Page:Popular Science Monthly Volume 16.djvu/102

92 Then, by dynamical principles, we have—

Substituting these numbers in foregoing proportions, and performing the arithmetical operations, and we have—

In the case of the earth, we know that it is much smaller; being about $5/4$ instead of $1/undefined$. Hence, for Mars also, we should expect an ellipticity smaller than $1/undefined$; whereas, as we have seen, nearly all the measurements indicate a much greater ellipticity.

It is evident that a more rapid rotation of the planet would augment its ellipticity; hence the question naturally suggests itself: Might not this great ellipticity of Mars have been the result of solidification having taken place when his rotation-period was much shorter than it is at present? This explanation is not free from serious difficulties. For, if aqueous and aërial agencies were in action after solidification took place, they would have tended to make the shape of the planet conform to its new rotation-period.