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. 53 M A Y 9, 1883. Anemometer. Barometer Thermometer a u Clouds Weath( Rel hu Wind Observed Reduced Hour t Dry Wet reading reading. A M 7 00 81 29 867 29 91 79 0 76 5 91 240 5 E Cloudy 10 str Miuimuni, 78 0 Special observations m connection, with Solar Eclipse, May 0, 1883. Barometer Thermometer a a i Clouds J3 Observed Reduced a I reading reading Drv. Wet I A. M 10 00 649 E 10 05 650 E. 10 10 651 E 10 15 83 29 955 2!) 987 84 4 79 9 81 651 E Clear 2 cum 10 20 ()52 E 10 25 653. E 10 30 942 971 84 5 80 1 81 654 0 E Clear 2 cum in horizon 10 35 654 5 E 10 40 936 965 84 0 79 9 82 655 0 E Fair 3 cum 10 45 656 0 E 10 50 656 7 E 10 55 657 3 E. 11 00 84 915 944 83 5 78 4 78 658 1 E 11 05 659 0 E 11 10 920 945 83 0 78 5 80 659 6 E. Clear 2 cunr 11 15 912 937 660 2 E 11 20 902 927 82 7' 78 4 83 661 0 E Fair. 3 cum 11 25 907 928 661 7 E 11 32-11 37 a m total phase of eclipse 11 40 663 7 E 11 43 903 935 82 0 77 5 82 E. Fair 4 cum 11 45 664 4 E 11 50 908 940 82 2 77 7 81 6(55 0 E Fair 3 cum 11 55 665 7 E 12 00 907 939 82 2 77 8 81 666 3 E Fair 4 cnm p M 12.05 667 0 E 12 10 903 935 83 0 78 1 79 667 5 E Cloudy 7 cum 12 15 668 3 E 12 20 887 916 82 8 77 9 80' 669 0 E F.air 5 cum 12 25 669.9 E 12 30 29 878 29 903 8J 7 78 1 78 670 3 E Clear 2 cum 12 35 84 0 78 5 77 671 E Clear 2 cum 12 40 671 E 12 45 672 E. 12 50 29 868 29 889 84 4 78 9 76 672 E Clear. 2 cum 12 55 673 E 1 00 29 863 29 888 84 8 79 2 78 674 2 E Clear 2 cum 1 05 674 7 E 1 10 675 3 E 1 15 87 29.843 29 860 85 0 78 9 74 676 0 E Clear 2 cum. Mtseellaneom.—Minimum during eclipse, 81 4. Maximum before eclipse, 84 6, at 10 30 a m , when partial eclipse had been i n progress twenty-six minutes. Maximum after ecbpse, 85 2, at 1 15 p in , five minutes before last contact. T h e temperature remained ahnost statiouaiy until after 2 00 p m 11.10 a m , color of sky bluish, but greenish about the horizon. 

54 MEMOIRS O F T H E NATIONAL A C A D E M T O F SCIENCES. Condensed meteorological summary. Temperature 7 a. m 12 m 9p m . Date Rain- Red'd Air Rel Rel. Red'd Air fall. Mm Max Mean Red'd Air Rel bar temp. hum bar. temp. hum bar temp hum 1883 Incheg. April 25 78 2 88 2 83 2 29 95 8L9 82 29 93 86 0 74 29 96 82.2 82 'i 26 80 8 87 8 84 3 99 82 8 80 93 87 2 70 98 79.2 88 0 3 27 78 1 88 3 8:5 2 .96 82 0 80 .92 87 2 74 90 81 6 80 28 79 2 89 3 84 2 93 79.9 85 87 87 2 72 91 82 0 80 29 77.7 88 83.0 91 82 2 79 84 87 9 70 87 82 3 76 0 30 79 5 88 83 8 89 82 8 83 .84 86 8 73 .90 82 0 82 May 1 80 2 87 83 9 92 82 8 75 87 86.5 67 93 81 5 78 2 80 2 84 4 94 82 0 72 87 87 8 66 .94 81 0 74 0 3 76.2 82 2 29 97 81 78 29 89 86 9 66 .97 78.0 88 4 72 4 84 5 78 4 30 03 74 99 30 00 81 8 75 98 76 0 94 i*^ 5 75./4 84 3 79 8 29.99 80 88 29 94 84 0 77 94 81 7 83 0 6 6 79 2 a85 5 a82 4 98 81 86 94 082 2 81 96 82.0 82 0 1 7 77 7 87 0 82 4 96 79 89 92 86 0 74 92 81.8 78 0 3 8 79 9 86 4 83 2 91 81 bO 86 8:5 6 81 90 81 8 83 (t) 9 78 0 91 79 0 91 \\i T o t a l rainfall 7.5 a E c l i p s e caused lower reading than i t would have reached ' Estimated tin.apprcciablo t E n t e i e d undei 4th I Estimated on A p n l 23 Wind velocities. HOURLY MOVEMENTS IN MILES. Apul 27. April 30 April 28 Apnl 26 May 1. May 2 May 5 May 4 CO Hour •a PI P. A M b 00 to 7 00 . - 8 4 5 0 - - 3 9 7 00 to 8 00 7 1 10 1 4 5 b 4 4 2 7 7 7 8 2 8 5 4 6 7 8 00 to 9 00 8 4 7 6 7 2 5 7 5 9 7 1 7 1 3 7 5 3 b 7 9 00 to 10 00 5 2 9 7 7 1 5 6 4 2 8 0 5.5 5 7 9 1 7 6 10 00 to 11 00 7 7 7 6 4 0 5 7 4 4 8 5 2 9 6 0 5 6 8 0 11 00 to 12 00 6 9 6 4 3 6 5 9 3 9 7 7 3 0 6 5 6.4 9.2 P M - 12 00 to 1 00 7 6 6 9 2 9 5 7 10 6 6 4 2 3 4 5 7 0 6 2 1 00 to 2 00 7 6 6 3 2 8 5 0 9 8 7 1 0 8 4.0 0 7 6 5 2 00 to 3 00 6 9 5 7 5 7 3 b 9 9 6.7 -0 8 - - 0 4 5.5 3 00 to 4 00 4 3 5.2 5 5 - (i 6 - 1 6 - - 0 1 - - 4.00 to 5 00 2 7 5 1 6 2 - - 5 3 - - 2 6 - - 0 0 - - 5 00 to 6 00 5 9 4 6 5 8 6 6 0 0 Observations made on May 6 are given lu connection with the report upon the eclipse observations 

S O L A R E C L I P S E , M A Y 6,1883. 55 T O T A L MOVEMENTS AND H O U R L Y A V E R A G E S 9 p m to 7 a 111 fol- 7 a m to 7 a m fol- 7 a m. to 9 p m lowing day. lowing day Date Total Hourly Total Houily Total Hourly movement average. movement average movement average A p r i l 26 86 2 6 16 66 3 6 6:H 152 5 6 a5 27 90 9 6 49 56 8 5 68 147 7 6 15 28 7b 8 5 49 62 0 6 20 118 8 5 78 29 84 8 6 06 69 6 6 96 154 4 6 43 30 85 5 6.11 69 4 6 94 154 9 6 45 May 1 96 8 6 91 63 3 6 13 160 1 6 67 2 42 4 3 03 18 } 1 81 60 7 2 53 3 75 8 5 41 17 0 1 70 92 8 3 87 4 41 1 2 94 18 1 1 81 59 2 2 47 5 67 9 6 28 71 3 7 H 159 2 b 63 6 116 0 8 29 72 5 7 25 188 5 7 85 7 131 2 9 37 81 1 8 11 212 3 8 85 8 137 4 9 81 70 1 7 01 207 5 8 65 6 05 OBSERVATIONS O F T H E RAIN BAND. The instrument used m these observations was a B R O W N I N G ram-band spectroscope. Two pointings were made at each observation, the first towards the horizon, the second to an altitude of about 4 5 ° , and the intensity of the band estimated ou a scale of 5. Alt Date Hour Sum Remarks 0° 45° A. M April 27 8 00 4 3 7 Rain-lines very distinct 28 7 00 4 3 7 Ou rain cloudsin north; r j i u - l i n e s d i s t i n c t 28 7 00 5 4 9 On clear sky in south, rain-linos indistinct 29 8 30 3 2 5 May 1 6 45 4 3 7 Raiu-lines distinct 1 7 30 4 3 7 Do 1 10.00 4 3 7 Do 2 8.00 4 3 7 Do 2 11 30 4 3 7 Do 3 7 00 4 3 7 Do 3 9 00 3 2 5 Rain-lines indistinct 4 8 00 4 4 8 Ou clouds, lines indistiuot 5 9 00 5 3 8 6 10 30 4 3 7 L i n e s indistinct b 11 10 3 2 5 Do METEOROLOaiCAL OBSERVATIONS DDMING TNE ECLIPSE The meteorological observations made during the stay at Caroline Island have been discussed in what precedes. I t remains to speak of the special observations made at the time of the eclipse, and to show what conclusions may be denved from them. Observations ot the barometer, dry and wet bulb thermometers, maximum and minimum thermometers were made by myself as opportunity offered during the progress of the eclipse. Observations of the conjugate thermome- ters, V I O L L E ' S conjugate bulbs, black and white bulbs m the sun, and of the direction and velocity of the wind, were made by Seaman J . C . H A R O L D every five minutes between 10.00 a. m. and 1.15 p. m. 

56 MEMOIES O F T H E NATIONAL ACADEMY OF SCIENCES. GENERAL WEATHER CONDITIONS. TJie sky during the early portion of the 6tli of May was partly cloudy, and the clouds threatened ram. Slight showeis occurred between 8 00 and 9.00 a. in., and a heavy shower at 9.15 a. m., after which the sky cleared. But at no tune during the day was the atmosphere free from a haze, which was apparent to the eye and also showed itself in the readings of the instru- ments. The relative humidity was above the average, being 81 per cent, at noon and 74 per cent at 2.00 p. m., and the radiation instruments gave lower readings than on other days, especially in the morning. Passing clouds prevailed during the day, but interfered only a httle with the observations of the eclipse. A t the first and fourth contacts there were no clouds in the vicinity of the sun. Immediately after the second contnct a light cloud passed over the eclipsed sun, and remained for a portion of the first minute of totality. There were no clouds during the remainder of the total phase, but immediately after third contact a cloud again covered the sun for forty seconds. Another cloud, heavier than its predecessors, obscured the sun for several minutes, beginning with the fifth minute aftei third contact. I t will be seen from the above that the observers were especially fortunate m the weather at the time of totality, but it should be remem- bered that at all times the atmosphere was hazy. The wind blew steadily during the day, aver- aging 8.3 miles an hour, as recorded by the anemometer 9 feet 7 inches above the ground. BAROMETRIC PRESSURE, The barometric observations show a slight, but well marked, rise in pressure during the eclipse. In order to determine whether this phenomenon has any real relation to the eclipse it is necessary to inquire whether a similar result might not have occurred on other days, and, also, what was the usual course of pressure between 10 00 a. m. and 1.00 p. m. The regularity of move- ment m the pressure from day to day renders such an inquiry possible, even though the observa- tions extend over a short period. On SIX days preceding the eclipse half-hourly observations of pressure were made between 10.00 a. m. and 1.00 p. m. These reduced are as follows: 10.00 10 30 11.00 11 30. 12 00 12 30 1 00 April 28 29 934 29 919 29 906 29 891 29 868 29 861 29 849 29 904 894 862 840 836 812 t 747 30 893 .889 .869 .853 .844 . . . .826 Mav 2 942 929 916 895 875 853 H4b 3 9b7 952 933 902 887 861 846 5 987 974 961 947 941 . . . 902 Me.m - - 29 938 29 92b 29 908 29 888 29.875 "29 855 29 844 * Missing values interpolated. t T h i s re.uliug probably should bo 29 797. 

Fig 16 BAROMETRIC CURVE DURING E C L I P S E Frtsstm Jl M to [Sea levdi WOO 10 IS 1030 1045 IIM 11 IS 1130 1146 1200 12 IS 12JO 12.43 100 US in. \—3000 \- 2999 — 29117 \—2996 2994 -2933 • 2992 - 2991 - 29 SO -29J9 •29.88 •29SP 2930 Barometric curve, M i i C Meau baroniotnc cui'vo (b days ) - • 29M 29J4 

Fig 17 TEMPERATURE CURVE DURING E C L I P S E Tune par Temp k , , I I I I I I I I I \-S70 '^^^ '^"'^^ '"'^'^ ''"^ ^''^ ^•'^ -^^^ ^ 3JS \-860 •sso \-840 830 h820 Obsunul tcmiiiratiirc Mny6 Mean tcinporutim) A])ril 2j-il-i\ 0 (omitting May 4 ) . —I I I \ I I 

S O L A R E C L I P S E , M A Y 6,1883. 57 The following table contains the reduced readings for May 6, and a comparison with values interpolated from the mean values above given. BAROMETRIC PRESSURE Mean of DitF minus Hour May 6 Diflf SIX days moan diff y A M 9 57 29 9?5 20 938 ' 0 047 — 0 001 10 15 10 30 987 971 932. 92() 055 045 + .007 003 10 40 9l.'-> 920 045 — 003 11 00 044 .908 .0.16 — 012 11 10 94:> 901"- 044 — 004 11 15 <)i7 803 039 — 000 11 20 ')27 805 032 — 016 11 25 928 bOl 037 — Oil 11 43 935 HS2 053 005 11 50 12 00 040 9,19 879 875 061 064 + H- 013 016 P M 12 10 01") 868 067 + 019 12 20 12 30 916 001 8(.2 855 054 048 + 006 .000 12 50 880 848 041 — 007 1 00 888 844 0 044 — 004 Mean diff 0 048 - The above tables show that on all days but May 0 there was a steady fall in pressure, and therefore the observed rise on that ibij was peculiar to the day. Tbe last column of the second table indicates a more rapid fall than the aseiage during tbe first partial phase, and also that tbe time of tbe maximum difference from tbe avoiage course occurred at about 12.10 p. m., or thirty- three minutes after the close of tbe total iibase. Tbe highest reading was recorded at 11.60 a. m., or thirteen minutes after the end of totalitj. While the rise in pressure was small, being at its maximum only 0.019 above the average value, it I S yet greater than the oirors of observation. The instrument used can be read accu- rately within 0.005, and as it was licpt at iiearlj uniform temperature during the period of obser- vation, the possible uncertainty from failuie of tbe attached thermometer to record thie tempera- ture of the instrument can scarci'l.\ amount to 0.005. On the supposition that the errors have the same sign, there still remains 0 01 inch which is not accounted for, and the observed progression depends upon six or more obser\atioiis. I t is not ditticult to imagine also that the inflow of air towards tbe path of the shadow might be sufBcrent to cause an increased pressure susceptible ot measurement by a sensitive barometer. TEMPERATURE. The effect of the eclipse in vodnciiig tli(i temperature of the air may be shown by comparing the thermometric readings with those of other days. The mean values of-the observed tempera- ture, April 25 through Ma.> 5, omitting tbe rainy day, May 4, are as follows: Hour Degrees. Hour Degrees. A M A M. 7 00 81 9 11 00 86 3 8 00 83 4 12 00 86 7 P M 9 00 84 9 1 00 85 7, 10 00 85 5 2 00 85 9 The following table contains a comparisoa between the observed readings on May 6 and values interpolated from the above averages. I t will be seen from the colmnn of differences that at 9.57 a. m., before the beginning of the eclipse, the observed reading was lo.9 below tbe aver- S.'Mis. 110 8 

58 MEMOIRS O F T H E NATIONAL A C A D E M Y O F S C I E N C E S age, and that at 1 30 p m , after its close, it was 0 8 below Interpolating fioni these values the differences which would probablj have existed at the time of the eclipse had there been no unusual phenomenon, we ha^e the v.alues of the effect of the eclipse given in the last column under the heading " Depression " AIR TEMPERATURE Regular do Depres Hour May 6 Average Diff c n ase for the d i v Bion A M 0 o 0 0 o 9 57 83 6 a5 5 1 9 1 9 0 0 10 15 84 4 85 7 1 3 1 8 -0 5 10 10 84 5 85 9 1 4 1 7 -0 3 Maxiniuin, 8 4 ° 6 10 40 84 0 86 0 2 0 1 () 0 4 H 00 83 5 86 ^ 2 8 1 5 1 { 11 10 83 0 86 4 3 4 1 5 1 9 11 20 82 7 86 4 3 7 1 4 2 3 11 4) 82 0 86 6 4 6 1 3 3 3 } Minimum, 8 1 ° 4 , maxi 11 50 82 2 b6 6 4 4 1 3 i 1 I nuiin depiession, 1° 9 12 00 82 2 86 7 4 5 1 2 3 3 P M 12 10 a3 0 80 5 3 5 1 2 2 3 12 20 82 8 86 4 i 6 1 1 2 5 12 30 83 7 86 2 2 5 1 I 1 4 12 35 84 0 86 1 2 1 1 1 1 0 12 50 84 4 85 9 1 5 1 0 0 5 1 00 84 8 85 7 0 0 0 9 0 0 1 15 85 0 85 8 0 8 0 8 0 0 Maximum, 8 5 ° 2 1 30 85 0 85 8 0 8 0 8 0 0 The maximum depression of temperature was tlioretore only about 4 ° , but this was suflBf lent to reduce the temperature to a value 0 ° 1 lower than it had been at 7 00 a m on the same dav, and 0° 0 lower than it was at 9 00 p ni HUMIDITY The effect of the eclipse upon the humidity may be found by comparing the psychrometric reaflings taken duung the piogrcss of the eclipse with those of other days The following table gives the result of this compaiison, the values in the'column headed "average" being deduced from the mean values from April 25 through May 5, omitting May 4 The " regular decrease for the dav " is interpolated from the observed differences at 9 57 a m and 2 00 p m RELATIVE HUMIDITY R e g u l a r de Hour Maj 6 Average Din 1 rease for Diff the day A M 9 57 85 74 9 9 0 10 15 81 74 7 8 -1 10 30 81 73 8 8 0 10 40 82 73 9 7 2 11 00 78 72 6 7 -1 11 10 80 72 8 7 1 11 20 83 71 -12 7 5 11 41 82 71 11 6 5 11 50 81 70 11 6 5 12 00 81 70 11 6 5 P M 12 10 79 70 9 6 3 12 20 80 70 10 6 4 12 30 78 70 8 6 2 12 35 77 70 7 5 2 12 50 76 70 6 5 1 1 00 78 70 8 5 3 1 15 74 70 4 5 -1 1 30 74 71 3 4 -1 2 00 74 71 3 0 The above table indicates an increase m the iclativc huiniditj during the eclipse, reaching per cent 1. 

Fig 18 CURVE OF R E L A T I V E H U M I D I T Y DURING ECLIPSE nelaUve Jl M 1000 10 IS 10 SO 1045 1100 1115 1130 U 45 IZMO 1215 1230 1Z45 100 115 ss ?0 Obsorveil i-oliUiM) Immiditj "Mij 6 — Mean Imiiii(lit\ Apnl So-'NH^ fa omi(hii„ lln^ 4 ) —