272 Mr. herschel on the proper Motion 
iiruated of all, fhould have a great increafe of right afcenfioiv 
and thefe deductions alio agree with the table. 
In the la ft place, a very ftriking agreement with the hypo 
thel'is is difplayed in Caftor and Pollux. They are both pretty 
well iituated, and we accordingly find that Pollux, for the 
lize of the ftar,. (hews as much motion in right afcenfion as 
we could expedt ; but it is remarkable, and feemingly contrary 
to our hypothecs-, that Caftor, equally well placed, {hews by the 
table no more than one half of the motion of Pollux. Now, 
if we recolledl that the former is a double ftar, confifting of 
two ftars not much different in iize, we can allow but about 
half the light to each of them, which, affords a ftrong pre- 
fumption of their being at a greater diftance, and therefore 
their partial fyftematical parallax, by the third theorem, ought to 
be fo much lefs than that of Pollux, which agrees wonderfully 
with obfervation *. Not to mention the great difficulty in 
which we ffiould be involved, were we to fuppofe the motion 
of Caftor to be really in the ftar : for how extraordinary muft 
appear the concurrence, that two ftars, namely thole that 
make up this apparently fingle ftar, fhould both have a proper 
motion fo exadtly alike, that in all our obfervations hitherto 
they have not been found to difagree a fingle fecond, either in 
right afcenfion or declination, for fifty years together ! Does not 
this feem ftrongly to point out the common caufe, the motion 
of the foiar lyftem ? 
* If the light of Caftor was exa&ly equal to that of Pollux, and the two ftars, 
which make up the former ftar, were perfectly of the fame fize, we might, on 
that account, fuppofe the diftance of Caftor from us to be to that of Pollux as 
^2:1; but Caftor is in fa<£t fomething lefs bright ; and this confideration, added 
to the former, will make it probable enough that its diftance may perhaps be 
double that of Pollux. 
With 
