360 Dr. Herschel's Account of the Changes 
Feb. 21 and March 4, 1802, was 31 0 38'. By five measures, 
taken in 1803 and the beginning of 1804, it was 3 X ° 54/ * and, 
June 3, 1804, by a very accurate measure, with an improved 
illumination of the wires, it was 32 0 30'. This gives a change 
of ii° 22', in 23 years and 14 days. 
It does not appear that the distance has undergone any per- 
ceptible alteration. 
As we have now the proper motion of this star in Dr. 
Maskelyne’s new Tables, we are enabled to enter upon an 
examination of the cause of the observed change; but first it 
will be necessary to mention, that in this and all the following 
stars, I have no longer supposed the solar motion to be directed 
towards x Herculis. A point at no very great distance from this 
star has been chosen, for reasons which it would lead us too far 
from our present subject to assign, and which are of no absolute 
consequence to it. The motion of the solar system, towards this 
assumed point, will produce an opposite parallactic motion, in 
every star that is not too far from us to be sensibly affected 
by it. 
That change of place which astronomers have established by 
observation, and which is called the proper motion of a star, either 
may agree with this parallactic motion, (in which case it will be 
only an apparent one, the star being really at rest,) or it may be 
directed to another part of the heavens, so as to differ from our 
parallactic motion. Whenever this happens, the star will have 
the following three motions : a real, a parallactic, and an apparent 
one ; the latter being a composition of the former two. 
That u Herculis is one of those stars which has these three 
motions, will appear thus: the parallactic motion which this 
star, from its magnitude and consequent proximity, must be 
