3 66 Dr. Herschel’s Account of the Changes that have happened 
revolution of the small star round Castor, will be about 342 years 
and two months. 
y Leonis. 
Our foregoing discussions will greatly abridge the arguments 
which may be used, to show that this star and its small com- 
panion are also probably united in forming a binary system. 
But, in order to give more clearness to our disquisition, we shall 
follow the arrangement which has been used with a Geminorum, 
and prefix the same letters to our paragraphs. Then, if any 
one article should appear to be not sufficiently explained, we 
need but turn back to our first double star, where the same 
letter will point out what has already been said more at large 
on the subject ; and an application of it may easily be made. 
The distance of the stars y and x , as I shall again call the 
small one, has undergone a visible alteration in the last 21 
years. The result of a great number of observations on the va- 
cancy between the two stars, made with the magnifying powers 
of 278, 460, 637, 840, 932, 1504, 2010, 2589, 3168, 4294, 
5489, and 6652, is, that with the standard power and aperture 
of the 7-feet telescope, the interval in 1782 was £ of a diameter 
of the small star, and is now With the same telescope, and 
-a power of 2010, it was formerly i of a diameter of the small 
star, and is now full 1 diameter. In the years 1795, 17 96, and 
1798, the interval was found to have gradually increased; and 
all observations conspire to prove, that the stars are now \ a 
diameter of the small one farther asunder than they were for- 
merly. The proportion of the diameter of y to that of x, I have, 
by many observations, estimated as 5 to 4. 
The first measured angle in 1782, is 7 0 37' north following;* 
* In my second Catalogue of double Stars, (Phil. Trans, for 1785, page 48,) the 
