318 Mr. T. J. Bowlker on the Factors serving 
between my theory and experimental facts in the electro- 
dynamics of the relative uniform motion of electric and 
magnetic masses, the Lorentz theory finds unsurmountable 
difficulties on theoretical grounds. As was first conclusively 
shown by Abraham, the Lorentz deformation excludes a 
purely electromagnetic basis of mechanics. The work of 
the external electric forces acting on the electron does not 
have its exact equivalent in the increase of the electro- 
magnetic energy of the electron. Therefore a certain inner 
energy of non-electromagnetic character must be ascribed to 
.the electron. The same conclusion must be drawn from 
Mr. Cunningham's calculations, if they are properly interpreted. 
Mr. Cunningham says the Lorentz-Einstein theory is the 
only theory that can account for certain optical phenomena. 
In fact, he asserts that it is required " to explain how a 
light-wave travelling outwards in all directions with velocity 
C relative to an observer A may at the same time be travelling- 
outwards in all directions with the same velocity relative to 
an observer B moving relative to A with velocity r." 
Mr. Cunningham then proceeds to show that this require- 
ment is satisfied by the Lorentz-Einstein transformation. 
I am not aware that such a " requirement " is necessary to 
explain any known fact of observation. 
XXXI. On tlte Factors serving to determine the Direction of 
Sound. By T. J. Bowlker *. 
IX the summer of 1906, while on a steamship off the coast 
of Maine, U.S.A., I was roused about midnight by the 
blowing of foghorns, and presently followed the shock and 
grinding of a collision. It appeared to me that the accident 
could only be explained by a mistake in judging of* the 
direction of the foghorns of the colliding vessels. This accident 
suggested a study of the factors determining the direction 
from which sound appears to come. 
During the winter of 1906-1907 I made some experi- 
ments. In one of them I placed the ends of two rubber tubes 
of equal lengths at the ears and moved the end of one towards 
or away from the source of sound. With equal lengths of 
tube I thought that the friction and resonance effects would 
be the same. The sound, as heard through the tubes, did 
appear to move somewhat to one side or other of the 
head, but the movements did not appear to have any relation 
to the wave-length, and the movements were very irregular. 
* Communicated by the Autkcr. 
