1902.] SNYDER — A NEW METHOD OF TRANSITING STARS. 201 



base of the transit instrument on a polar axis and within a limited 

 range drive the instrument to the diurnal motion by means of 

 clockwork, and in some undescribed manner keep the star bi- 

 sected so as to determine the meridian passage through electrical 

 signals automatically made. The plan admirably met the chief 

 difficulty of the varying rate of motion due to difference of decli- 

 nation, but was abandoned on account of the great mass to be 

 moved. 



It has to the writer, however, seemed likely that by applying a 

 powerful electric motor of strictly constant speed, and by using a 

 second electric motor with regulable speed for driving one element 

 of a differential gear which engages the shaft driven by the main 

 motor, or by several other electrical devices not requiring men- 

 tion, an equatorially mounted transit instrument can be driven to 

 stellar bisection and readily kept so adjusted. 



A second plan, " Neuer Vorschlag zur Vermeidung des person- 

 liclien Zeit-Fehlers bei Durchgangs-Beobachtungen," was proposed 

 by RepsoldMn 1889 and tested by Becker'^ in 1891 with moder- 

 erately favorable result A new form of micrometer, made for the 

 Madison Observatory by Repsold,^ was described in 1896, and with 

 the general plan of its construction the writer became acquainted 

 in the autumn of 1897. This specially designed and rather com- 

 plicated micrometer requires that s^ar bisection shall be main- 

 tained by twirling the micrometer shaft alternately v/ith each hand 

 of the observer. While this twirling is proceeding the ten elec- 

 trical contacts of a drum mounted on the micrometer screw deter- 

 mine as many records on the chronograph. This Repsold method, 

 while not lacking in ingenuity, seemed to the writer to labor under 

 the following defects : An alternating twirling motion of the mi- 

 crometer, even when communicated with the greatCbt adroitness, 

 is not approximately a uniform motion. The observer is attached 

 to the instrument by both hands, and is incessantly committed to 

 the most painful attention. Good results could hardly be secured 

 without the most prolonged and painstaking practice. Through 

 his special habit of twirling each observer must have a new form of 



^F. Repsold, Astron. A^ach., 2940, 1889, September. 



2 Prof. E. Becker, " Ueber einige Versuche von Durchgangs Beobachtungen 

 nach dem neuen Repsold'schen Verfahren," Astron. Nach., 3036, 1891, Marz. 



3"Neue ^Mikrometer von A. Repsold u. Sohne," Astron. Nach., 2>Z1h 1896, 

 Juli.: 



