Page:The Solar System - Six Lectures - Lowell.djvu/148



would be the case if the present system had been formed by the collision of two bodies. For, when dealing with such masses, the elasticity may be considered small, and, in default of elasticity, the matter after the collision would be found chiefly near the scene of the catastrophe if the impact were in the line joining their centres. The collision in space of two bodies happening head on is, of course, one of which the chances are very small, and, were it not for another fact, might be dismissed from reasonable consideration.

This fact is the present constitution of the unattached particles of the system, the meteorites. As we saw in a preceding lecture, these fragments betray a previous habitat. Their character shows that they came from the interior of a great cooled mass which once had been intensely heated. They are therefore proof of the prior existence of a great sun, and that they should be now strewn in space makes the theory of a subsequent collision far less improbable.

If such a collision occurred, the fragments would be scattered more sparsely according to their distance from the scene of the catastrophe, and we may perhaps assume the law governing this sparseness to be the curve of probability,

$$ y=\frac{h}{\sqrt{\pi}}e^{-h^{2}x{2}}. $$