and Stoke s- P lanclc s JEther. 163 



later on. In order to reduce the slip to ^ per cent, of v n a 

 condensation of about 60000 would be required *. 



In view of this considerable condensation, required by the 

 theory of Stokes-Planck, Lorentz made in 1909 (' Theory of 

 Electrons/ pp. 173-4) the following characteristic remark: — 



u In this department of physics, in which we can make 

 no progress without some hypothesis that looks somewhat 

 startling at first sight, we must be careful not rashly to 

 reject a new idea, and in making his suggestion Planck has 

 certainty done a good thing. Yet I dare say that this 

 assumption of an enormously condensed ether, combined, as 

 it must be, ivith the hypothesis that the velocity of light is not in 

 ■the least altered by it, is not very satisfactory." [The last 

 words are italicised for our present purpose,] 



In fact, such a condensation, introduced ad hoc and serving 

 only the negative purpose of not upsetting the theory of 

 aberration, did not seem very satisfactory, and the present 

 writer has as recently as 1914 expressed the same opinion 

 in his book on Relativity (p. 63), not so much to defend 

 Fresnel's and Lorentz's fixed aether, as to prepare the reader's 

 mind for the complete abolition of the aether and thus to 

 introduce him to Einstein's "special" relativity of 1905. 

 Such has been the position of things until recently. 



3. Now, it so happens that, stimulated by the desire to 

 test Einstein's generalized relativity and theory of gravitation, 

 the astronomers participating in the last Eclipse Expedition 

 have found an undoubtedly positive effect, the bending of 

 rays passing near the Sun. As I have pointed out on 

 previous occasions, it seems premature to interpret this result 

 -as a verification of Einstein's theory, not merely in view 

 of the small outstanding discrepancies, but chiefly in view of 

 the failure of detecting the spectrum shift predicted by the 

 theory, with which the whole theory stands or falls. But 

 the Eclipse result proves at any rate that there is an 

 ''alteration,''' a change of light-velocity all around the Sun, 

 which thus invalidates the words <>f Lorentz italicized in the 

 quotation above. The condensation claimed by Planck's 

 modification of Stokes's theory, for the Sun as well as for the 

 Earth and for all other material bodies, is no longer devoid 

 ■of influence on observable phenomena. It suddenly acquires 

 physical life, so to speak. 



* Notice tliat the aberration is a first order effect, while such 

 phenomena as that expected by Michelson-Morley are second order 

 effects (v' 2 /c 2 ), so that the above condensation suiting the aberration up 

 to 1 per cent, will reduce the Michelson-Morley effect to one ten- 

 thousandth of its value, and thus practically annihilate it. There is thus 

 no need for making- o- larger than 10 - 2. 



M2 



