200 SNYDER — A NEW METHOD OF TRANSITING STARS. [April 4, 

 A NEW METHOD OF TRANSITING STARS. 



BV iMONROE B. SNYDER. 

 {Read April 4, 1902.) 



The method of observing transits of stars, here to be described 

 in a preliminary and general manner, consists in driving the mi- 

 crometer screw and hence micrometer thread of a transit instru- 

 ment by means of an electric motor at the uniform speed pertain- 

 ing to any given declination, at the same time that the observer by 

 secondary adjustment secures and maintains accurate bisection of 

 the star, while given positions of the screw and hence thread are 

 automatically recorded on a chronograph. 



It is now more than four years since the writer described the 

 method to his associates interested in astronomical observation. 

 In the autumn of 1899 this plan of electrically driving the transit 

 thread was also mentioned to Professors Wadsworth and Morley 

 and at some length discussed with the latter. Working drawings 

 of the special instrument which at present gives concrete expres- 

 sion to the method were completed in September, 1900. The 

 "electrical transiter," or more simply *Uransiter," as for brevity 

 the new device has been named, was mounted on the small me- 

 ridian circle of the Philadelphia Observatory in February, 190 1, 

 and there subjected to many tests and improvements since. The 

 demands on the writer's time have, however, not permitted that 

 singleness of devotion which the transiter and its interesting 

 method should receive, and it does not, therefore, seem desirable 

 any longer to withhold a preliminary communication on the 

 subject. 



The fundamental idea of moving a transit micrometer wire by 

 means of clockwork synchronously with the star's motion was 

 proposed in 1865 by Braun.^ But to Repsold is due the persistent 

 pursuit of the idea that personal equation can be banished from 

 transit observations by mechanical methods. And although his 

 practical solutions of the problem have hardly proved adequate, 

 they have stimulated and permitted serious efforts on the part of 

 observers. 



The first suggestion of Repsold, ^ made in 1888, was to mount the 



1 Dr. Carl Braun, Das Fassagen-AIikrofneter^ Leipzig, 1865. 



2 F. Repsold, «' Durchgangs-Instrument mit Uhrbewegung," Astron. Nach.y 

 2828. 



