﻿188 



INDIANA UmVEESITY STUDIES 



Several methods were used in making these observations. 

 Observations were taken of 76 transits of stars on the equator 

 on three different nights; 72 transits of stars passing near the 

 center of the field with the telescope set at -10 degrees dechnation 

 on one night; of 142 observations on ^ Ursae Minoris on two nights. 

 Nine sets of observations were made on as many different nights, of 

 the difference of declination of stars 37 and 38 in the Pleiades; 

 84 observations on 51 Cephei on one night. 



Temperature affects the screw value by changing the absolute 

 length of the s.crew, and by changing the focal length of the tele- 

 scope. The effect of these two changes on the screw is very small 

 and may be taken as proportional to the change in temperature. 



If Ro = the value of the screw for temperature To 

 R = the value of the screw for temperature T 

 X = the temperature coefficient 



Then 



Ro = R + R {r-ro)x. 



= R [l + (T-To)x]. . ■ 



Let be an assumed value of Ro, and y be the correction to Ri, then 

 R,+y=R [l+(T-To)x] 

 Ri+y=R+R{r^ro)x 

 -Rir-ro)x+y-(R-R,)=0. 

 Using this last as the equation of condition, the most probable value 

 of the screw was computed. This theory is developed in Chauvenet. 



Below is tabulated the results obtained from time to time, of 

 the value of the screw: 



Date. 



Method. 



No. Ob- 

 servations. 



Temp. 



R. 



Seeing. 



1906, Sept. 6 



^ Ursae Minoris 



18 



75.5 



11.5327" 





1906, Sept. 6 





26 



75 



11.5431 





1906, Sept. 7 





26 



76 



11.5386 





1906, Sept; 7 



« ■ a 



31 



77 



11.5376 





1906, Sept. 7 



a u 



m 



76 



11.5305 





1906, Dec. 3 



l\hoi 37 and 38 Pleiades 



I 



33 



11.5333 



Fair. 



1906, Dec. 12 



a a 



1 



44 



11.5158 



Hazy. 



1907, Feb. 2 





1 



26 



11.5170 



Poof. 



1907, Feb. 8 





1 



29 



11.5371 



Good. 



1907, Feb. 9 





1 



37.5 



11.5163 



Good. 



1907, Feb. 16 



51 Cephei 



84 



43 



11.5325 



Good. 



1907, Mar. 5 



of 37 and 38 



1 



39 



11.5338 



Unsteady 



