OF ARTS AND SCIENCES. 



1G3 



The single polar iu the first position (39 Cephei IT.) is proUalily 

 quite sutlicient to give equal accuracy in azimuth witli the two (P. and 

 3 Draconis) in the former list, especially as 4 Draconis II. is now 

 replaced by a close polar. The intervals are now a little closer in 

 some cases than before, as the instrument is expected to be easier 

 reversed by a machine, and the lines in the focus to be nearer to- 

 gether. 



Additional tirae-stars may also be inserted, namely : — 



But this would involve (as indeed the close polars do) much extra 

 computation. 



The fashion in Germany has been, lately, to select a list of stars to 

 be observed regularly, night after night, at both stations ; thus freeing 

 the results more exactly from errors in the star-places, and, indeed, 

 supplying observed right ascensions of great accuracy. This plan 

 would be excellently well adapted for such observations as those be- 

 tween Denver and Pueblo, which are not far apart in longitude ; but 

 in much American work the distances are too great, and the use of the 

 telegraph-lines too precarious. Good star-places are common enough, 

 if we have them all collected in a convenient place ; and this is done in 

 the German catalogue mentioned, and, when that has not enough, in 

 my own catalogue of 981 stars, which is soon to be doubled in extent, 

 60 as to include the zone between 10° and 70° of declination, instead 

 of 30° to 60° only. 



The young observer should by no means fail to accustom himself to 

 the eye-and-ear method of observing. It is, as Leverrier has remarked, 

 a better discipline than the chronographic. It is somewhat less accu- 

 rate : but one who can use it skilfully can always adapt himself to a 

 chronograph with ease ; and, on the other hand, if the chronograph 

 breaks down, or any trouble with it occurs where help cannot be got, 

 the eye-and-ear observer is more independent than the mere chronog- 

 raphist. For this reason, I have never allowed a pupil to use a 

 chronograph till he had mastered the elementary practice of the other 



