﻿B. A. Gould — Determinations of Stellar Positions. 369 



Aet. LXIII. — Photographic Determinations of Stellar Posi- 

 tions ;*' by B. A. GrOULD. 



It has been suggested that a short account of my work upon 

 stellar photographs for the attainment of accurate observations 

 might be acceptable to the astronomical section. My intention 

 had been to attend this meeting as a listener and learner only ; 

 but I comply with the suggestion the more readily, since by a 

 notable coincidence, I spoke upon the same subject in this 

 place just twenty years ago, this week. It is true that my 

 communication then was only an oral one and never reduced 

 to writing; for the successful establishment of the Atlantic 

 cable, of which I had received notice that day, called me away 

 suddenly, before the time fixed for the regular presentation; 

 but an elaborate written memoir upon the subject had been 

 presented to the National Academy, ten days previous, at 

 Northampton. 



The early history of celestial photography is demonstrably 

 and exclusively American ; and its use as a method of delicate 

 quantitative research is very markedly so. Without entering 

 upon the historical data, which are of easy access to every in- 

 vestigator, I may mention that No. 77 of the Astronomical 

 Journal contained nineteen photographic impressions of as 

 many different phases of the solar eclipse of 1854, May 26 — 

 the moment of each impression being given to the nearest tenth 

 of a second. These were taken at West Point under the direc- 

 tion of Professor Bartlett, of the U. S. Military Academy, and 

 form a part of his memoir, in which he also gives the distances 

 between the cusps, as measured by himself with the microm- 

 eter in the telescope. Ten years later, in 1864, Mr. Euther- 

 furd constructed the 11J inch photographic object glass which 

 has acquired so conspicuous a place in astronomical history ; 

 and with this, in addition to its other achievements, he obtained 

 sharp photographic stellar images with a definition previously 

 unknown, taking for the first time distinct impressions of stars 

 invisible to the naked eye — in fact, to the 8f magnitude for 

 white stars. 



After constructing a micrometer of great delicacy for the 

 measurement of these plates, he measured with this the relative 

 distances and position angles of the stars which they contained. 

 And in the spring of 1866, he kindly placed in my hands the 

 results* thus derived from three plates of the Pleiades, each con- 

 taining two impressions, taken on the evening of March 10. 



* Presented at the Buffalo meeting- of the American Association for the 

 Advancement of Science, August 20, 1886. 



