd 2 45 158 2 103 9 40 3C 3 96 8 00 7 Sun dear 5 00 150 7 107 5 59 35 8 97 91 2 Do 3 10 154 5 105 7 38 35 3 95 90 0 Do 3 45 129 5 102 7 37 34 4 95 39 5 Sim behind thin clouds Cloudy at .1 00 p III 1.52 9 105 3 38 5 34 9 96 89 Siin clear 126 2 101 0 36 3 55 8 95 88 Sun in ha/c 122 3 101 0 56 1 35 4 92 87 Suu c l e u , butwholeiiky is hazy 117 2 93 5 54 3 32 6 91 86 Sun in hazo 110 2 94 0 52 9 31 4 33 8- Do 109 2 9.! 8 32 8 31 2 37 85 0 Do SuiiiiiMi!i —Cloudy until 9 43 a iii , and .it luteiv.il8jthioughoiit the day [SpocKil obseivatious iiuido fiom 10 00 ,1 m to 1 15 p m aie given below ] Special obset vations tn connection with sola) eclipse. J C IIAUOI.D, obbcivei SUNDAY, MAY 6 Ooiijiigate V i O L i L'S bulbs Oidin.uj tliciiuoiiieteis thcrmometeis Tmie Reiuaiks Black Bright Bl.ick Gilt Black Bright No 3 No 1 No 742 No 751 No 1137 No 1150 A M 10 00 137 5 106 0 38 5 35 0 97 0 Sun deal 10 05 158 5 106 5 59 5 55 5 98 0 Do 10 10 159 0 107 0 59 5 35 5 97 0 Do 10 15 138 0 107 0 59 0 55 5 97 0 Do 10 20 137 0 107 0 .59 0 55 5 97 0 Do 10 25 156 0 100 0 58 5 35 > 96 0 Do 10 50 135 0 105 5 58 0 55 0 95 0 Do 10 55 151 0 104 5 37 0 .54 5 94 0 ]5o 10 40 124 0 101 0 36 34 0 37 0 Sun ill cloud ' 10 45 113 5 96 0 35 32 0 90 0 Sun deal 10 50 115 5 97 0 55 52 0 91 5 Do 10 55 115 0 97 0 54 52 0 90 5 Do 11 00 115 0 96 0 33 .52 0 89 0 Do 11 05 lO'l 0 04 0 .52 51 5 88 0 Sun in cloud 11 10 101 5 92 0 31 50 5 3b 5 Do 11 15 100 0 90 0 30 30 0 35 5 Do 11 20 99 5 87 0 23 2.-1 5 84 0 Do 11 25 90 0 65 0 28 23 > 35 0 Sun cle.ai 11 50 86 0 83 0 27 28 0 32 0 Do 85 0 32 0 26 5 28 0 81 5 84 9 82 0 27 0 28 0 31 5 82 0 Total ])1i.isu (if eclipse Laiilciii used 82 0 27 0 28 0 82 0 11 38 32 0 82 0 27 0 29 0 82 0 

Fig. 19. CURVES OF BLACK AND BRIGHT BULB THERMOMETERS DURING ECLIPSE Tike. PM moo 10.15 10 30 1045 1100 1115 11 30 1145 1300 IStS 11 •30 12' '45 100 TIS[ \~10S' of -100° Black bulb freely oxposort Bright Sopointo obsorvatioiiH of blade balb o \^80' " " " bnght ' ? Denotes sun in Uonila at time of i-c iiliiig Other rcKluigs w(>r(i Boniotiuics iffoctPd by olouds provions to tlio obsei\attoii I 1 I I L _ 

S O L A R E C L I P S E , M A Y G, 1883 67 Special observations in connection with solar cclii^se—Continued SUNDAY, MAY 0—Continued Conjugate V i o i I p's bulbs Oidinary tliciniometcii Iboiiiioinctois Tunc h'cin 11 ks Black lliiglif HI ick Gilt I'.liok lliight No ! No 1 No 742 No 751 No 11 17 No 1116 A M U 40 82 0 81 0 27 0 27 o 82 0 81 5 Run cloai 11 45 82 0 81 0 27 0 2- 5 62 0 81 5 Sun III (loud 11 50 81 0 82 0 27 5 28 0 8! 0 82 0 Sun clt 11 11 55 as 0 84 0 28 5 28 5 84 5 ' 8! 0 Do 12 00 90 0 35 0 29 0 28 5 84 0 8! 0 Do 1 M 9! 0 8fi 0 20 -> 20 0 8') 0 8! 0 Do 12 05 12 10 <)9 0 b<) 0 oO 5 10 0 89 0 85 0 Snu m cloud 12 15 101 0 •to 0 !1 5 iO 5 90 0 80 0 Do 12 20 98 0 80 0 11 0 !0 5 85 0 b! 0 Do 12 25 109 0 94 0 !i 5 11 5 9! 0 87 0 Do 12 !0 11! 0 94 0 !4 0 12 0 ')2 0 87 0 Sun < leai 12 !5 120 5 100 0 !5 0 1! 0 94 0 89 0 Do 12 40 124 0 102 0 !6 5 14 0 9i 0 88 0 Sim III cloud 12 45 124 0 102 0 !(> 0 1! 5 95 0 89 0 Siin cic 11 12 50 110 0 105 0 !7 5 14 5 97 0 90 0 Do 12 55 1!2 0 106 0 !S 0 !5 0 06 0 90 5 Do 1 00 115 0 108 0 !9 0 15 5 08 5 91 0 Do 1 05 lid 0 110 0 10 0 1(, 0 101 0 92 0 Sun 111 cloud I 10 1 !7 0 109 0 40 0 ih 0 97 0 91 0 Sun clpai 1 15 1!') 0 110 5 40 0 3() 0 98 0 91 5 Do The detailed obbeivations show A\ith snlTicicnt completeness tlie ooiiditioiis uiidci winch they wcic made The best d.iys upon \^hich to undtit.ike ladiation obseivations are tliose winch aic pcifectly cloudless, and, if possible, only such should be selected But duimg the whole staj on Caioline Island there was no cloudless day, and conscquentlj none of tlie observations weic made undei the best circuinstaiices Ho\\evei, on hcveral d.ijs, there were inteivals of se\eial bonis when the sky wascleai, and lesults of some value can be obtained at such times Tlie clouds, moreover, which so continuously prevailed were'ot the cuniulns tjpe, and these have, at least approximately, the effect of a scieeii placed bcfoie the sun, concealing it foi the tune being, but allowing it to shine again with its foimcr power when they have passed The metcoiological iccord shows that clouds of other vaiiotios weie iiuelj observed, though a haze was noted at tunes Tlie conjugate thermometers weie very sensitive to a slight diminution in the sun's heat I t lequiied only a very thin cloud to reduce the leadings by many degices, and it was some minutes aftei the passage of a cloud before the instininents rose to their pioper teuipeiatuie again Prom fifteen minutes to lialf an hour sliould be allo\\cd after tlic tciiipoiary coiiceahneiit ot the sun bcfoio the leidiiigs may be considered reliable, and a longer time may bo uecessaiy lu the case of the VIOLLE bulbs, winch aic slowei in their action on account of the time required foi the bnlbs of the tlieimoineteis within the spheres to be aflected by changes in the terapeiatnie of then outci suilaces It we select fiom the obseivations those in which the sun wa§ cleai at the tune, and Iiad been foi at least fifteen minutes pic\iously, we shall hnd a sufhcient uumbei to wariant a more extended examination I t is possible to obtain from them an estimate of the bolai intensity by sc\oial metiiods, and to institute a compaiison between them I t is also possible to obtain a value of tlie solar constant I n the computation which follows the solai intensity is obtained bj tlie methods available foi the conjugate theimometers, VIOLLE'S bulbs, and black and bnght bulb tliciinom eteis, and a compaiison made of the results, and in addition a value ot the solai constant is determined from the obseivations with the conjugate thermometers 

68 MEMOIRS OF T H E NATIONAL AOADEMT OF SCIENCES 1 hrnvcTiON or OBsnrvATioKS NADF WITH inr coirjuoArr TnritiiourTrBS T h e bnllotins o f the G c n t i n l Physical O b s e i v n t o i y o f Montsoniis contain a gcneial description of t h e instrninents, b n t no r i g i d i n v e s t i g a t i o n of t h e n t h e o i y T h e differences between t h e i c a d i n g s o f t h e b l a c k a n d b r i g h t t l i e i n i o m e t c i s a i e t a k e n as a m e a s n r e o f t h e snn's i n t e n s i t y , a n d . i i e nscd III t h e f o i i n n l a P—t = Op; m v h i c h T ' , t a i c t h e l e a d i n g b o t t h e t h e i m o m c t c i s r e s p e c t i v e l y , d t h e s o l a r c o n s t a n t , j> t h e d i a t h e i m a n c y const.inti, a n d c t h e t h i c k n e s s o f t h e l a i i e i s o f a t m o s p h e i i c air tia^erscd by the solai rays I t i s r e c o g i i i / e d , h o w o v e i , t h a t t h e v a l u e s o f i9 o b t a i n e d b y t i n s f o r m u l a a r e n o t t h e t i u o s o h i r c o n s t a n t , b n t \aiy w i t h t h e i n s t i n m e n t s used,* h a M n g a v a l a o o f 17° i n t l i c i n s t r n m e n t s used a t M o n t s o u i i s F o i the pniposos o f compaiison ot t h e observations m a d e f r o m t i m e t o t i m e , i t i s s u g g e s t e d t h a t a c o n v e n t i o n a l v a l u e o f 1 0 0 ° b e a d o p t e d l o r 0, a n d t h a t obseivations w i t h d i f f e i c n t i n s t r u m e n t s be reduced to this standaid by multiply ing b y a l a c t o i d e p e n d i n g ui>on t l i e v a l u e o f 6 fox each i i i s t i u m e i i t A t Slontsouiis, where 6 = 1 7 ° f o i the p a i r of i i i s t i u m e n t s d e s c r i b e d , t h e f a c t o i is J ^ " = 5 SS, a n d t h e p i o d n c t o f t h e obsei ^ c d d i f l c r e n c e s 2* — « b y t i n s f a c t o i i s csilled t h e " a c t i m o m e t i i c d o g i e e " I n t h e case o f o b s e M a t i o n s m a d e i n 1873 a n d 1874 t h e d i f f e i e n c e s 2 ' — t a r c p u b l i s h e d , b u t i n o b s e i v a t i o n s since t h a t t i m e t h e a c t i i n o m c t i i c d e g i c o is c o m p u t e d Q u i t e r e c e n t l y a i i g i d i n v c s t i g . i t i o n o t t h e t h e o i y o f these i n s t i n m e n t s has b e e n m a d e b y T r o f W I L L I A M F F B B E L , a n d is t o b e p u b l i s h e d i n T r o f e s b i o n a l P a p e i o f t h e U n i t e d ' S t a t e s S i g nal Sex v i c e N o XIII I t assumes t h e l a w of D U L O N O ind PETIT, a n d d c i i v e s f o i m n l a i fox d e d u r i n g t h e s o l a i i n t e n s i t i e s a n d also t h e s o l a i c o n s t a n t Tiixough the couitcsy ot t h e a n t h o i , t h e f o i m u l i b h a v e been f n i n i s h e d fox t h i s c o m p u t a t i o n i n a d v a n c e o f t h e n p n b l i e a t i o n Tlioy aie as follows " Let 0 = the temperature ot the black bnlb 0i = t h e t o m p e r a t u x e o f t h e b r i g h t b u l b 0' = t h e t e m p o r a t n i e o f t h e i n e l o s n i e (shade t e m p a p i n o x ) I = t h e i n t e i i s i t j o f solax x a d i a t i o n ( c a l o i i o s p e i m i n u t e o n s q u a i e c e n t i u i e t i e ) II = c o n s t a n t 1 0 0 7 7 ( l o g n = -j^^) e = c o n s t a n t t o bo d c t e i m i n e d f i o m o b s e x v a t i o n We have then t h e f o l l o w i n g xclations (1) I = i3Si(fiO-.fje-) = 4 584;*»'(;*»-e'—1) (2) 1 = 4 5 8 4 (fA8—jie,)e= 4584(/<•-,—l)c (3) Mf = Cf^' + {l-e)fj<>'' F r o m (1) t h e i n t e n s i t y is o b t a i n e d f x o i n t h e x c u l i n g s o f t h e b l a c k b n l b i n v a c u o a n d t h e aix t « m p e i a t u x e , w h i c h i s a p p i o x i m a t o l y e q n a l t o t h a t o t t h e inolosuxe ox f i o n i (2) t h e i n t e n s i t s i s obtained from t h e readings o f the black and blight bulbs in vacuo, the ( o n s t a n t c being o b t i i n o d f r o m (3) T h e m e t h o d assumes t h a t c c m be o b t a i n e d f i o i n obseivAtion, a n d t h u s t h e i c u l i i i g s of t h e b l a c k a n d b i i g h t b u l b s i n v a c u o b e used i n c o m p u t i n g t h e ^olax i n t e n s i t i e s , 0, 0|, a n d O' are expressed i n c o n t i g i a d o dcgxees "Bnll Mens cIcl'Olis Pli>s Cpnti ilo MoiitBoniis, 1U74, p IPO 

S O L A E E C L I P S E , M A Y C, 1883 69 I t first becomes ncces-sary to compute the constant c. From (3) we liavc— In 01 del to obtain the value ol c under varying conditions, observations were selected irom different days and atdifleient times of the day. The following table contains the obseivations used and the resulting va,lues CompvtaUon ofc. No of 0 0' c D.atc Time obs Oi o o o C A p i i l 27 9 00 ,a III , 12 1") p m 2 58 9 43 4 29 7 1 79 28 0 3") a III to 2 03 p 111 10 bl 4 45 7 30 J 1 87 30 1 00 p in to 5 00 p 11. 5 52 9 .W 6 28 b 1 74 ^0 7 00 .1 III , 5 00 p in 2 44 8 M 6 28 2 1 50 iO '» 00 a III , 1 00 p III 2 58 O 42 9 2') 7 1 74 M.ty 1 6 55 a in to 10 30 . i III 10 5t 3 .50 7 20 J 1 72 2 10 )0 I ni to 2 30 p III 10 63 8 46 7 W7 1 82 2 11 iOa m to 12 V) p III 3 64 8 46 0 W9 1 78 2 7 00 .1 ni , > 00 p in 2 45 3 35 1 28 0 1 65 2 10 00 a na, 2 00 p ni 2 62 5 46 1 30 3 1 85 2 8 00 a III , 4 00 p 111 2 55 2 40 2 28 9 1 68 The resulting values ot c aie quite discordant, .ind have a inaiked progression according to the values of o, or according to the iiour ot observation. They sliow that in tiie obseivations undci discussion c is not strictly a constant, but varies with the tune of day. This may bo true ot the particulai instinments used, or be due to some circumstance connected with the exposnic ot the instiuinciits in these obseivations, or it may be inherent m this method of meas niing solar ladiation. Without tuithci cxpernncnt it is impo.ssiblc to discovci the cansc. I t is tiieiefore necessary to inquire what error i> iiitiodnccd b,v assuming a constant value of c. F o r Ins investigation the \aluc c = 1 75 was assumed, and a computation of 0' made for olwervations on Ms\}) 1 and 2. Tiic following table gives the lesult of the computation and a comp.xrison with the observed values of the same quantity Compaitson of computed loith observed sliade temperatures {ff'). MAY 1 Tunc 0 0 0' obs 0' comp Obs — comp AM o o o o o 7 00 43 7 3H 4 28 2 25 0 -f 32 7W 50 2 37 1 28 6 26 7 + 10 8 iO 54 1 40 5 20 7 20 1 + 0 6 0 00 57 2 42 2 20 8 20 7 + « 1 0 !0 50 I 41 1 20 8 10 0 — 02 10 00 60 6 44 6 30 0 11 1 — 11 10 iO 62 1 45 4 30 1 31 3 — 10 11 00 61 C 46 3 29 9 31 0 — 17 12 00 64 8 46 6 30 3 31 0 — 07 P M 1 00 03 5 46 0 .10 4 32 2 — 18 2 00 12 6 45 4 10 0 10 8 — 0 8 3 00 58 8 43 3 29 5 30 3 — 0 8 ,i 40 55 1 40 8 20 3 28 0 + 04 

70 MEMOIRS O F T H E NATIONAL A C A D E M Y O F SCIENCES MAY 2 A M 7 00 43 J 31 1 27 8 2r 2 + 1f 7 40 40 9 37 0 28 > 26 4 + 'i I « 00 4 1 10 3 28 0 27 0 + I 3 8 50 2 4 5) 5 »0 1 28 ) + 06 J 00 8 0 42 5 2) 5 20 1 + 02 10 00 62 2 4 50 0 51 4 — 14 10 50 (3 2 4( 2 50 7 31 8 — 1 1 11 00 ( t 2 40 / 50 ( 31 8 — 12 11 50 6 1 47 0 31 0 31 , — 0> 12 00 f4 7 41 8 51 0 51 ) — 0 r M 12 50 01 8 46 9 30 8 51 0 — 0 3 1 00 (4 0 47 2 50 6 52 4 — 18 2 00 (2 8 4r 3 30 0 55 5 — 27 2 0 60 8 4 8 30 4 53 5 — 2 9 5 00 02 1 44 2 2) 2 28 ) + 03 5 30 8 12 4 20 2 28 8 + 04 4 00 6 2 41 0 28 0 28 5 + 0( 4 30 2 1 58 7 28 4 27 f + 08 00 46 7 IG 0 28 2 27 1 + 09 Tbis tiblc sbows tbc effect of using a constant A ahic of c between tlic lioiiis ot 7 00 i in and 5 00 p m Ilad the \ahie c = 1 78 been eml)lo^etl, tbc computed vabics would have been diininisbcd by about O 0 5 , and tbe mean of tbe lesidnals would lia\o been nearly 0 Thcic still would lia^e remained, is w is e \ p c a c d , plus icsidual" foi the moining and e^cn^lg obsoirations. Hid minus lesiduils ioi thoso tiken nexi the middle ot the d i j Tbe nngnitndc ot the residuals, whih laiger thin was hoped foi, is not sufhcicnt to pre\eiit the use of the method, but it lendeis idMSible the (omputition of the solai intensities bj equation (1) as well as equation (2) I n tbe lattei equation it was decided to use the value c = 1 8 The following tible contiiiit> the obseixations selected for tbe computation and the solar intensities obtained bj equations (1) and (2) Those ob&ci\atioiis oiil) WAIC used in which the suu had been c l e u foi some time before the obscr\ation l l i c mean of the coiiespondiiig leadings with the two pans of mstiuinents was tal en and the resulting \aliies con\eited into cci tigndc decrees Comimtation of solar intenstttes [Conjugate thoimomotcis ] APRIT 28 Iiitcnsitj ( I ) I inie 0 0 0 0-0 0 —0 a—6 Mean a from (2) b fiom(l) \ M 9 00 ) 0 42 2 21 0 lb 8 30 0 1 -0 1 435 + 0 09 1 3 J 50 8 8 42 6 2f) 5 if i 2) , 1 \) 1 4)8 + 0 06 1 4J J 1 94 43 1 2J 5 If 5 50 1 1 50 1 4J1 + 0 04 1 1 10 00 )9 2 45 1 29 t 16 1 2) 3 1 12 1 47f + 0 04 1 40 10 5 ) J 43 0 2) ) 16 0 30 0 1 o09 1 1)5 + 0 02 1 0 11 00 01 3 4) 4 30 1 1) J 51 2 1 jl7 1 jf2 — 0 04 1 4 11 50 60 9 4o f 50 4 1J 5 50 1 1}9 1 27 — 0 07 1 4) 12 00 (2 6 40 1 50 7 11 31 9 1 87 1 (01 — 0 02 1 60 1 A! 12 50 01 47 9 31 0 16 G 33 1 010 1 70) — 0 09 1 66 1 00 62 0 46 9 50 ( I 1 51 1 1 4J2 1 M — 0 13 1 J2 1 50 CO 7 40 0 50 0 14 1 30 1 1 543 1 06 — 0 10 1 45 

Fig. 19. CURVES OF BLACK AND BRIGHT BULB THERMOMETERS DURING ECLIPSE VBVKA Tihe ? M lO-OO 10.15 10 30 1045 1100 U 15 11 30 11'45 1200 1.\Zt5 1Z50 12 '45 IM tlA \~105' of -100° Black bulb freely 03q)osocl Biiglit " Sopoi-ito nb*icrvutioim of black bulb o " " bngbt ' • ? Denotes suii in Uoudfl nt tune of i eidiiig Other ro-uliugs wore soinetiinos iiroctod bj Uouds l)re\^nn8 to the obscmtioM J I I L 

SOLAJl E C L I P S E , MAY G, 1883 71 Computation of iolar t»ten6»fi««—Gontnined. APRIL 20 IiitciiBiliy ( I ) Tiiiio 0 01 0' O—Oi ft-6 Mean a fioui ( 2 ) b fioiii ( l ) A M •1 00 '* 8 41 1 2') 9 V> 7 20 9 1 447 1 m + 0 12 1 « III oil h i <J 44 7 30 0 17 2 i1 1 1 040 1 -i74 + 0 07 1 01 11 00 (•1 S 44 (• 30 8 10 0 fO 4 I Wfe 1 -iJ-i + 0 O'l 1 Vi 11 (hi 4 4'i 7 to <) 10 7 Jl ') 1 001 1 WJ + 0 01 1 O'l 11 w (iJ 'J 40 1 i\ 0 10 8 31 9 1 01b 1 012 + 0 01 1 02 11 4-| b< 1 40 } M 7 10 8 Ai 4 1 020 1 0% — 0 02 1 Oi I! 00 02 b 40 J SO 0 10 J U 0 1 •i08 1 014 - 0 05 1 •V) r M U 1J III 0 40 0 M & 10 4 12 2 1 %l 1 027 — 0 01 1 00 12 )0 (it 1 40 •) )1 1 10 2 U 0 I -lOO J 021 — 0 1)0 I V» 1 <U liU 4 40 2 10 ') 14 2 2-) 1 £>^ 1 470 — 0 12 I 41 2 10 19 4 4J '1 JO ') If 5 28 'i 1 281 1 4'21 — 0 14 1 Ti 2 W IS 9 4'i 0 H) 8 11 t 28 1 1 2'i7 1 m - 0 11 L {( { 00 •V) 1 44 0 .{0 0 14 0 28 0 1 378 1 417 — 0 14 1 40 A P R I L 30 - A M 11 00 01 9 40 7 10 4 18 2 31 0 1 771 1 7Vj + 0 02 1 70 11 JO 01 9 47 4 JO 1 17 -) J4 4 1 700 ] 7-il — 0 01 1 7J 11 4'> 04 7 47 J JO 4 17 4 34 J 1 OTi 1 74 J — 0 0-1 I 72 12 00 04 ') 47 7 30 4 17 2 J4 5 1 078 1 735 - 0 08 I 72 r M m 01 0 47 0 JO 4 17 0 34 2 1 OTib 1 7J7 - 0 08 1 70 12 15 1 00 M 4 41 0 2<) I V) 4 2'l 1 1 4I<1 1 4J0 0 00 1 44 1 •«! JO 4 41 7 20 o 14 7 27 2 1 J-i7 1 JJ2 + 0 02 1 J4 4 00 54 1 40 3 28 8 IJ ') 2-1 J 1 201 1 22-1 + 0 04 1 24 4 JO •iO 2 J7 'J 28 4 12 J 21 b •1 0')3 I 0J9 + 0 0-) 1 07 5 00 4") J5 2 28 J 10 0 10 'IS 0 83J 0 78S + 0 00 0 b2 MAY 1 A M 0 45 J<) 8 31 1 28 0 8 7 11 8 0 72 J 0 5J8 + 0 18 0 01 7 00 4J 7 JJ 4 28 2 10 J 15 5 0 870 0 719 + 0 10 0 80 7 11 4u 0 35 1 28 4 11 5 18 2 0 WO 0 855 + 0 14 0 9J 7 JO 2 17 J 28 0 12 9 21 0 1 14J 1 029 + 0 11 1 O'l b JO 54 J 40 5 29 7 IJ 8 24 0 1 2-i8 1 1% + 0 00 1 2J 8 4<j 57 J 41 9 2'> 0 15 4 27 5 1 427 1 J55 + 0 07 1 J<) <> 00 •>7 2 42 8 39 8 15 0 27 4 1 J')2 1 348 + 0 (M 1 J7 9 30 10 00 59 1 00 0 4J 44 J 0 29 30 8 0 15 10 8 0 29 JO J 0 1 1 484 517 1 1 453 528 + — 0 0 OJ 01 1 1 47 -(2 10 JO 02 1 45 4 .JO 1 10 7 Jl 8 1 vm 1 599 0 00 1 00 11 00 OJ 0 40 J 29 ') 17 'J 13 7 1 073 1 702 — 0 01 1 09 12 00 1* M 04 b 4b 0 30 i 18 2 34 5 1 770 1 753 + 0 02 1 70 03 -| 40 0 JO 4 10 9 J3 1 1 CJJ 1 07 J 0 Oi 1 05 1 00 2 00 J 00 02 53 0 8 4'i 4J 4 3 10 29 0 5 17 15 2 5 J2 29 0 3 ] 019 1 454 1 1 041 4.50 + 0 0 01 00 1 1 04 45 3 10 55 1 40 b 29 i 11 J 25 8 1 110 1 257 + 0 05 I 2a 

72 MEMOIES O F T H E NATIONAL A C A D E M Y OP SCIENCES. Computation of solar intensities—Gontmued. MAY 2. Intens t y ( i ) Time e 0 — 0i. e— o- b Mean a from (2) b from(l) A. M 7 00 43 9 34 1 27 6 9 8 16 1 0 838 0 747 + 0 09 0 79 7 40 49 9 37 0 28 5 12 9 21 4 1 141 1 018 + 0 12 1 08 8 00 54 1 39 3 28 9 14 8 25 2 1 341 1 221 + 0 12 1 28 8 30 52 4 39 3 29 1 13 1 23 3 1 181 1 123 + 0 06 1 15 a 10 00 00 58 0 62 '2 42 3 45 5 29 3 iO 0 15 16 7 7 28 32 7 2 1 461 1 601 1 415 1 617 + 0 0 05 02 1 1 44 01 10 30 63 2 46.2 30 7 17 0 32 5 1 641 1 643 0 00 1 04 10 11 45 00 63 6 64 2 46 2 4'i 7 30 6 30 6 17 17 4 5 33 33 0 6 1 681 1 697 1 671 1 706 + 0 0 01 01 1 1 68 70 11 15 64 9 47 1 31 1 17 8 33 8 1 7:« 1 724 + 0 01 1 73 11 30 65 1 47 0 31 0 18 1 34 1 1.763 1 740 + 0 02 1 75 12 p M 00 04 7 46 8 31 0 17 9 33 7 1 741 1 716 + 0 02 1 73 12 30 64 8 46 9 30 8 17 9 '34 0 1 743 1 731 + 0 01 1.74 1 00 , 64 6 47 2 30. 6 17 4 34 0 1 694 1 728 0 03 1.71 2 00 62 8 46 8 30 6 16 0 32 2 1 542 1 625 — 0 08 1 58 o 30 60 8 45 8 30 4 15 0 30 4 - 1 431 1 5^1 — 0 09 1 48 3 00 62 1 44 2 29 2 17 9 32 9 1 707 1 648 + 0 06 1 68 3 30 58 5 42.4 29 2 10 1 29 3 1 504 1 447 + 0 Ob 1 48 4 00 56 2 41.0 28 9 15 2 27 3 1.400 1 334 + 0 07 1 37 4 30 52 1 38 7 28 4 13 4 23 7 1 204 1 137 + 0 or 1.17 - 4 45 49 1 37.2 28 3 11 9 ,20 8 1 051 0 985 + 0 07 1.02 5 00 46 7 36 0 28 2 Id. 7 18. 5 0 932 0 869 + 0 06 0 90 MAY 3 A M 10 30 61 6 44 8 30.4 16 8 31 2 1 601 1 566 + 0 04 1 58 11 00 64 3 40 4 30 8 17 9 33 5 1 736 1 703 + 0 03 1 72 11 iO 04 1 46 1 30 1 18.0 . 54 0 1 741 1 721 + 0 02 1 73 12 00 64 3 46 4 30 5 17 9 33 8 1 736 1 710 + 0 02 1.73 P M 12 30 04.1 46 6 30 0 17 5 34 1 1 695 1 727 — 0 03 ' 1 71. 1 00 63 9 46 8 30 4 17 1 33 5 1 658 1 697 — 0 04 1 08 1 30 04 1 46 9 30 4 17 2 33 7 1 608 1 708 — 0 04 1 69 2 00 62 7 45 9 30 3 10 8 32 4 1 615 1 633 — 0 02 1 62 2 30 60 5 44 3 30 0 16 2 30 5 1 535 1.523 + 0 01 1 53 MAY 5 A M 10 00 58 0 43 0 24 6 15 6 34 0 1 460 1 650 — 0.19 1.56 10 30 61.4 44 7 25 6 10 7 35 8 1 591 1 764 — 0.17 1.68 11.00 01 2 44 3 26 7 16.9 34 5 1.605 1 706 — 0 10 1.66 11 30 61.2 44.6 27 2 16 6 34 0 1.578 1 683 — 0.10 1 63 MAY 6. p . M. 1 15 59 4 43.5 29 4 15 9 30 0 1 495 1 487 + 0 01 1 49 1 30 59 4 4) 8 29 4 15 6 30 0 1 469 1 487 — 0 02 1 48 2 00 57 6 43.4 29 4 14 2 28 2 1.325 1 388 — 0 00 1.30 3 00 58 2 41 8 29.0 16 4 29 2 1 526 , 1.438 + 0 09, 1 48 3 15 56 9 40 9 29 0 16 0 27 9 1 474 1.367 + 0.11 1 42 I n the preceding table the sixth column contains the dilference between the readings of the black bulb in vacuo {d) and the bright bulb in vacuo (di), and the seventh column the differences between the former and the shade temperatures (^')' '^^^ latter, which are given in the fifth column, have been obtained from the current meteorological record; they are the reading of the 

S O L A R E C L I P S E , M A Y G, 1883. 73 mercurial thermometer in the instrument shelter, reduced to centigrade measures. I n a few cases the values were obtained by interpolation. The column of differences (a — b) shows the discrepancies between the two methods. The signs are + for morning and evening values, and — for those in the middle of the day, as should be the case by taking a constant value of c. A comparison of the two methods shows no reason for preferring one to the other. The one which introduces the value of c—equation (2)—is open to the objection that it assumes a constant value for c which it has been shown is only approximately true; it is possible that the deviations from constancy are due to the circumstances of these particular observations, and that consequently the intensities are not strictly accurate as computed. On the other hand, the method which uses the shade temperatures—equation (I)—is open to the uncertain- ties in the observations of that quantity, and assumes that these temperatures may be adopted as the temperatures of the inclosure of the black bulb thermometer. There seemed to be no reason for giving preference to either of the reductions. The last column contains the mean of the two series of values, which are adopted as the solar intensities given by the conjugate thermometers. 2 REDUOTION OF OBSERVATIONS MADE WITH VIOLLE'S BULBS The theory of these instruments is given by the inventor m his work upon solar radiation, above referred to, pj). 17-22 *. According to the method there explained, the intensities may be obtained by the equation: uu' in which u = the difference between the reading of the thermometer in the blackened sphere and the air temperature. u' = the'difference between the reading of the thermometec in the gilded sphere and the air temperature. a = the absorbing power of the gilded sphere in terms of that of the blackened sphere. K =a. constant depending ujion the instrument, and found by the methods explained. I f K I S undetermined, relative intensities can be obtained by the equation- uu' 1 = u'— a It In this equation the quantities u and u' are obtained directly from the observations, but the constant a must be derned experimentally. After the return of the expedition, a number of observations of this constant were made by screening the spheres and observing the rate of cooling of each, and also by observing the rate of increase of temperature when full sunlight was allowed to fall upon them after Ihey had assumed the shade temperature behind the screen. The experiments gave the value a = 0.5, the large value being due to the tarnishing of the gilt, which was caused in part by the effect of the sea voyage. It is in part also apparently due to the poor manner in which the gilding has been done, as the same deterioration has been found in instruments which have never been used in actual work. Similar observations with a pair of instruments in which there was a good polish on the gilded sphere gave the valne a = 0.3. I t was decided to use the value 0 4 in the reduction as probably representing nearly the correct value for the condition of the gilt at Caroline Island. A n approximate value is sufficient for determining the relative intensities, which is the aim of the present investigation. The following table contains the computation for the same dates and tunes at which the readings of the conjugate thermometers were reduced. Other observations were reduced, but it I S thought unnecessary to give the computation, as they show discordances due to the eftect of passing clouds to a greater degree than those here given. * See also Anttales de Chiime et tie Physique, 5= sdne, t. X V I I , 1879 S. Mis. 110 10 

74 M E M O I E S O F T H E N A T I O N A L A C A D E M Y OP S C I E N C E S . Computation of relative solar inte^mttes. [ V I O L L E ' S bulbs ] A P R I L 28 Time Black. Gilt Air. u u' I A. M 9 00 40 8 36 4 29 4 11 4 7 0 33 2 9 30 41 1 36 6 29 3 11 8 7 3 33 1 9 35 41 8 37 2 29 3 12 5 7 9 34 1 10 00 41 0 36 3 29 4 11 6 6 9 34 8 10 35 43 0 38 2 29 9 U 1 8 3 35 1 11 00 43 8 .38 7 30 1 13 7 8 6 38 0 11 30 43 4 38 6 30 4 13 0 8 2 35 5 12 00 44 4 39 2 30 7 13 7 8 5 38 8 P M 12 30 46 3 40 4 31 0 15 3 9 4 43 6 1 00 45 2 39 7 30 6 14 6 9 1 40 3 1 30 45 1 39 6 30 6 14.5 9 0 40 8 A P R I L 29 A M 9 00 39 7 .16 0 29 9 9 8 6 1 27 2 10 00 43 1 38 9 30 6 12 5 8 3 31 4 11 00 45 6 3H 2 30 8 14 8 7 4 73 0 11 15 45 6 38 7 30 9 14 7 7 8 60 3 U 30 45 6 39 9 31 0 14 6 8 9 41 9 11 45 45 6 39 5 30 7 14 9 8 8 46 8 12 00 45 5 39 9 30 6 14 9 9 3 42 0 P M 12 15 45 5 39 8 .<0 8 14 7 9 0 42 7 12 30 45 5 40 2 U 1 14 4 9 1 39 7 1 30 46 0 39 5 30 9 "15 1 8 6 49 9 2 10 46 0 39 7 .iO 9 15 1 8 8 47 5 2 30 46 0 39 7 iO 8 15 2 8 9 48 3 3 00 46.0 39 2 30 6 15 4 8 6 55 2 A P R I L 30. A M 11 00 46 7 42 6 30 4 16 3 12 2 34 9 11 30 46 2 ' 41 8 30 5 15 7 11 3 35 5 11 45 45 4 40 8 30 4 15 0 10 4 35 5 12 00 46 5 41 9 30 4 16 1 11 5 36 3 P M 12 15 45 5 40 5 30 4 15 1 10 1 37 2 3 00 41 7 W 4 29 3 12 4 8 1 32 4 3 30 39 8 35 5 29.2 10 6 6 3 31 8 4 00 39 5 35 9 28 8 10 7 7 1 27 1 4 30 36 7 }4 2 28 4 8 3 5 8 19 3 5 00 35 2 ;52 4 28 3 6 9 4 1 21.8 1 MAY 1 A M 7 00 « 5 .n 3 • 28 2 5 3 3.1 16 4 7 15 34 4 32 0 28 4 6 0 3 6 18 0 7 30 37 5 •M 1 28 6 8 9 5 5 25 8 8 30 40 8 36 5 29 7 11.1 6 8 31 4 8 45 41 8 37 5 29 8 12 0 7 7 31 9 9 00 42 b 38 4 29 8 12 8 8 6 31 4 9 30 44 0 39 6 29 8 14 2 9 8 33 9 -10 00 44 6 40 0 30 0 14 6 10 0 34.8 10 30 44 a 39 9 30 3 14 5 9 6 36 6 11 00 46 9 41 8 29 9 17 0 11 9 39 7 12 00 47 2 41 6 30 3 16 9 11 3 42.4 P M 1 00 46 7 41 3 30 4 16 3 10 9 40 4 2 00 46 2 40. 7 30.0 16 2 10 7 41 3 3 00 4b. i 40. 3 29 5 15 9 10.8 39 0 3.40 43 0 38 7 29 3 13 7 9 4 33 0 

S O L A E E C L I P S E , M A T 6, 1883. 75 Computation of relative solar intensities—Continued. MAY 2 Time. Black Gilt An. n «' I A M 7 00 32 9 30 rt 27 8 5 1 J0 15.3 7 40 38 0 34 9 28 5 9 5 6 4 ' ^ 23 4 8 00 40 3 36 5 28 9 11 4 7 6 28 9 8.30 39 8 36 5 29 1 10 7 74 25.5 9 00 42 0 38 0 29 3 12 7 8.7 30.7 10 00 45 6 40.5 30.0 15 6 10.5 38 1 10 30 45 5 40 8 30 7 14 8 10 1 35 6 10 45 45.9 41 0 30 6 15 3 10 4 37 0 11 00 46 3 41 3 30 6 15.7 10 7 38.2 11 15 47.0 41 7 31 1 15.9 10.6 40 1 11 30 46 9 41 7 31 0 15 9 10 7 39 6 12 00 46 2 41.1 31 0 15 2 10 1 38 4 P M 12 30 46 0 41 6 30 8 15 2 10 8 34 9 1 00 47 9 42 6 30 6 17 3 12 0 40 7 ' 2 00 49 1 43 6 30 6 18 5 13 0 42 9 3 30 47 8 42 7 30 4 17 4 12 3 40 4 3 00 47 5 42 4 29 2 18 3 13 2 40 9 3 30 44 8 40 4 29.2 15 6 11.2 34 9 4 00 43 9 39 6 28 9 15.0 10 7 34 1 4 30 40.0 tb 8 28.4 11 6 84 25 6 4 45 37 0 34 1 28 3 8 7 5.8 21 9 5 00 35 9 33 3 28 2 77 5 1 19 6 MAY 3 A M 10 30 43.6 3d 7 30 4 13 2 8 3 36 5 11 00 44 2 39 2 30 8 13.4 8 4 37 5 11 30 44 5 39 5 30 1 14 4 9 4 37 6 12.00 44 9 39 8 30 5 14 4 9 3 38 3 P M 12 30 45 2 40 0 30 0 15 2 10 0 39 0 1 00 45 9 40 5 30 4 15 5 10 1 40 1 1 30 46.2 41 0 30 4 15 8 10 6 38 9 2 00 44 8 39 8 30 3 14 5 9 5 37 2 2 30 43 9 39 1 30 0 13 9 9 1 36 1 MAY 5 A M 10 00 39 7 35 7 24 6 15 1 11 1 32 9 10 30 41 7 37 2 25 6 lb 1 11 b 35 9 11 00 40 8 36 3 26 7 14 1 9 b 33 8 11 30 41 4 36 7 27 2 14 2 9 5 35 5 MAY 6 P M • 1 15 39 7 36 0 29 4 10 3 6 6 27 2 1 30 39 8 36 1 29 4 10 4 6 7 27 9 2 00 30 7 3b 0 29 4 10 3 6 b 27 2 3 00 39 5 35 8 29 0 10 5 6 8 27 5 3 15 38 6 35 3 29 0 9 6 6 3 24 2 I t lb evident from an examination of the values in the last column that observations were often made when the instruments had not recovered from the effect of passing clouds. This is especially true on April 29, which is here given as an illustration of the effect ot frequent clouds upon the indications of the instruments. This sluggishness seems to be greater than that of the conjugate thermometers. Further remarks on this point are given below m the section devoted to a comparison of the results of the different computations. 

76 MEMOIRS O F T H E NATIONAL A C A D E M Y O F SCIENCES. 3 REDUCTION OF OBSERVATIONS MADE WITH THE BLACK AND BRIGHT THERMOMETERS EXPOSED IN FULL SUNLiaUT, BUT NOT IN VACUO The same formula used for the reduction of observations with V I O L L E ' S bulbs serves for the computation of solar intensities fiom readings of black and bright bulb thermometers not in vacuo. The absoiption constant a is, however, different. I n the computation, the results of which are given in the following table, the value « = ^ is adopted as representing the theoretical value of the radiating power of the bright bulb in terms of that of the black bulb • Computation of relative solar intensities. [Black and bright bulbs not m vacuo ] A P R I L 28 Time 1137 1136 Air u' I A SI 9 00 36 3 32 9 29 4 6 9 A5 10 5 9 30 38 1 33 3 29 3 8 8 4 0 14 1 9 35 37 8 33 3 29 3 8 5 4 0 13 1 10 00 38 2 33 0 29 4 8 8 A 6 15 1 10 35 39 1 34 6 29 9 9 2 4 7 13 5 11 00 39 2 34 6 30 1 9 1 4 5 13 6 11 30 38 3 34.4 30 4 7 9 4 0 11 7 12 00 40 6 35 7 30 7 9 9 5 0 14 6 P M 12 30 41 4 36 4 31 0 10 4 5 4 15 2 1 00 40 0 36 0 30 6 9 4 5-4 13 4 1 30 39 6 35 6 30 6 9 0 5.0 12 9 A P R I L 30 A M 11 00 42 8 37 2 30 4 12 4 6 8 17 9 11 W 40 8 36 7 30 5 10 3 6 2 14 2 11 45 42 9 37 5 30 4 12 5 7 1 17 8 12 00. 43 3 38 1 30 4 12 9 7 7 18 1 r M 12 15 43 0 37 7 30 4 12 6 7 3 17 7 3 00 36 9 33.9 29 3 7 6 4 6 10 6 3 30 36 8 33 1 29 2 7 6 3 9 11 4 4 00 36 4 32 5 28 8 7 6 3 7 11 7 4 30 34 2 30 8 28 4 5 8 2 4 9 9 MAY 1 A M 7 00 31 8 29 2 28 2 3 6 1 0 9 0 7 15 32 5 29 6 28 4 4.1 1 2 9 8 7 30 33.4 30 6 28 6 4 8 2 0 8 0 8 30 36 7 33 3 29 7 7 0 3 6 10 5 8 45 36 8 32 9 29 8 7 0 3 1 11 4 9 00 37 5 33 6 29 8 7 7 3 8 11 7 9 30 38 4 34.4 29 8 8 6 4 0 12 4 10 00 39 4 35 0 30 0 9 4 5 0 13 8 10 30 39 7 35 6 30 3 9 4 5 3 13 5 11 00 4L4 37 3 29 9 11 5 7 4 15 5 12 00 41 4 37 4 30 3 11 1 7 1 14 9 P M 1 00 41 9 37.3 30 4 U 5 6 9 15 9 2 00 41 2 36 1 30 0 11 2 6 1 16 3 3 00 39 2 35 0 29 5 9 7 5 5 13 7 3 40 37.5 33.6 29 3 8 2 4 3 12 2 

S O L A E E C L I P S E , M A Y 6, 1883. 77 Computation of relative solar intemities—Coutimied. MAY 2 Time 1137 • 113b Air u It' I A M 7 00 30 7 28 9 27 8 29 1 1 5 3 7 40 32 9 30 b 28 5 44 2 1 6 6 8 00 34 7 31 7 28 9 5 8 2 8 9 0 8 30 36 8 ii 8 29 1 7 7 3 7 11 9 9 00 38 3 33 6 29 3 9 0 4 { 13 8 10 00 40 4 35 b 30 0 10 4 5 6 14 9 10 30 39 4 35 4 30 7 87 4 7 12 4 10 45 40 8 35 8 .JO b 10 2 5 2 15 2 11 00 41 1 36 1 30 6 10 5 5 5 15 6 11 15 42 1 36 9 31 1 11 0 5 8 16 0 11 30 42 9 36 9 31 0 11 9 5 9 18 0 12 00 41 1 36 5 31 0 10 1 5 5 14 6 P M 12 .JO 41 8 3b 9 30 8 11 0 6 1 15 b 1 00 42 8 36 9 AO 6 12 2 6 3 17 9 2 00 41 8 .J7 1 W 6 11 2 6 5 15 8 2 30 40 3 36 4 30 4 9 9 6 0 13 5 3 00 40 1 35 3 29 2 10 9 6 1 15 5 3 30 39 3 34 4 29.2 10 1 5 2 15 0 4 00 « 3 33 b 28 9 9 4 4 7 14 2 4 30 36 3 31 4 28,4 7 9 3 0 14 0 4 45 33 9 30 6 28 3 5 6 2 3 9 2 5 00 33 1 30 3 28 2 4 9 2 1 7 9 MAY 3 A M 10 30 40 0 35.6 30 4 9 6 5 2 13 9 11 00 40 0 35 7 30 8 9 2 4 9 13 3 11 30 40 8 3b 1 30 1 10 7 6 0 15 3 12 00 40 8 36 4 30 5 10 3 5 9 14 5 P M 12 30 41 1 3b 7 30 0 11 1 6 7 15 6 1 00 41 8 3b 7 30 4 11 4 6.3 16 ^ 1W 41 4 37 1 30 4 11 0 b7 15 0 2 00 41 1 36 2 30 3 10 8 5 9 15 6 2 30 39 4 35 6 30.0 9 4 5 6 13 2 MAY b p. M 1 15 36 7 33 1 29 4 7 3 3 7 10 8 1 30 37 1 33 2 29 4 7.7 3 8 11.7 2 00 36 8 J3 1 29 4 74 3 7 11 0 3 00 36 2 32 9 29.0 7 2 3 9 10 4 3 15 35 4 32.2 29 0 64 3 2 9 8 A n examinatiou of the values of the intensity given in the last column shows many irregu- laiities. This is not due to the eftect of passing clouds, as m the former methods, for the thermom- eters reco\ er quickly their former condition after the clouds have passed, but to changes m the velocity of the wind. The method is confessedly approximate, since the least increase m the force of the w ind which blows on the bulbs, or the least decrease, changes the effect of convection and so produces discordancies in the observations. The values obtained are theretore more of interest for comparison than for their intrinsic merit. 4 COMPAEI&ON OF THE MELATim INlENIiITIES I t remains to make a comparison between the intensities obtained by the three methods in use. For this purpose they must be reduced to a common scale. The intensity at 12.00 on May 1 

78 MEMOmS O F T H E NATIONAL ACADEMY O F SCIENCES. has been taken as 1, and the intensities at other tunes divided by the intensities given by each method at the chosen time. I n the first two methods the relative values are less than 1, because the intensities at 12.00 on May 1 are the highest observed (with one or two exceptions); but in the last method there are values greater than 1, because this is not the case. The relatively small value at 12.00 on May 1 seems to be due to accidental conditions. The following table contains the relative intensities bj the three methods: Comparison of relative intensities by the three methods. A P R I L 28 Couj VIOLIA'S Ordinary Timo tlierius bulbs therms. A M 9 00 0 86 0 78 0 70 9 30 0 8-> 0 78 0 95 9 35 0 8b 0 80 0 88 10 00 0 85 l' 82 1 01 10 30 0 85 0 88 0 83 10 35 0 85 0 Si 0 91 11 00 0 87 0 90 0 91 11 30 0 85 0 84 0 79 12 00 0 91 0 92 0 98 P M li 30 0 94 1 03 1 02 - 1 00 0 86 0 95 0 90 1 30 0 81 0 96 0 87 A P R I L 30 A M. 11 00 1 00 0 82 1 20 11.30 0 98 0 84 0 95 11 45 0 98 0 84 1 19 12 00 0 98 0 8b 1 21 r M 12 15 0 97 0 83 1 19 3 00 0 82 0 7b 0 71 3 So 0 76 0 75 0 77 4 00 0 70 0 64 0 79 4 30 0 bl 0 46 0 66 5 00 0 47 0 51 MAY 1 A M 7 00 0 45 0 39 0 60 7 15 0 53 0 42 0 66 7 30 0 62 0 bl 0 54 8 30 0 70 0 74 0 70 • 8 45 0 79 0 7.-> 0 77 9 00 0 78 0 74 0 79 9 30 0 84 0 80 0 8< 10 00 0 8b 0 82 0 93 10 30 0 91 0 86 0 91 U 00 0 96 0 94 1 04 12 00 1 00 1 00 1 00 P M 1 00 0 94 0 95 1 or 2 00 0 93 0 97 1 09 3 00 0 82 0 92 0 92 3 40 0 73 0 78 0 82 

S O L A E E C L I P S E , M A Y G, 1883. 79 Gompartson of relative intensities by the three methods—Continued. MAY 2. Coiij VIOLM'S Ordinary Time therms bulbs therms A M 7 00 0 45 0 36 0 36 7 40 0 61 0 .55 0 44 8 00 0 73 0 68 0 60 8 30 0 05 0 60 0 80 9 00 0 82 0 72 0 93 10 00 0 91 0 90 1 00 10 30 0 93 0 84 0 83 10 45 0 95 0 87 1 02 11 00 0 97 0 90 1 05 11 15 0 98 0 95 1 07 11 30 0 99 0 93 1 21 12 00 0 98 0 91 0 98 P M 12 30 0 99 0 82 1 05 1 00 0 97 0 96 1 20 2 00 0 90 1 01 1 06 2 30 0 84 0 95 0 91 3 00 0 95 0 96 1 04 3 50 0 84 0 82 1 01 4 00 0 78 0 80 0 95 4 iO 0 06 0 60 0 94 4 45 0 58 0 52 0 62 5 00 0 51 0 46 0 53 MAY 3. A M 10 30 0 90 0 86 0 93 11 00 0.98 0 88 0 69 11 30 0 98 0 89 1 03 12 00 0 98 0 90 0 97 P M 12 30 0 97 0 92 1 05 1 00 0 95 0 95 1 09 1 30 0 90 0 92 1 01 2 00 0 92 0 88 1 04 2 30 0 87 0 85 - 0 89 MAY 0 P M 1 15 0 85 0 69 0 72 1 SO 0 84 O.bO 0 79 2 00 0 77 0 64 0 74 3 00 0 84 0 65 0 70 3 15 0 81 0.57 0 06 The above table shows plainly the effect of temporary influences in modityiug the observed intensities, and also that the different instruments are differently affected bj the same influences. In order to eliminate the accidental peculiarities and obtain a more reliable comparison of the methods the following table has been computed. I t combines the observations made at the same hour on the different days, and uses those times only at which observations on two or more days were made. 

80 MEMUIES OF T H E NATIONAL ACADEMY OF SCIENCES. Mean relative intensities observed at the same hour on tico or more days by the three methods. Conj VIOLLE'S Ordinary Hour therms bulbs therms A 31 7 00 0 45 0 38 0 48 8 30 0 68 0 67 0 75 9 00 0 82 0 75 0 81 9 30 0 84 0 79 0 89 10 00 0 87 0 «> 0 98 10 30 0 90 0 86 0 88 11 00 0 9b 0 89 1 02 11 30 0 95 0 88 1 00 12 00 0 97 0 92 1 03 P M 12 30 0 97 0 92 1 04 1 00 0 93 0 95 1.0b 1 30 0 88 0 94 0 94 2 00 0 92 0 95 1 06 2.30 0 86 0 90 0 90 3 00 0 86 0 88 0 89 3 30 0 80 0 78 0 89 4 00 0 74 0 72 0 87 4.30 0 b4 0 53 0 80 The accompanying chart represents graphically the values given in the above table. The full curve corresponds to the intensities given by the conjugate thermometers, the dotted curve to those given by V I O L L E ' S bulbs, the broken curve to those given by the ordinary black and bright thermometers. The original values by which the curves were drawn are represented by O, •, and + , respectively. 5 SXTUMAltY OF RESULTS The discussion given in the preceding pages has given us values of the solar intensities on the-days of observation by three different methods. I t has thus furnished incidentally a means of comparison of the methods, in so far as the observations themselves allow this to be done. The uncertainties arising from the state of the sky have already been mentioned; their effect is shown m the discordances which the results at difterent horns on the same day exhibit. B y including favorable times oulv, the tables sho\\ing the relative intensities by the ditterent methods represent fairly the results obtained under the best conditions during the series of observations. The following suiniuary gives the conclusions derived from an examination of the results* 1. The method of the black and biight bulb thermometers freely exposed in the n r gives only an approximate determination of the solar intensity. This was expected, and is dne to the constantly varjing conditions of exposure, caused by the effect ot the winds on convection currents. 2. V I O L L E ' S bulbs are affected by convection, but the eftect is shown less than in freely exposed thermometers, on account of the position of the thermometers within. The observations on the afternoon of May 2, when the air was almost perfectly still, show higher intensities than the corresponding times on other da>s, but the observations are not suflBcient to indicate how much the lesults are influenced by this cause. 3. The luteusities by the conjugate thermometers seem also to be affected by the varying influence of convection, but in this case (and in the preceding also) direct experiments would give more information as to this effect than any examination of these observations. 4. The intensities by V I O L L E ' S bulbs (see the curves) are smaller in the morning and greater in the afternoon than those by the conjugate thermometers. There is a marked difference 

Fig. 13. CHART OF R E L A T I V E INTENSITIES A 2tf I Ttme of OhservcUvori PM 00 900 idoO lOOO 32 00 IS 00 J'OO 200 3 00 4.00 AOO -1.00 Coi\jugate tbcrmomotcrs Viollc'8 bulbs Blnclc and bright bnlbs -OMI 

S O L A R E C L I P S E , M A Y 6,1883. 81 in the times of the maximum readings, the V I O L L E bulbs reaching the maximum one hour later than the conjugate thermometers. This shows that the former are sluggish in their action, and at any given time show the intensity not for that time butfor a time already past by many minutes. The sluggishness of the V I O L L E bulbs was also indicated by the long time which was required after tlie passage of a cloud before their return to a normal condition 5. The cuive coirespondmg to the intensities given by the conjugate thermometers represents the relative solar intensities as accurately as the observations permit for the period April 28 to May 3. I t is impossible to give any mathematical estimate of the uncertainty of the numerical values which would be obtained from this curve. I t is probable that the values are liable to an uncertainty of several hundredths, but not as great as a tenth. They may be accepted as the final values ot the relative solar intensity obtained at Caroline Island. Expressed in terms of the 12.00 value they are as follows Relative solar intensity at^Carolme Island, April 28 to May 3, 1883. Time luteusity Time Intensity Time Intensity A M A M P M 7 00 0 47 10 30 0 94 2 00 0 9'? 7 30 0 57 11 00 0 97 2 30 0 90 8 00 0 6b 11.30 0 99 3 00 0 87 8 30 0 73 12 00 1 00 3.30 0 82 9 00 0 80 p. M 4 00 0 76 9 30 0 87 12 30 1 00 4 30 0 66 10 00 0 91 1 00 ' 0 98 5 00 0 46 1.30 0 96 6 DETERMINATION OF THE SOLAR CONSTANT \ The investigation upon the theory of the conjugate thermometers made by Prof. W I L L I A M F E R R E L (Professional Papers of the U . S Signal Service, No. X I I I ) contains formulae for the derivation of the solar constant from the solar intensities given by the observations. Adopting his notation, and referring to the Professional Paper itself for an explanation ot the method of deriving the formulae, we have the following- Let A = the solar constant,* r p = the diathermancy constant, I = the solar intensity at any given hour ot the day, -^i)J>i Ii = assumed values of the above, SA, Spi SI = the corrections to the assumed values. Then— (1) A = Ai + dA (2) < p = pi + Sp (3) I = I i + Sl Let e = the thickness ot the atmosphere through which the sun's ra>s pass (e = 1 when sun is in zenith). Then— (4) I, = A,(p,' +0.025"^ p,'-'^ (5) - - - -, 51 =pi'dA + Aiepi<'-'Up * The solar constant in Profesbor F E R B E L ' S investigation is the amount of heat received on a square centimetre of surface .at the upper limits of the atmosphere, expressed in calories The calorie is the amount of heat necessary to raise the temperature of one gramme of water 1° centigrade By these definitions the constant = 2 J ; a decimal. S. Mis. 110 11 

82 MEMOIRS OP T H E N A T I O N A L A C A D E M Y OP S C I E N C E S . I f p 18 not constant during the day then Sp t d'p must be substituted for Sp in the last equation. In § 1 there have been given values of the solar intensities obtained from the readings of the conjugate thermometers. These, after the rejection of a few discordant observations, were used in the above formulse for deriving values of A and p. The first step m the computation con- sisted in the computation of the values of e for dtfterent hours of the day by means of the well- known formulas— e = sec « cos « = sin fi sin 3 + cos ¥> cos d cos h in which— , z = sun's zenith distance, d = sun's decimation, h = sun's hour angle, f = latitude of the station. A table was computed from which the values of e were obtained for each observation. Approximate values of A and p were then obtained by trial computations with equation (4), using-a few of the observations on each day. The foUowiug were adopted: A. P April 28 1.96 0 859 29 2.18 0 760 30 2 27 0 776 May 1 3 02 0 614 2 2 20 0 805 3 2.20 0.805 With these values, equation (4) was used to give comjjuted values" of I, for comparison with the observed values. The resulting residuals were used m equation (5) to give the corrections SA and Sp by the method of least squares. I t was found by the computation that the observa- tions on April 28 were discordant, and also were not of sufficient range to give successful results since they extend from 9.00 a. m. to 1 30 only. Observations taken at early or late hours are necessary to give suflBciently large values of e for the computation. I t was also found that the assumed values of A and p on April 30, May 1, 2, 3 were not near enongh to reduce the residuals satisfactorily. Consequently a second approximation was made for these dates, using the values of A and p derived from the first computation for the dates April 30 and May 2, but deriving new tnal values for May 1 and 3. The coefiacients^i' and ^ i , s i ' i ' ' " " weie recomputed on the second approximation for greater accuracy. The labor involved in these computations was very great; the results obtained are given in the following tables: T A B L E I.—Values of A andp at each approximation. A P let approx. Assumed for Assamed for 2d approx 2d approx Ist approx 2d approx 2d approx April 29 2 194 0 734 30 2 358 2 358 2 337 0 745 0 745 0 751 May 1 1 983 2 25 2 327 0 75b 0 756 0 737 2 2 315 2.315 2 303 0 7b0 0 760 0 7b4 3 2 611 2.40 2 576 0 b65 0 730 0 690 - 

feOLAE E C L I P S E , M A Y 6, 1883. 83 T A B L E II.—Comparison of computed and observed solar intensities. A P R I L 29 Intensities.- Residuals (obs —comp.) Time Computed. ^ Observed I. II ni I. II. m. A M . 9 00 1 38 1 45 1 38 . . . — 0 07 o.do + 06 11 10 00 11 00 1 61 1 55 1 55 1 60 1 50 1.55 . . . . . . — .05 + .00 . . . . . . . . — 01 04 11.15 1 60 1 61 1.56 -c - - .00 + .05 . . . . 11 ^0 1 62 1 02 1 57 . . . + 01 + .06 . . . . 11 45 1 63 1 62 1 57 . . . — .03 + .02 . . . . 12 00 P M 1 59 1 62 1 57 . . . + . . . . 12.15 1 00 1 62 1 57 . . . — .02 + .03 . . . . — .02 03 12 30 1.30 1 59 1 41 1 61 1 .58 1 56 1 52 . . . . . . — .17 + 11 . . . . . . . . 2 10 1 35 1 53 1 47 - • — .18 — 12 . . . . •— 11 . . . . 2 30 3 00 1.33 1 40 L.50 1 43 1 44 1 37 . . . - - - - .03' + .03 . . . . A P R I L 30. A M 11.00 1.76 1.71 1 69 1 69 + 0 05 + 0.07 + 0 07 11 30 1 73 1 72 1 70 1. 71 1 72 1 72 1 71 1 71 + .01 00 + .03 + .02 11 45 1 72 1 72 1 71 1 71 .00 + .01 01 + + 01 01 12 00 P M + 12 15 1 70 1 72 1 71 1 71 — 02 — .01 — .01 3 00 1 44 1.54 1 50 1 50 — .10 — .06 — 06 3 30 1 34 1 45 1 40 1 41 — .11 — 06 — .07 4 00 1 24 1 33 1. 26 ,1 27 — .09 — .02 —- 03 1.07 1 15 1 02 1. 07 08 05 00 4 30 5 00 0 82 0 88 0 75 0 78 — .06 + .07 + 04 — + MAY 1 A M 7.00 0 80 -0.48 0 74 0 77 0 32 0 06 + 0 03 7 15 0 93 0 67 0 87 0 93 + .26 + .06 .00 1 09 0 83 0 97 1 05 + 26 + .12 + 04 7 30 •8.30 1 23 1.29 1 23 . . - + 06 + .00 . . - . 8 45 1 39 1 38 1 27 1 42 + 01 + 12 — .03 *9 00 1 37 1 44 1 31 07 00 9 30 1 47 1.56 1.36 . 1 . 54 - 09 + 11 . . — .07 . . 10 00 1 52 1.64 1.40 1 59 — 12 + 12 — .07 10 30 1 00 1 70 1 43 1 62 — .10 + 17 — 02 11 00 1 69 1 74 1 45 1 65 — 05 + 24 + 04 12 00 1 76 1.77' 1 47 1 67 — 01 + .29 + 09 P M — + 1 00 1 65 I 73 1 44 1 04 — 08 + 21 + 01 2.00 1 64 1 63 1 40 1 58 .01 24 + 06 + + ' Rejected on second approximation. 

84 MEMOIES O F T H E NATIONAL A C A D E M Y OP S C I E N C E S . T A B L E II.—Comparison of computed and observed solar intensities—Continued. MAY 2 Intensities - • Residuals (obs —comp ) Time Computed. Observed I II III. I ' II. m / A. M 7 00 0 79 1 Ob 0 88 0 89 — 0.27 — 0 09 — 0 10 7 40 1 08 1 33 1 21 I 22 — 25 — U — 14 8 00 1 28 1 42 1 32 1 32 — 14 — 04 — 04 10 00 1 61 1 68 1 64 1 64 07 .03 — 03 10.30 1 64 1 71 1 68 1 68 — 07 — .04 — 04 10 45 1 68 1 72 1 69 1 69 — 04 — 01 — 01 11 00 1 70 1 72 1 70 L70 — 01 00 .00 11 15 1 73 1 73 1 71 1 71 00 - + 0402 + 02 11 30 1 75 1 73 1 71 1 71 + 02 + 01 + 04 - 12 00 P M 1 73 1 74 1 72 1 72 01 + + .01 12 30 1 74 1 73 1 71 1.71 + .01 + 03 + 03 1 00 2 00 1 71 1 58 . 1 1 72 67 1 1 70 63 1 70 1 64 — 01 09 + 01 05 + _.01 — 06 2 30 1 48 1 63 1 59 1.59 — 15 — 13 — 11 3 00 1 68 1 58 1 52 1 52 + 10 + lb + .16 3 30 1 48 1 50 1 42 1 42 — 02 + 06 + 06 4 00 1 37 1 40 1 29 1 30 — 03 + 08 + 07 4 30 1 17 1 24 1 09 1 10 07 + 08 + 07 5.00 0 yO 1 00 0 80 0 82 — 10 + .10 + .08 MAY 3 - - A M 10 30 ,1 58 1 70 1 61 1 6b — 0 12 — 0 03 — 0 08 11 00 1 72 1.72 1 64 1 69 00 + 08 + .03 11 30 1 73 L73 1 66 1 71 00 + 07 + 02 12 P 00 M. 1 73 1 73 1 67 1 71 00 + 06 + 02 12 30 1 71 1 73 1 66 1 71 — 02 + 05 00 1 00 1 68 1 72 1 64 1 bfi — 04 + 04 00 1 .30 I 69 1 70 1 60 1 65 — 01 + 09 + 04 2 00 1.62 1 67 1 55 1 61 — 05 + 07 + 01 2.30 1 53 1 63 1 48 1 54 — 10 + 05 01 In the above table the columns I , I I , I I I of intensities and residuals refer to the first com- putation, with the assumed values of A and j?, the result of the first approximation, and the result of the second approximation respectively A n examination of the last column of residuals shows how nearly the second approximation represents the original observations. There are a few large residuals, but on the whole the agreement is very satisfactory. The lesulting values of the solar constant have been given m Table I , and show excellent agreement. Collecting them here, with the interval of time covered by the observations on each day, we have the following results: SOLAR CONSTANT. Date. Interval A April 29 9.00 a m to 3 00 P m 2 194 30 11 00 a ra to 5 00 P m 2 337 May 1 7 00 a. m to 2 00 P m 2 327 2 7 00 a m to 5 00 P m 2 303 3 10 30 a. m to 2 30 P- m. 2 576 Mean of aU, 2 347. Mean of April 30 to May 2, 2.322.