Bicxerton.—On Partial Impact; 129 
is a well-known fact, that if a projectile revolyes on one axis at right 
angles to the line of motion, there is a tendency to move in a curve. 
(The full discussion of this phenomenon would occupy much time.) It is 
possible to show that this force at first would have considerable effect in 
rendering the orbits circular, but finally with the planets near the sun its 
effect may be to render the orbits more elliptical. All these forces, there- 
fore, tend to render the orbits more circular, but not as an average result 
to alter their mean distance from the sun. The larger masses would 
suffer less resistance in proportion than the smaller ones, and the general 
result would be, that if all started at the same distance the smaller bodies 
would be brought nearer the sun. It is easy to see that the centrifugal 
force and the attraction of nebulous mass would cause all the planets to 
travel approximately in the plane of the ecliptic, also why the sun’s equator 
so nearly approaches it, and generally, why the rotations of the planets on - 
their axes should bein the same direction. On the other hand, the pressure 
due to heat, the extreme want of symmetry of such a case of partial impact, 
combined with the original motion of rotation of the colliding bodies, if they 
had any, must all tell in the ultimate resultant motion, both orbital and 
axial. Almost certainly these forces would produce slightly inclined orbital 
planes, inclination of polar axes to these planes, and may as an extreme 
case produce a retrograde motion. It is also easy to see that the enormous 
atmospheres of those early days would effectually clear the bodies of all but 
very large masses of cosmical dust. 
The Asteroids. 
This fact appears of itself sufficient to show that the production of the 
asteroids must have been a subsequent event to the formation of the solar 
system. With respect to the asteroids, it is conceivable that the destruction 
of the planet which formed them may have been produced by a large 
meteorie visitant, with a high velocity. This hypothesis shows that such 
bodies may exist in considerable numbers. Such a mass might conceivably 
bury itself in another body, and when its motion of mass was stopped, its 
heat might be sufficient to produce a pressure of many thousand atmo- 
spheres. Such an explosion of developed gas might reasonably be expected 
to blow the body to pieces. It is generally considered that if the asteroids 
had been produced by the destruction of a planet, the fragments would 
have the same mean distance from the sun, and would pass the same points 
in their orbits where the destruction occurred ; which is contrary to the 
observed motions of these bodies. The hypothesis that they are pieces of a 
planet is therefore not generally accepted ; but these assumptions are only 
true if the velocity remain the same, the eccentricity of the orbit the same, 
and there is no resisting atmosphere. The first of these assumptions ig 
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