37° Dr. Herschel's Account of the Changes that have happened 
many particular circumstances must concur in explaining the 
phenomena of y Leonis as we have pointed out with « Gemi- 
norum, but that a very marked condition is added in our second 
double star, which requires an adjustment of velocities in y and 
x, which shall also fit the same solar motion that was used in a 
Geminorum. And this proves, that every additional double star 
which requires the same condition in order to have its appear- 
ances explained, will inforce the arguments which have been 
used, in a compound ratio. 
If, on the other hand, we have recourse to the simplicity of 
the known effects of attraction, and admit the two stars of our 
present double star to be united in one system, all the foregoing 
difficulties of accounting for the observed phenomena will vanish. 
Whatever may be the proper motion of the sun, the parallax 
arising from that cause will affect both stars equally, on account 
of their equal distance from the sun. The proper motion of 
y Leonis also may be in any direction, and of any given velocity, 
such as will agree best with astronomical observations; since 
the motion of a system of bodies will not interfere with the 
particular motion of the bodies that belong to it, so that our 
secondary star will continue its revolution round the primary 
one without disturbance. 
It will now be necessary to examine the observed angles of 
position, and to compare them with calculated ones; but, as 
there has been a change in the distance of the two stars, it is 
evident that, if they revolve in circular orbits, the situation of 
the plane of their revolution must be considerably inclined to 
the line in which we see the principal star. 
Let N F S P, Fig. 2 ,^ be the orbit in which x revolves about 
y placed in the centre. Suppose a perpendicular to be erected at 
