©20 Dr. Herschel on the Quantity 
u Orionis indeed have so little motion that there are but three 
stars in all the 36 that have less. But the situation of these 
bright stars, from their nearness, must be favourable to our 
perceiving their real motions if they had any, unless they 
were counteracted by some general cause that might render 
them less conspicuous. Now to suppose that the largest stars 
should really have the smallest motions, is too singular an 
opinion to be maintained ; it follows, therefore, that the appa- 
rently small motions of these large stars is owing to some 
general cause, which renders at least some part of their real 
motion invisible to us. But when a solar motion is introduced, 
the parallax arising from that cause will completely account 
for the singularity of these slow motions. 
If the foregoing argument proves the expediency of a solar 
motion, its direction is no less evidently pointed out by it. 
For if the parallax occasioned by the motion of the sun is to 
explain the appearances that have been remarked, it will fol- 
low, that a direction in opposition to the motion of Arcturus, 
will answer that end in the most satisfactory manner. That 
compression, for instance, which has been remarked in the 
motions of the stars moving toward the solar apex in Fig. 3, 
and which is so completely accounted for by a parallactic 
motion arising from the motion of the sun, points out the 
direction in which the sun should move, in order to produce 
this required parallactic motion. The expansion of the motions 
that are in opposition to the former is evidently owing to the 
same parallactic motions, which in this direction unite with 
the real motions of the stars ; and as, in the former case, the 
observed motions are the differences between the parallactic 
and real motions, so here they are the sum of them. 
