244 Herschel on the Direction of the 
position of other double stars point out, and this cannot be 
probable. 
Direction of the solar Motion. 
From what has been said, I believe the expedience of ad- 
mitting a solar motion will not be called in question ; our next 
endeavour therefore must be to investigate its direction. 
To return to the before mentioned intersections of the arches, 
in which the proper motions of the stars are performed, I shall 
begin by proving that when the proper motions of two stars 
are given, an apex may be found, to which, if the sun be sup- 
posed to move with a certain velocity, the two given motions 
may then be resolved into apparent changes, arising from 
sidereal parallax, the stars remaining perfectly at rest. 
Let the stars be Arcturus and Sirius, and their annual proper 
motions as given in the Astronomer Royal’s Tables. 
When the annual proper motion of Arcturus, which is 
— 1",2 6 in right ascension, and -fi",72 in north polar distance, 
is reduced by a composition of motions to a single one, it will 
be in a direction which makes an angle of 55 0 29' 42" south- 
preceding with the parallel of Arcturus, and of a velocity so as 
to describe annually 2",o87i8 of a great circle. 
The annual proper motion of Sirius, — 0^,42 in right ascen- 
sion, and -j- i // ,04 in north polar distance, by the same method 
of composition, becomes a motion of 1", 11528, in a direction 
which makes an angle of 68° 49' 41" south-preceding with the 
parallel of Sirius. 
By calculation, the arches in which these two stars move, 
when continued, will meet in what I have called their parallactic 
center, whose right ascension is 75 0 39' 50", and south polar 
