581 
of Edinburgh, Session 1871 - 72 . 
8th, The ratios of these velocities to those of the planets are 
several million times greater than the ratios of the gravities of the 
planets towards the sun, to the greatest resistance which secular 
observations allow us to suppose they experience. For example, 
[these velocities must be] some hundredfold a greater number of 
times the velocity of the earth, than the ratio of 190,000* times 
the gravity of the earth towards the sun, to the greatest resistance 
which secular observations of the length of the year permit us to 
suppose that the earth experiences from the celestial masses. 
CONCEPTION, which facilitates the Application of Mathematics to 
determine the mutual Influence of these Heavy Bodies and these 
Corpuscules. 
1st, Decompose all heavy bodies into molecules of equal mass, so 
small that they may be treated as attractive points in respect to 
theories in which gravity is considered without reference to its 
cause ; that is to say, each must be so small that inequalities of 
distance and differences of direction between its particles and those 
of another molecule, conceived as attracting it and being attracted 
by it, may be neglected. For example, suppose the diameter of 
the molecule considered to be a hundred thousand times smaller 
than the distance between two bodies of which the mutual gravita- 
tion is examined, which would make its apparent semi-diameter, 
as seen from the other body, about one second of angle. 
2d, For the surfaces of such a molecule, accessible hut imper- 
meable to the gravific fluid, substitute one single spherical surface 
equal to their sum. 
3d, Divide those surfaces into facets small enough to allow them 
to he treated as planes, without sensible error, [&c., &c.] 
Remarks. 
It is not necessary to he very skilful to deduce from these 
suppositions all the laws of gravity, both sublunary and universal 
(and consequently also those of Kepler, &c.), with all the accuracy 
which observed phenomena have proved those laws. Those laws, 
* To render the sentence more easily read, I have substituted this number 
in place of the following words : — le nombre de fois que le firmament con- 
tient le disque apparent du soleil.” 
VOL. VII. 
4 i 
