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climatic zonation, as I pointed out in 1916.
We are living today in the waning hemicycle of one of these abnormal glacial periods, and as a consequence have reconstructed much of the past geologic history, not upon the standard or typical pattern of the earth, but upon a markedly abnormal, short-lived and seldom occurring set of conditions which happens to be the one in which we are living.
UNIVERSITY OF MICHIGAN,
September 14, 1920.
7 W. H. Hobbs, "The Ferrel Doctrine of Polar Calms and its Disproof in Recent Observations," Proc. Second Pan-Am. Sci. Congress, Washington, 1915-16, sec. 2, pp. 185–187.
DISCUSSION OF A KINETIC THEORY OF GRAVITATION, II, AND SOME NEW EXPERIMENTS IN
(Plates V. and VI.)
BY CHARLES F. BRUSH.
(Read April 22, 1921.)
At the Minneapolis meeting of the American Association for the Advancement of Science I had the honor to outline "A Kinetic Theory of Gravitation," which is in substance briefly, as follows:
The ether is assumed to be endowed with vast intrinsic kinetic energy in wave form of some sort capable of motive action on particles, atoms or molecules of matter, and propagated in every conceivable direction so that the wave energy is isotropic. The waves are of such frequency, or otherwise of such character, that they pass through all bodies without obstruction other than that concerned in gravitation. Distribution of the ether's energy is uniform throughout the universe except as modified by the presence of matter.
Atoms or particles are imagined to be continually buffeted in all directions by the ether waves like particles of a precipitate suspended in turbulent water.
Each particle or atom of matter is regarded as a center of activity due to its energy of translation initially derived from the ether. There is continual absorption and restitution of the ether's energy, normally equal in amount; but the ether is permanently robbed of as much of its energy as is represented by the mean kinetic energy of the particle or atom. The particle or atom thus has a field of influence extending in all directions, or casts a spherical energy shadow, so to speak, the depth or density of the shadow varying with the inverse square of distance. The energy shadow of a body of matter is regarded as the sum of the shadows of its
1 Science, March 10, 1911; Nature, March 23, 1911. PROC. AMER, PHIL., SOC., VOL. LX, D, DEC. 20, 1921.
constituent parts. The energy shadows of two gravitating bodies interblend, so that the energy density between them is less than elsewhere, and they are pushed toward each other by the superior energy density, or wave pressure, on the sides turned away from each other.
At the April meeting of the American Philosophical Society in 19142 I presented a discussion of above theory which I commend to the attention of those interested in the general subject of gravitation-the greatest of all outstanding physical problems.
While it is easy to picture the formation of the initial energy shadow of a single body of matter, I have always found it difficult to account for the maintenance of such a shadow. But when we consider two or more bodies (and there can be no manifestation of gravitation without involving two or more bodies), there is no trouble in picturing the interblending energy shadows between them, and this is the essence of the theory under discussion.
That the ether really is endowed with vast intrinsic energy in some form or forms is the belief of many eminent physicists, and it seems to me highly probable that all energy has its source and destination in the ether; that is to say, that energy in all the various forms in which we observe it comes in some way from the ether and is energy of the ether.
In this connection I beg to propose the hypothesis that the ether is abstract energy-energy pure and simple, quite apart from anything else. If the quantum theory of energy is tenable, then we may perhaps regard the ether as a vast atmosphere of energy quanta in violent agitation possibly somewhat like the molecules of a hot gas, though almost infinitely finer grained.
In support of my contention that ethereal energy is the cause and essence of gravitation, I wish to emphasize particularly, what seems to me an obvious fact, that the energy acquired by a falling body comes from the ether, and is restored to the ether when the body undergoes negative gravitational acceleration. (See Discussion above referred to.)
For many years I have sought for some experimental method of attacking the gravitation problem, but without success until a few 2 Proc. Amer. Phil. Soc., Vol. LIII., No. 213, Jan.-May, 1914.
months ago. Study of the nature of gravitation is beset with unusual difficulties, because gravitation is ever with us and about us; it is the one universal phenomenon, and we can not escape from its influence can not obtain any outside point of view.
In this connection I have endeavored to study the nature of a magnetic field in the hope of finding something common to it and gravitation; because we can largely localize a magnetic field and study it. Have long regarded a magnetic field not as a static affair, but alive with pulsating ethereal energy possibly akin to that of a gravitation field.
This view finally led to the thought that the very minute negative permeability of many substances, known as diamagnetism, may also offer some appreciable resistance or obstacle to the gravitational energy flux through such substances, and thus affect their gravitation field.
But what will be the nature of such modification, if any? It seems highly improbable that there can be any absorption of ethereal energy by a diamagnetic substance, because this would almost certainly generate heat in it-it would normally be warmer than its surroundings. I have carefully tested bismuth for this effect and found no generation of heat. But there may be a very slight reflection of the ethereal wave energy from each atom or ultimate particle of a diamagnetic substance, which may perhaps be regarded as a scattering effect, possibly analogous to the scattering of light by a faint opalescence in an otherwise transparent body. This I thought should weaken the gravitation field between a diamagnetic substance and a small neighboring body, whereby the attraction between them would be less than between the same neighboring body and a nondiamagnetic or less diamagnetic substance of the same mass as the first diamagnetic substance.
I realize that there may be no real foundation for the speculations detailed above, though I now have much experimental evidence which appears to support them; but, if for no other reason, they are important because they prompted the following experiments and brought to light their surprising results.
The first experiments were planned to detect, if possible, a dif
ference between the gravitation field of a comparatively large mass of the metal bismuth, which is the most diamagnetic substance known, and the gravitation field of a similar mass of lead and of zinc, which are very much less diamagnetic than bismuth, and also of tin which is slightly paramagnetic. To this end it was proposed to measure the minute gravitational attraction between each of the above masses and a very much smaller nearby mass of some metal, the same small attracted mass to be used in all cases. In such a scheme the large masses would do nearly all the attracting, and their several gravitational pulls per unit of mass would be comparable.
To carry out this scheme Professor Dayton C. Miller very kindly provided, from his large collection of physical apparatus, a beautiful instrument designed for class-room demonstration of gravitational attraction between two small silver balls and two large lead spheres in the usual manner of such apparatus. It is a modification of the apparatus designed and used by Professor C. V. Boys for determining the gravitation constant and the mean density of the earth. Each small silver ball weighs three fourths of a gramme, and the pair are mounted at the ends of a horizontal small straight metal rod, with their centers 3.6 cm. apart. Rising from the center of this connecting rod is a small vertical rod carrying, at a distance of 6 cm. above the silver balls, the usual small mirror for scale reading, set at an angle of 45° with the ball-carrying rod. These parts constitute the oscillating system, and are suspended by a long quartz filament in a brass tube, the balls only projecting below the tube into a narrow glass-walled chamber, made shallow in order to minimize convection currents inside. Means are provided for leveling the whole apparatus, for orienting the free-hanging system and for. clamping the balls when not in use. The apparatus is permanently grounded through one of its leveling screws.
The large lead spheres and their carriages were discarded and replaced by a light reversible wooden carriage.
The photograph, Plate V., shows the apparatus as set up in my basement laboratory. The delicate part first described is mounted on a heavy marble slab firmly bracketed in the angle of two twenty-inch brick walls. These are inside walls, and hence not liable to sudden