192 J. Wharton on determining the distance, ete. 
pared to say that they do so in any case: it is in fact asserted 
that the larger star is usually red and the smaller one blue. 
Supposing this train of thought to be sound, and that by ex- 
tremely careful observation a difference could be detected in the 
position of a variably colored star when it appears red, from its 
been found, which has a measurable change of position in one 
ine of vision, and let us assume that its extreme colors indicate 
a difference in the rate of arrival of light impulses (or in other 
words a difference in the velocity of the light arriving from that — 
star at the two periods), equal to 2uv, then the actual speed of the 
star in its orbit =v and as the orbital period of the star has been 
found =z, it follows that Pig is the real length of that diame- 
ter which is the measured angular distance between the two 
extreme positions of the star. Knowing the angle, and the 
oat of the base which subtends it, we have the distance of 
e star. 
nts. 
variable 
i pul 
ou less frequently. T I 
low roar in this case are facts whi 
light 
