302 Review of Recent Geological Literature. 
smallest." This illustrates the tendency of the earth toward the sun, 
the boy withdrawn from the south side comparing to the ether waves 
of mechanical force intercepted from the earth by the sun. No account 
is taken here, of course, of the tangential force which maintains the 
earth in its orbit, and prevents its flight direct to the sun. But it is 
obvious that when a sufficient number of other planets and suns, each 
intercepting waves of mechanical force that pass through the celestial 
spaces, are adjusted in proper relations about the earth when it starts 
on its journey direct to the sun, its path would be so modified that the 
endless circle of its orbit would be the result. 
The author, by various illustrations, shows this theory is sustained 
by astronomical arguments, and by the demands of the law of correla- 
tion and conservation of energy, and then enters upon a comparison 
of gravitation with light and heat. He notes first five resemblances, 
viz: 
1. Light is unquestionably a vibration or quivering of the universal 
ether. Gravitation must necessarily act through the same medium, 
from sheer want of any other, and just as necessarily by means of 
vibrations, as the ether can not act by actual transference of its sub- 
tance. 
2. Light diminishes in intensity as the square of the distance in- 
creases. Gravitation does the same, but with a marked distinction. 
3. Both light and gravitation are regarded by all as emanating in 
their incipiency from ordinary matter. 
4. The combined force of light and heat, and the force of gravitation, 
are both forms of energy convertible in turn into all the others. 
5. These two forms of energy, like all other forms, are subject to 
the laws of conservation and correlation. 
These resemblances justify a suspicion at least of a closer relation 
than has hitherto been accorded them. Notable contrasts are as fol- 
lows : 
1. Gravitation acts as powerfully at the poles as at the equator. 
Not so light and heat. 
2. Light diminishes as the square of the distance increases, only 
per unit of area, and not at all in quantity. It is spread out thinner, 
but it is not lost, and could all be reconcentrated by a convex lens. 
Not so gravitation. 
3. Light at any distance from a luminous body can neither be in- 
creased or diminished in quantity, but only dispersed by divergence, 
and is strictly limited in amount. Not so gravitation ; for gravitation 
is practically infinite. It handles Jupiter as easily as the earth or as 
any of the asteroids. It is everywhere, and in sufficient force to do 
any work required of it. 
4. Heat penetrates, as heat, but a comparatively short distance in 
the inter-stellar spaces. Even as light it fades out, when the distance 
is great enough. Not so gravitation, for the emanations from the fixed 
stars, which are infinite in number, penetrate to the earth as cold 
