THE ETHER AND MOVING MATTER 115 



in the two systems, the electrons must have different masses depend- 

 ing on whether their vibrations are parallel or perpendicular to the 

 velocity of translation. This startling conclusion of Lorentz is borne 

 out by what we now know of the dependence of the effective mass 

 of an electron upon what is taking place in the ether. Such an hypo- 

 thesis as this would require that Michelson and Morley's experiment 

 should always give a negative result. 



Of electrical experiments on the drift of the ether we have one 

 second order test carried out very recently by Trouton at the sugges- 

 tion of the late Professor Fitzgerald. The latter, reasoning on the con- 

 dition of a magnetic field produced by a charged condenser moving 

 edgewise to the drift of the ether, and the consequent additional 

 supply of energy of such a system on charging, thought that this 

 might produce a mechanical drag on charging and an opposite impulse 

 on discharging, just as might occur if the mass of earth were to 

 become suddenly greater. This experiment was carried out in the 

 form of a condenser mounted upon an arm carried by a delicate sus- 

 pension, with negative results. A second and more sensitive test 

 was made later in a modified form by Trouton and Noble. Since, 

 edge on to the drift, we have a magnetic field, while at right angles 

 it vanishes, the energy will vary with the azimuth, and we shall have 

 a maximum in an azimuth of 45. A delicate suspension carrying 

 the armature of a condenser showed no movement, although the 

 calculated effect was ten times the limit of observation. The negative 

 results of these experiments may be accounted for on like assump- 

 tions with that of the Michelson and Morley experiment, namely 

 a contraction or change in the dimensions of the condenser pro- 

 ducing corresponding changes in density and potential difference of 

 the charge. 



The assumption of a contraction suggests at once, from what we 

 know of transparent media, the anisotropic state which such media 

 are thrown into under dimensional strain. Rayleigh has examined 

 this question in the case of water, carbon disulphide, and glass with- 

 out result. In the case of glass his sensibility was several times the 

 calculated second order effect, and much more in case of liquids. 



The degree of refinement to which the polariscopic test lends 

 itself is perhaps beyond that of any other instance in physical appli- 

 cation. Here then is an opportunity to examine the question beyond 

 what theory has anticipated, and the test has been carried so as to 

 reach safely a third order effect, with negative results. The experi- 

 ments as performed by the writer consisted in sending a beam of 

 sunlight plane polarized at 45 to the horizon, through 28.56 meters 

 of water in a horizontal direction and examining the same by a sen- 

 sitive elliptic analyzer. On rotating the entire system from the me- 

 ridian, where the one component of vibration to the drift was parallel 



