Second and Ihird Order Tests oftlie " JEtlier Drift* 



13 



analysis of both Lorentz and Abraham seems to be equally 

 consistent with Kaufmann's results on the deflexion of 

 Becquerel rays, Lorentz conforms Abraham's theory to his 

 own, by shrinking the undef ormable spherical electrons of the 

 latter into flattened ellipsoids in the line of drift : while 

 Abraham himself shows that these will be unstable unless 

 the greatest axis is in this direction. The latter writer shows * 

 that work must be done against the electrical forces to produce 

 this deformation, so that the total energy in any acceleration 

 is greater than that furnished by the outside forces. 



Hence there must be inner forces as well which determine 

 the form of the electron. Thus the hypothesis of Lorentz 

 is incomplete without defining the law of forces further. 

 Hence we must either abandon the contraction hypothesis or 

 modify it. The assumption that the quasi-elastic forces, 

 which maintain the electrons in their positions of equilibrium, 

 experience the same changes as the electrical forces, may 

 possibly be varied, and, together with a modification of the 

 previous hypothesis, be adapted so as to agree with all 

 observations. 



While the negative results of the first order experiments 

 involving a study of phase relations between periodic dis- 

 turbances from the same radiant, optical or electrical, moving 

 with the system, are quite as consistent with a^mobile — if we 

 neglect second and higher orders — as with a fixed aether, the 

 explanations of the negative results of second and third 

 order tests are still not in full harmony or free from criticisms, 

 notwithstanding the bold assumption in the premises. 



It becomes then a serious question, whether to seek still for 

 decisive results with experiments involving the higher order 

 tests, on the one hand, or direct entrainment tests on the 

 other, in order to settle the question. 



The recent repetition by Morley and Miller f of the original 

 Michel son-Morley interference experiment, with a sensibility 

 one hundred times the calculated effect, leaves perhaps no 

 question as to the absence of any such second order optical 

 effect. Lorentz's analysis requires a negative result, likewise, 

 if the rays pass through a transparent substance instead of a 

 vacuum ; and it seems desirable therefore that this point 

 should be tested for water, sav. 



The interferometer method might also be used to test for 

 double refraction if the light were polarized so as to make the 

 electric displacements perpendicular to the plane of the inter- 

 fering rays, i. e. respectively parallel and perpendicular to the 



* Phys. Zeit. Band v. p. 576, 

 t Phil. Mag. Dec. 1904, p. 753. 



