THE ETHER AND MOVING MATTER 109 



(1 /i 2 )v. This hypothesis satisfies the phenomena of aberration 

 and the uniformity of the laws of reflection and refraction of a body, 

 whether in motion or at rest, and, as already mentioned, does not 

 affect interference, as Stokes showed, so far as the earth's motion is 

 concerned. That the ether apparently is carried along within moving 

 matter not with its full velocity, but diminished to the extent indi- 

 cated by Fresnel's coefficient of convection, Fizeau demonstrated 

 in his famous interference experiment with streaming water, repeated 

 later with greater refinement by Michelson and Morley. The signi- 

 ficance of this experiment in its bearings on the question of the drift 

 of the ether has perhaps been overestimated. In fact, neglecting the 

 square of the aberration, it is exactly what we should expect from 

 the dynamical reaction of a moving material system on a periodic 

 disturbance, propagated through it without reference to the motion 

 of translation of the interpenetrating medium, but simply to the fre- 

 quency of the vibration impressed upon the system by this ether. 

 Thus if we transform the ordinary differential equations of motion 

 of the material system from fixed to moving axes, the form of the 

 solution contains Fresnel's convection coefficient as a factor exactly, 

 neglecting quantities of the second order of the aberration. This 

 experiment cannot then be adduced as a positive result in favor of a 

 quiescent ether. On account of its physical consequences, however, 

 it should be extended to the case of gases and to absorbing substances, 

 using light corresponding to the natural frequences of the latter if 

 possible. Although negative results have heretofore been obtained 

 with a gas, yet, with high pressures and greater dimensions and 

 velocities, the test is within present experimental limitations. Results 

 with solid bodies are still lacking, but a preliminary examination of 

 the problem encourages us to expect successful results, at least with 

 double-refracting substances. Reasoning in a similar manner as on 

 the dynamical reaction of a moving system, we should look for the 

 acceleration of a circularly polarized ray propagated coaxially within 

 a rapidly rotating medium. This may possibly be brought within 

 experimental limits. Again we have the important experiment of 

 Lodge on the effect of moving masses upon the motion of the ether 

 near them. This experiment, like that of the preceding one of Fizeau, 

 is a first order test, i. e. the effect to be observed would arise from 

 a change in the first power of the aberration factor. Two interfering 

 beams were sent around several times in opposite directions between 

 two rotating steel disks, and the effect on the bands noted from rest 

 to motion or reversal. With a linear velocity not far from one two- 

 hundredth that of the earth's orbital motion, and a distance of 

 some ten meters or more, no influence on the interfering rays could 

 be detected, thus making the effect, calculated from the aberration 

 factor if the ether were carried around between the disks, something 



