COMSTOCK — STUDIES IX ASTRONOMY 91 



Certain auxiliary quantities to be used in setting the in- 

 strument so as to find the stars to be observed are also 

 given in the tables. Their use will be understood from 

 the following precept: "At the sidereal time 6—^"' point 

 upon the pole star by means of its azimuth a' and zenith 

 distance z = H - {cp-\- y tan cp) and without changing the 

 azimuth of the instrument await the clock star at the 

 zenith distance z = p — z'-" 



The following two examples illustrate, respectively, the 

 application of the trigonometric formulas, equations (16) 

 and (27), and of Dollens ephemerides, to the reduction of 

 observations made with a very small universal instrument, 

 having an objective with a clear aperture of 35 mm, focal 

 length 373 mm, magnifying power of ocular 36 diameters, azi- 

 muth circle read by estimation to single seconds. In view 

 of the small dimensions and feeble power of the instru- 

 ment the agreement between the values of the collimation 

 constant c given by the observed times and the circle read- 

 ings is sufficiently satisfactory. 



The computation by the trigonometric formulse is so ar- 

 ranged that the values of U, m\ etc., may be obtained 

 either with or without the use of the <? terms. 



