﻿370 B. A. Gould — Determinations of Stellar Positions. »■ 



One of these plates contained forty stars. Bessel's memoir 

 upon the Pleiades, published in 1844, gave the relative posi- 

 tions of 54 stars, measured with the Konigsberg heliometer, 

 during the years 1829 to 1841. Six of these 54 do not belong 

 within the limits of the plate (which contains about one square 

 degree), and 10 of them are too faint for the photographic 

 record, so that 16 of Bessel's list are wanting ; but, on the other 

 hand, there are two additional ones, not observed by him. 



From this fact alone it may.be perceived that among the 

 great benefits which astronomy may be justified in expecting 

 from celestial photography, the accurate determination of mag- 

 nitudes does not find place. The chemical action of the stellar 

 light upon the film is so dependent upon the character of that 

 light that, in the absence of a correct knowledge of its composi- 

 tion, we are very easily deceived regarding the amount. Thus 

 one of Bessel's stars which was not recorded upon any of Mr. 

 Eutherfurd's plates is estimated by Argelander as of the mag- 

 nitude 8*0, and by Wolf as 7f ; while five are distinctly recorded 

 which Argelander calls 8-J or less, and eight which Wolf so 

 estimates. The spectroscope would doubtless show a deficiency 

 of the more refrangible rays in the light of the former, and a 

 preponderance of the same in that of the latter. 



This series of measurements by Mr. Rutherfurd, together 

 with the computations to which the results were submitted, 

 constitute, if I am not mistaken, the first application of the 

 photographic method to exact astronomical determinations. 

 And the investigation necessarily demanded especial care, both 

 for guarding the numerical results against sources of unsus- 

 pected error and for fixing the limits within which known the- 

 oretical errors would remain unappreciable. 



The importance of the successful application of a method so 

 different from all previous ones, and so full of promise, and also 

 the considerable time which would inevitably elapse before the 

 memoir could be printed, led me at the same time to commu- 

 nicate to the Astronomische Nachrichten, at Altona, some of 

 the resultant values. In a comparatively short note, written 

 about the middle of August, 1866, I gave for the ten most con- 

 spicuous stars of the Pleiades, after Alcyone, the corrections 

 derived from one of the photographic plates of March 10, for 

 the values, published by Bessel, of the position-angles and 

 distances from Alcyone in 1840; as likewise the average dis- 

 cordance found for a single measure. 



In the next following year the Academy had not the means 

 of printing its memors; and, as, in the mean while, Mr. Ruth- 

 erfurd had measured five more of the plates of the Pleiades 

 previously taken, as well as six additional ones taken in the 

 months of January and February, 1867, these were also com- 



