Motion of the Sun , and solar System. 245 
distance is 3 6° 41' 34". The opposite of this, or right ascension 
255 0 39' 5°"> an d north polar distance 36'° 41' 34", is what we 
are to assume for the required apex of the solar motion. 
When a star is situated at a certain distance from the sun, 
which we shall call 1 ; and 90° from the apex of the solar 
motion, its parallactic motion will be a maximum. Let us now 
suppose the velocity of the sun to be such that its motion, to a 
person situated on this star, would appear to describe annually 
an arch of 2", 84825, or, which is the same thing, that the 
star would appear to us, from the effect of parallax, to move 
over the above mentioned arch in the same time. 
To apply this to Arcturus, we find by calculation that its 
distance from the apex of the solar motion is 47 0 7' 6 " ; its 
parallactic motion therefore, which is as the sine of that dis- 
tance, will be 2", 08718; and this, as has been shown, is the 
apparent motion which observation has established as the proper 
motion of Arcturus. 
In the next place, if we admit Sirius to be a very large star 
situated at the distance 1,6809 from us, and compute its elon- 
gation from the apex of the solar motion, we shall find it 
138° 50' i4",5. With these two data we calculate that its pa- 
rallactic motion will be — j = sp = 1", 11528 ; and this also 
agrees with the apparent motion which has been ascertained 
by observation as the proper motion of Sirius. 
Now since, according to the rules of philosophising, we 
ought not to admit more motions than will account for the 
observed changes in the situation of the stars, it would-be 
wrong to have recourse to the motions of Arcturus and Sirius, 
when that of the sun alone will account for them both; and 
this consideration would be a sufficient inducement for us to 
