242 REPORTS ON THE STATE OF SCIENCE. 



system. Thus, for instance, the magnetic effect of a rotating electrified 

 sphere would be observable by instruments carried round with the sphere ; 

 they would not be obscured by the fact that the recording instruments 

 shared in the rotational motion. 



Media lies and Relativity. 



In the light of the principle of relativity there are some interesting 

 aspects of the status of the old dynamics. 



If v 2 is neglected the space-time transformation of relativity reduces 

 to what was called above a Newtonian transformation. The suggestion 

 arises ; supposing relativity to be a universal hypothesis, what knowledge 

 does it give concerning molar dynamics ? Is Newtonian dynamics an 

 approximate science in which we are consistently neglecting v 2 ? Can 

 we formulate a more exact scheme conforming to the principle and reducing 

 for small molar velocities to that of Newton ? What modified meaning 

 must be attached to the words mass, momentum, kinetic energy. 



An illustration may be given of the kind of modification that will be 

 necessary. 



Let us suppose that a conventional material particle carrying a charge t 

 is at rest in an electric field. It will begin to move with an acceleration 

 which would ordinarily be determined by equations 



dX „ d*Y _ d*Z _ 



in gip = £ Ji„ m ^p — f E„ m gp — e E., 



taking (X, Y, Z, T) as the space-time system in which it is initially at 

 rest. 



Applying the transformation, the same motion is represented by the 

 equations 



dx 



m dt 



Vi - ift<>- 



\ = ic x , 



— w c- 7 



dz 



m s 



-<(*-M- 



\<s/l—- w 2 /cV 



where w is the total velocity of the particle (having components 



dx dy dz 

 dt' It' dt' 



whose instantaneous values are v, o, o). These equations contain the 

 theory of the results of the experiments of Kaufmann and Bucherer on the 

 variability of the accelerations of electrons moving with different velocities 

 in the same field. 



