342 HISTOKY OF ASTRONOMY. 



Mr. Walker, the error in the mechanical part of imprint- 

 ing a date on the automatic clock register, and in reading 

 off the record, need not exceed a hundredth part of a 

 second. Mr. "Walker estimates that a transit over one 

 wire, printed by the new method, is worth four wires 

 observed by the old method. 



Another advantage of the new method of observation 

 arises from the increased amount of work which can be 

 done in a given time. Fifteen seconds is the ordinary 

 equatorial interval for the wires of a transit instrument. 

 In the new method of observing, the equatorial intervals 

 may be reduced from fifteen to two seconds, or even to 

 one and a half. In this manner the number of bisections 

 in a single culmination of a star may be multiplied ten 

 fold, making a gain of forty fold by the new or automatic 

 method. This is the estimated gain from the multipli- 

 cation of transits over wires, and the superior precision 

 of each. There are, however, other circumstances which 

 detract from this advantage, such as the time required to 

 prepare the apparatus for observation, to transcribe the 

 printed record into figures, etc. 



Before, however, the full advantage of this method 

 could be realized, some practical difficulties remained to 

 be overcome, of which the most important were the two 

 following : 



1st. It was essential to the accuracy of the new method 

 that the fillet of paper, or whatever might be the surface 

 upon which the dots were registered, should be made 

 to advance with perfectly uniform motion ; and 



