Notices respecting New Books. 239 



point in the same direction. The inference to be drawn from 

 Fievez's experiments alone would rather be, I think, that the 

 temperature of the flame is changed in his experiments than 

 that a specific action of magnetism on the emission and ab- 

 sorption of light exists. By experiments already in progress 

 I hope to settle the dubious points. 



Summarizing we may say : — Had the experiments of 

 Fievez come to my knowledge they would have been a motive 

 for me to further investigation, Fievez not having prosecuted 

 his inquiry up to a decisive result. At least at present it 

 remains even doubtful whether the phenomenon observed by 

 Fievez with a magnetized flame is really to be attributed to 

 the specific action of the magnetic field on the period of the 

 vibrations of light, which I have found and undoubtedly 

 proved by the experimental confirmation of Lorentz's pre- 

 dictions. 



Amsterdam, February 1897. 



XXXIII. Notices inspecting New Boohs. 



Das Wesen der EleJctrizitdt tend des Magnetismus, anf Grund fines 

 einheitlichen Siibstanzlegriffes.. By J. Gr. Yogt. Leipsic : 

 "Wiest, 1897. 

 HTHE author of this treatise is obliged to borrow from the Eng- 

 -*- lish language expressions strong enough to characterize the 

 ordinarily accepted notions concerning the aether and matter, 

 which he designates as "absurd" and "stupid." His philosophic 

 mind refuses, much more emphatically than that of a certain 

 eminent British statesman, to admit the existence of an aether and 

 of atoms in a state of perpetual vibration. He sees no difficulty, 

 however, in filling space with a continuous, contractile aether, 

 containing nuclei which undergo periodic fluctuations of density ; 

 matter consists of the permanently condensed portions of this 

 aether. We are not told how these centres of condensation differ 

 from the rest of the aether, or by what process they pull the 

 surrounding medium ; their only function is to perpetually expand 

 and contract. In fact, the theory is only the opposite extreme of 

 the kinetic theory ; every point in the aether is supposed to be the 

 seat of potential- or strain-energy instead of kinetic energy. 



The author avoids any mathematical statement of his theory, 

 sometimes by remarking that he is not a physicist, which is an 

 obvious fact, and sometimes by explaining that his work is intended 

 as a popular exposition. The volume is printed in German 

 characters, and its illustrations are so extremely bad that the 

 author finds it necessary to make an apology for them. J. L, H. 



