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PROCEEDINGS OF THE AMERICAN ACADEMY 



postures. His setting circle is directly before him, his working list at 

 one side, and liis chronometer or telegraph-key at the other. But he 

 is liable to a troublesome personal equation ; and I am told that the 

 collimation cannot easily be made steady, owing to the great prism 

 between objective and ocular. The instruments are also very costly ; 

 so that, in this country, a construction is preferred which is nearer 

 like the ordinary observatory transit. Here the prismatic or diagonal 

 eye-piece takes the pla,ce of the " broken telescope," as the other con- 

 struction is technically called in German. The observer has to change 

 position, and is liable to a variety of petty annoyances thence arising. 

 Upon the whole, I think one construction is as good as the other for 

 practical purposes. 



The distribution of stars to be observed for time may often be im- 

 proved by employing one star within 10° of the pole to every group 

 of four or five time-stars. The latter will then be predominately south 

 of the zenith, but not exclusively so. Where the instrument is known 

 to be very firm and solidly mounted, and has a reversing apparatus, 

 the collimation may be determined by the pole-stars alone. The 

 double-group for Denver, as previously given, would be modified by 

 introducing the polars 39 Cephei Hevelii and 6 Ursae minoris Bode, 

 as follows : — 



INSTRUMENT REVERSED. 



