380 Dr. Herschel’s Account of the Changes that have happened 
it will be ,04,18. This will show itself at the parallel of fin a 
direction of 25° 5' north preceding, the solar motion being in 
the opposite direction south following. But this parallax will 
only produce, in 20 years and 10 months, an apparent change 
of o // ,444 in f, and of o",355 in x ; and will separate the stars, 
instead of bringing them to a conjunction. 
( e ) A considerable advantage may be gained, by placing x 
at a little more than ^ the distance of f from O. For as, in the 
abovementioned time, this would make the effect of parallax 
upon it T' s l8, a conjunction should now take place. But then 
the stars, though very near each other, would not be quite in 
contact ; much less could one of them occasion an occultation 
of the other. The supposition also, that the small star should 
be only •§- of the distance of the large one from us, is not very 
favourable to the hypothesis. 
2 Serpentis. 
This double star has undergone a very considerable change 
in the angle of position, but none in the distance of the two 
stars. The 3th of September, 1782, an accurate measure of the 
position was 42 0 48' south preceding; and February 7, 1802, it 
measured 6 1° 27' south preceding. In 19 years and 355 days, 
therefore, the small star has moved, in a retrograde order, over 
an arch of 18 0 39'. 
Every argument, to examine the cause of this motion, which 
has been used with s Bootis, in the paragraphs from (a) to (z), 
will completely apply to this star ; from this we may conclude, 
that the most natural way of accounting for the observed changes, 
is to admit the two stars to form a binary system. In this case 
we calculate, with considerable probability, that the periodical 
