No. 6.| INTRODUCTION. CHRONOMETERS. XXXI 
If this last supposition should in some cases prove insufficient, the series 
(a) will give the means for further corrections. The accuracy aimed at in the 
reduction depends of course on the accuracy of the observations, but as this 
is manifestly not great no such refined corrections have been found necessary. 
Now 
or, neglecting the second term and multiplying by « 
la me (han) 
Similarly for another observation of the same phenomenon, made with a tele- 
scope of aperture A, at the moment T, 
Veet —1| a=} k (T—T) 
I(a,) —(4,) | e=8# 2-2. 
If the two observations have been made with the Planet at the distance 
and by subtraction 
4 
D’ instead of D, x is to be replaced by ap wv, and consequently if 
D\4 
i uLe ()* eA OY (4) 
‘AN? ALE 
a= ta — (4;) slgsisatvellertst (cl cc (5) 
then « may be found by the equation 
ae — CHEE —— Ea ary ot ons Ghee (6) 
expressed in the same units as w, T, — T, being given in seconds. 
As soon as # has been determined in this manner by pairs of observa- 
tions, every observed moment 7’ found by means of an aperture A’ at dis- 
