r 20-5 D 
IX. On the Quantity and Velocity of the Solar Motion . By 
William Herschel, LL. D. F. R. S. 
Read February &f, 180b. 
The direction of the solar motion having been sufficiently 
ascertained in the first part of this Paper,* we shall now* 
resume the subject, and proceed to an inquiry about its 
velocity. 
The proper motions, when reduced to one direction, have 
been called quantities, to distinguish them from the velocities 
required in the moving stars to produce those motions. It 
will be necessary to keep up the same distinction with respect 
to the velocity of the solar motion ; for till we are better 
acquainted with the parallax of the earth’s orbit, we can only 
come to a knowledge of the extent of the arch which this 
motion would be seen to describe in a given time, when seen 
from a star of the first magnitude placed at right angles to 
the motion. There is, however, a considerable difference be- 
tween the velocity of the solar motion and that of a star ; for 
at a given distance, when the quantity of the solar motion is 
known its velocity will also be known, and every approxima- 
tion towards a knowledge of the distance of a star of the first 
magnitude will be an approximation towards the knowledge 
of the real solar velocity ; but with a star it will be otherwise ; 
for though the situation of the plane in which it moves is 
* Phil. Trans, for 1805, page 231. 
