340 



SCIENCE. 



[Vol. XXII. No. 568 



rent of energy, in the form of kinetic energy. Temperature is 

 heat potential, and specific heat is heat capacity. It is 

 evident, therefore, that, like the gi-amme, the calorie 

 must vanish from a rational system of units, and its 

 place be taken by the erg and joule. Unit heat flux is 

 one erg per second. Unit difference of heat potential is 

 one degree C. (Theoretically, it should be the tempera- 

 ture to vfhich one erg will raise unit mass of unit matter, 

 i. e., unit mass of hydrogen.) 



Unit specific heat will be possessed hj a body which 

 requires one erg to raise one cubic c. m. one degree C. 



The consideration of the gravitational formulte gives us 

 some ideas in regard to gravity, and suggests some ex- 

 periments which have as yet not been tried. The resist- 

 ance of mass to motion, or inertia, varies directly as the 

 acceleration, and as the mass. It is independent of place 

 or the actual distance passed over in attaining the 

 velocity. The energj' possessed by a body in motion is 

 proportioned to the integral of the various accelerations 

 received by it, squared; i. e., it varies as the velocity 

 squared. 



We have an exact analogy to this in the case of motion 

 of matter in a frictionless fluid. Suppose a ball placed in 

 a fluid, such as water, which we will suppose to be fric- 

 tionless. Then, on moving the ball, we may conceive of 

 a vacuum being formed behind the ball, and that this 

 vacuum will be proportional to the square of the velocity 

 with which we move the ball through the water. The 

 water is, of course, supposed to have inertia, otherwise 

 the vacuum would not form. So long as the velocity 

 wi h which the ball is moving is constant, no work is 

 done, and there is, therefore, no resistance to the motion, 

 and it will continue in motion forever, unless opposed by 

 some force. Suppose, however, that the ball meets with 

 an obstacle which tends to stop it, then the vacuum will _ 

 tend to close up, and the water will push the ball ahead, 

 till an amount of work has thus been done equal to that 

 done in making the vacuum originally. Such a behavior 

 corresponds exactly with the behavior of matter moving 

 in the ether. 



This theory, however, demands a reconception of the 

 ether, for it is generally taken that the ether possesses no 

 inertia. On closer examination, however, it will be seen 

 that the difference is only apparent. In all the cases 

 where we have had opportunity for measuring any inertia 

 of the ether, a finite quantity only of the ether has been 

 in motion. In the case of an electric circuit, for instance, 

 the only ether in motion is that definite amount corres- 

 ponding to the current produced. It is, of course, well 

 known at the present time that electrical energy is not 

 transmitted along the wire, but through the dielectric, 

 but this does not affect the statement made that the only 

 inertia effect which could be perceived would be that due 

 to the motion of a definite amount of ether. Therefore, 

 as no inertia effect has ever been found in connection with 

 the motion of the ether in an electric circuit, we are jus- 

 tified in saying that the inertia of the ether is negligable 

 in such a case. But we are not justified in saying that 

 the inertia is negligable in the case where an infinite 

 amount of ether is in motion, as would be the case, 

 according to this theory, when a solid is moved through 

 space, for an infinite amount of the infinitely small may 

 be appreciable. 



If, however, we take the two fluid theory of electricity, 

 which, as Dr. Lodge has shown, is forced upon us by the 

 consideration of many phenomena, and consider an elec- 

 tric current as the shearing past each other of two dis- 

 similar parts, which together make up the ether, then 

 there need be no such modification of our views, for, 

 since in any case of electric flow there are always equal 

 quantities of plus and minus electricity, and we may sup- 



pose the moments of inertia equal and opposite, no inertia 

 effect could, of course, ever be observed in an electric 

 circuit. When, however, the ether is moving as a whole, 

 the inertia effects would be added instead of subtracted, 

 and we would have, as shown above, all the phenomena 

 of gravitational inertia. 



It is, of course, not necessary for a body to have mass 

 in order to display inertia effects, for its resistance to 

 motion may be due to a "counter-motive" force, as in a 

 circuit having self-induction; consequently there is no 

 difficulty in accounting, in various ways, for the ether 

 showing an inertia eft'ect. 



To take up the theory, for it is more than a mere 

 imagining, having been worked out mathematically 

 with some fullness in several directions; from 

 Fizeau's experiment (confirmed by Michaelson aad oth- 

 ers), we know that when matter moves it drags with 

 it a certain amount of the ether, but that a certain 

 part remains behind, flowing through the matter. If this 

 ether has any inertia (using the word in its broad 

 sense), then there will be an efilect similar to that which 

 occurs when a sieve is moved through water. A 

 vacuum, or a spot of less density, or of less rigidity 

 will be formed behind the body. The size of this spot 

 will vary as the velocity, and if the velocity is doubled 

 the spot will be doubled, and four times as much work 

 will be done in making it. And this no matter what the 

 time in which the spot (which we will call the vacuum, 

 provisionally) is formed, or where in space it is formed. 

 On taking away the driving force the ether will close tip 

 on the body again, and push it on, till the vacuum exists 

 no longer, and consequently all the work done in form- 

 ing it is given up again. As the ether is supposed to 

 have no friction, mere motion of the vacuum from one spot 

 in space to another will nece-isitate no work and conse- 

 quently we have Newton's law, that a body fends to con- 

 tinue in its state, whether of moving with a given velocity, 

 or at rest. 



This is the part of the theory which deals with inertia, 

 and the experiment referred to above is as follows : Set 

 a body in motion, under the action of a constant force, 

 then remove the force, and examine the body at the time 

 when the force is removed. It' the ether has inertia, then 

 at the instant when the accelerating force is removed 

 there will be an abnormal reduction in speed for an ex- 

 ceedingly small time. This will be followed hj an abnor- 

 mal acceleration, also acting for a very small time, and 

 of such dimensions that after the lapse of a very small time, 

 the velocity of the body will be the same as if neither the 

 retardation nor the acceleration had existed. If the time 

 during which these effects take place be not too small, it 

 will be observable on a chronograph, and will give a trace 

 as follows : 



The dotted line shows the trace if the effect had not 

 taken place, the other the trace if the effect does occur. 

 It will be seen that they only differ for an exceedingly 

 small portion of time, and it is doubtful if the ex23eriment 

 would succeed, even if the effect existed. It has, how- 

 ever, I believe, never been looked for. 



If this be the true theory of inertia, then the theory of 

 gravitation is as follows: If we take a rod of anj- solid 

 substance, and press down one atom, which we will call A, it 

 pulls down the atom next it, which we will call B, because, 

 though the atom B is moving, it merely oscillates about a 

 fixed point, and is always within reach of the influence of 

 A. This property is what we call rigidity, and it is this 

 which enables a solid to stand a shearing stress. 



