84. Mr. Mossotti on the Constitution of the 
to the other, a circle of pale confused light will appear to be - 
projected or painted on the vault of the heavens. 
The structure of the sidereal system in which we are placed, 
according to the idea we have just formed of it, agrees as far 
as appearances go with the principles of geometry and per- 
spective, but it is necessary besides to verify whether this struc- 
ture is in accordance with the laws of mechanics, with the 
conditions of a system possessing the property of preserving 
itself unaltered in the course of time. The attribute of long 
conservation is a character which the Author has impressed 
on all the wondrous bodies of the heavens: 
“*Ccelestia semper 
Inconcussa suo volvuntur sidera lapsu *.” 
Analogy leads us to believe that the Newtonian law of at- 
traction which acts between all material particles of which 
the bodies in our planetary system are formed, obtains equally 
among those of all other bodies scattered through the uni- 
verse: the proofs of the legitimacy of this induction by ana- 
logy we shall borrow from Herschel himself. We find in 
the heavens stars which appear single when seen by the naked 
eye, but which when examined with a telescope are found to 
consist of two or more stars, and which therefore are called 
double or multiple stars. In order that this apparent coinci- 
dence of two stars may take place, it is sufficient that they 
be placed very nearly in the direction of the same visual ray, 
but one of the stars may be thus situated at a much greater 
distance from us than the other. Now Herschel having ob- 
served several of these double stars, in order to determine the 
annual parallax of one of them, met with an unexpected phe- 
nomenon. He remarked that in the greater number of these 
double stars, one star, in the course of years, revolved round 
the other; or to speak more precisely, both revolved round 
their common centre of gravity. Each of these double stars 
constitutes therefore a peculiar system; the two stars are not 
approximately cn the same visual ray, but are really close to 
one another and attract each other powerfully, and the cal- 
culation of their motions affords sufficient proof that they obey 
the Newtonian law. The existence of a mutual attraction 
between the stars being thus proved, we necessarily conclude 
that they move; but a system of motions which shall remain 
unaltered in a long series of revolutions, does not appear re- 
concileable in a system of bodies, the masses of which are 
promiscuously large and small, attracting one another in the 
inverse ratio of the squares of the distances and situated in 
* Lucan, Phars., lib. ii, 267. 
