112 PHYSICS OF ETHER 



In fact, Fizeau himself has stated since that his observations were 

 not absolutely decisive. While the test is now probably within ex- 

 perimental limits with the more highly refined half-shade systems, 

 other modes of experimenting on different optical principles with 

 greater sensibilities have given negative results, thus disproving the 

 existence of a phenomenon which Fizeau's experiment apparently 

 established, and making a repetition of this experiment, which is of 

 doubtful execution, unnecessary. 



The effect of the motion of a natural rotative substance through 

 the ether on the rotation of the plane of polarization is of considerable 

 importance in its bearings on certain controverted points in some of 

 the recent theories of a quiescent ether. Mascart, who first studied 

 the problem in the case of quartz, was unable to detect any differ- 

 ence in the rotation when a ray was propagated in and against the 

 direction of motion of the earth. This variation in the total rotation, 

 which he could detect, was one part in 20,000, or one part in 40,000 on 

 reversal. This experiment as thus carried out corresponds to a first 

 order effect. Rayleigh quite recently has repeated this experiment 

 with a sensibility five times as great, and obtained negative results, 

 likewise. The impossibility of obtaining quartz in sufficient quantity 

 and purity, or natural rotary liquids of sufficient power, to attain the 

 extreme limit of polariscopic possibilities seems to make even an 

 approximation to a second order effect entirely improbable, although 

 the higher frequencies might be used, where the power may be ten 

 times as great. On the other hand, the effect of the mechanical 

 rotation of such a medium on the circular components is, however, 

 probably not beyond experimental possibilities in polariscopic work. 



On the electrical side several first order experiments have been 

 made which likewise have given negative results. Des Coudres has 

 attempted to determine the difference in the induction on each of 

 two coils placed symmetrically, with respect to a third coaxial coil 

 between them. On compensating for the effects of each on the galvan- 

 ometer when the axis of the system was in the direction of drift, and 

 then reversing the direction of the system, no influence on the gal- 

 vanometer could be observed. The effect which should be observed 

 corresponds to the second order of the aberration. However, without 

 compensating factors, the theory of induction phenomena shows 

 that second order effects should be looked for in systems moving 

 through the ether. The same may be said of other electrical exper- 

 iments. 



The difficulties in formulating a theory which will explain the 

 results of all experiments involving tests to the first order of sensi- 

 bility only on the assumption of either a quiescent or a convected 

 ether, are much easier met than when second and higher orders have 

 to be taken into consideration. Here we find what, at first sight, 



