Biographical Memoirs Volume 66 (1995) / Chapter Skim
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Seth Carlo Chandler, Jr.
Seth Carlo Chandler, Jr.
Pages 44-79
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S CARTER SETH CARLO CHANDLER, JR., IS best remembered for his research on the variation of latitude (i.e., the complex wobble of the Earth on its axis of rotation, now referred to as polar motion)
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The recent development of very long baseline interferometry (V~Bl) has improved the measurement of Earth orientation, including polar motion, length of day, universal time (UTI)
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But contemporary researchers using high-speed digital computers and analysis techniques not even known in ChandIer's day have found it difficult to develop a better model of polar motion. Recognition of the sheer volume of the computations that Chandier performed by hand and the completeness with which he was able to characterize the complexities of polar motion (not to mention the vast quantities of computations in his research of variable stars, comets, and minor planets)
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His party also traveled by ship to New OrIeans to make longitude determinations, again using telegraph signals to synchronize the local clock with the Coast Survey's master clock. It was an exciting period in geodetic astronomy and the young Mr.
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The Chandler homes in Cambridge, Wellesley Hills, and Strafford all are still standing, and the latter two are still owned by his descendants. INVENTING THE ALMUCANTAR While Chandler worked at the Coast Survey he used an instrument called a zenith telescope to determine the astronomical latitude and longitude of stations.
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Encouraged by this success, he designed the larger aperture (100 millimeter diameter objective lens) instrument shown in Figure I
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. DISCOVERY OF POLAR MOTION About 1765 Leonharcit Euler, a Swiss mathematician studying the dynamics of rotating fluid bodies, developed equations that suggested the Earth might wobble slightly about its axis of rotation.
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There was some level of disagreement within the scientific community, which continues today, as to who should be credited with the discovery of polar motion, Kustner or Chandler. When the Royal Astronomical Society of London awarded Chandler the GoIc!
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LEARNING THE COMPLEXITIES OF POLAR MOTION Chandier continued to analyze historical observations and in IS92 (Chandler, IS92a) reported that it appeared the period} of the polar motion had changed, increasing from approximately twelve months to fourteen months, during the previous century.
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From page 54... ...
SECULAR MOTION OF THE POLE During the very same period that Chandler was doing the laborious computations required for him to formulate his two-component model of polar motion, and to use the model to correct historical observations (a subject to which we will return later) , he also became embroiled in an argument with George C
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For example, by rereducing zenith-tube observations made by the British astronomer Samuel Molyneux and zenith-sector observations made by the British astronomer James Bradley nearly two centuries earlier, Chandler was able to determine polar motion values for the period 1726 to 1731. Figure 2 is a plot of the results (ChandIer, 190Ic)
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. The beating of two components of such nearly equal frequencies but disparate amplitudes wouIcI generate a very distinctive pattern in the motion of the pole.
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But some fifteen years later, circa 1926, an event just such as Chandler had predicted did occur. Based on numerical analysis of seventy-eight years of polar motion observations by the International Latitude Service, Dickman (1981)
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VARIABLE STARS Chandler released his first catalogue of 225 variable stars in 1888. As a rigorous observer of variable stars, discoverer of many, and enthusiastic computer of the elements of their variations, he was personally responsible for the elements of 124 of the 160 periodic stars in this, the first of three, full-scale catalogues.
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From page 60... ...
Chancller also detected correlations between the periods of the variable stars and the average range of the variations of their brightness. For periods under two months, the maximum brightness could be expected to be about three times the minimum, for periods of four to eight months, maximum brightness was about thirty times the minimum, and for periods longer than eight months maximum brightness was sixty times the minimum.
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For the next several months the debate raged, fueled chiefly by Ritchie, in local newspapers and in the Astronomische Nachri~chten, where Pickering accused Chandler of personal animosity. In the supplement to his second catalogue, Chandler entered several variables in the southern sky based on examinations of the Harvard College Observatory photographs made at its Boyden Station in Arequipa.
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From page 62... ...
His values were too small by about a factor of two because he assumed much too high albedos, but until space probes visited other bocIies in the solar system a century later there was little information from which he could obtain better estimates. In 1898 the minor planet Eros (first called Witt's planet or planet DQ)
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THE TELEGRAPHI C CODE One of the many obstacles associated with astronomy that Chandler saw fit to tackle was the important task of telegraphic transmission of scientific data. "In astronomy," ChandIer stated, "where accuracy is of vital importance, the details of a message are such that they are of little interest to the ordinary operator, and afford no means of correcting mistakes by the context" (ChancIler, 18811.
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From page 64... ...
Observatories continued to track the motion of the pole without interruption even during the two world wars, but this activity was considered an operational requirement for treating geodetic and astrometric measurements, with little scientific importance or excitement. The discovery of polar motion was eventually reduced to a brief anecdote in which Chandler was generally described as a wealthy merchant from Boston, an amateur who had just happened upon polar motion.
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E and Seth Carlo Chandler, Jr.
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R Investigation of controversial polar motion features using homogeneous International Latitude Service data.
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Seth Carlo Chandler and the observational origins of geodynamics. In High-Prec~sion Earth Rotation and Earth-Moon Dynamics.
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:4243. On the methods of observing variable stars II, Science Observer 1 (8)
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Science Observer4~7-8~:60-62. Notes on some recently discovered variable stars.
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Astronomische Nachrichten 115~2749~:217-20. 1887 Note on an inaccuracy in the development of a differential refraction formula.
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Astronomicaliournal 8~188~:159. Catalogue of variable stars.
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:161-66. Contributions to the knowledge of the inequalities in the periods of the variable stars.
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:107-9. Contributions to the knowledge of the variable stars.
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Astronomische Nachrichten 132 (3161 ~ :283-86. 1894 On the observations of variable stars with the meridian-photometer of the Harvard College Observatory.
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:60-61. Revised supplement to second catalogue of variable stars.
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Astronomicaltournall6~374~:1078. Third catalogue of variable stars.
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: 1 60-62 . The areal velocities in the annual component of the polar motion.
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:79-80. On the assignment of the nomenclature and the formation of a new catalogue of variable stars.
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:227-28. 1904 Revision of elements of third catalogue of variable stars.
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