28 
Mr. Christie on the effects of temperature on 
COS.^ ((p 0008293 29^ { .000829329 cos.® (p +.000000001 6 
+ .123 X (.0046908 14 + . 000829329 cos.'^Cp)*! = 0 ; . . . • (r) 
.000000001 6, being the value of ^ in all the values of (p 
p 
for which I had to compute ; and .123 the value of A . ^ already 
found : the upper sign to be used when A . ^ is plus, or when 
the observed temperature of the magnets is above the mean 
temperature to which the observations are to be reduced, and 
p 
the lower sign, when A * ^ is minus. 
This formula is not so ill adapted for calculation as it may 
at first sight appear, since for each value of (p it is only 
necessary to refer to the tables eight times to obtain the 
values both of Cp + A (p and Cp — A^ <p, or of (p^ and Cp^. 
The values of (p, in the observations in doors, being com- 
prised between 77° and 86®, I calculated the two following 
tables as the basis of the tables by which these observations 
were to be corrected, for the difference between the ob- 
served temperature of the magnets and the standard tem- 
perature. 
