One familiar with modern electrical theories knows that the present tendency is to include everything in the electromagnetic scheme. Maxwell started this when he promulgated the electromagnetic theory of light. Experiment by Kauffman on the beta rays of radium lead us to regard mass as electromagnetic. Hence it is very natural to try to explain gravitation as an ether-phenomenon. This would require that the ether be capable of supporting enormous pressure or tension. In the older views the ether was regarded as a very attenuated medium. Such an ether can hardly meet the demands. Many modern physicists regard the ether as very rigid and dense when compared with ordinary matter. See Lodge's "The Ether of Space." If we follow Sir J. J. Thomson, who regards all mass as mass of the ether we can calculate the density of the ether, for the mass of an electron is about grams and the volume is of the order of cubic centimeters; hence the density of the ether is or a million million times that of water. When we consider the rapidity with which an ether disturbance is transmitted we see that the rigidity should be very great compared with ordinary matter. Taking the density of ether as and the velocity of ether waves as cms. per sec. the rigidity will be of the order of dynes per sq. cm., since The intrinsic energy if due to rotational motion will be of the order of ergs per cubic centimeter, if we assume the velocity of rotation is of the order of that of light; since the energy mass times , where the mass of a cubic centimeter is grams and the velocity is cms. per sec. Hence the intrinsic energy and rigidity of the ether will probably meet the demands if we accept the views of ether and matter held by some of the greatest modern physicists.
If a falling body does not gather its energy from the ether where does it get it? Lift a ton to the height of 1,000 feet above the earth's surface and we have 2,000,000 foot-pounds of potential energy, or preferably a body that in returning to its original position will gather 2,000,000 foot-pounds of energy. Is this energy inherent in the body? Newton's letter to Bentley shows us that he was opposed to such a view. One thing is sure, there is no perceptible change in the mass and chemical composition of the body at the height of a thousand feet.
In the "Principia" Newton makes no attempt to explain gravitation, but in one of his optical queries he writes thus: "If the pressure in the medium is less in the neighborhood of dense bodies than at a greater distance from them, dense bodies will be drawn toward each other, obeying the law of gravitation if diminution of pressure is inversely as the distance."
Hooke, a contemporary of Newton and a man of great ingenuity,
- See Silliman, "Lectures," p. 5