43« POPULAR SCIENCE MONTHLY 



It is a question before all of endeavoring to obtain a more satis- 

 factory theory of the electrodynamics of bodies in motion. It is there 

 especially, as I have sufficiently shown above, that difficulties accumu- 

 late. It is useless to heap up hypotheses, we can not satisfy all the 

 principles at once; so far, one has succeeded in safeguarding some 

 only on condition of sacrificing the others; but all hope of obtaining 

 better results is not yet lost. Let us take, then, the theory of Lorentz, 

 turn it in all senses, modify it little by little, and perhaps everything 

 will arrange itself. 



Thus in place of supposing that bodies in motion undergo a 

 contraction in the sense of the motion, and that this contraction is the 

 same whatever be the nature of these bodies and the forces to which 

 they are otherwise subjected, could we not make a more simple and 

 natural hypothesis? We might imagine, for example, that it is the 

 ether which is modified when it is in relative motion in reference to 

 the material medium which penetrates it, that, when it is thus modi- 

 fied, it no longer transmits perturbations with the same velocity in 

 every direction. It might transmit more rapidly those which are 

 propagated parallel to the motion of the medium, whether in the same 

 sense or in the opposite sense, and less rapidly those which are propa- 

 gated perpendicularly. The wave surfaces would no longer be spheres, 

 but ellipsoids, and we could dispense with that extraordinary contrac- 

 tion of all bodies. 



I cite this only as an example, since the modifications that might 

 be essayed would be evidently susceptible of infinite variation. 



Aberration and Astronomy. — It is possible also that astronomy 

 may some day furnish us data on this point; she it was in the main 

 who raised the question in making us acquainted with the phenomenon 

 of the aberration of light. If we make crudely the theory of aberra- 

 tion, we reach a very curious result. The apparent positions of the 

 stars differ from their real positions because of the earth's motion, and 

 as this motion is variable, these apparent positions vary. The real 

 position we can not ascertain, but we can observe 1?he variations of the 

 apparent position. The observations of the aberration show us, there- 

 fore, not the earth's motion, but the variations of this motion; they 

 can not, therefore, give us information about the absolute motion of 

 the earth. 



At least this is true in first approximation, but the case would be 

 no longer the same if we could appreciate the thousandths of a second. 

 Then it would be seen that the amplitude of the oscillation depends 

 not alone on the variation of the motion, a variation which is well 

 known, since it is the motion of our globe on its elliptic orbit, but on 

 the mean value of this motion, so that the constant of aberration would 

 not be quite the same for all the stars, and the differences would 

 tell us the absolute motion of the earth in space. 



