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Physics. — “Considerations on Gravitation)’. By Prof. H. A. LORENTZ. 
§ 1. After all we have learned in the last twenty or thirty years 
about the mechanism of electric and magnetic phenomena, it is natural 
to examine in how far it is possible to account for the force of gra- 
vitation by ascribing it to a certain state of the aether. A theory 
of universal attraction, founded on such an assumption, would take 
the simplest form if new hypotheses about the aether could be avoided, 
i.e. if the two states which exist in an electric and a magnetic field, 
and whose mutual connection is expressed by the well known elec- 
tromagnetic equations were found sufficient for the purpose. 
If further it be taken for granted that only electrically charged 
particles or ions, are directly acted on by the aether, one is led to 
the idea that every particle of ponderable matter might consist of 
two ions with equal opposite charges — or at least might contain 
two such ions — and that gravitation might be the result of the 
forces experienced by these ions. Now that so many phenomena 
have been explained by a theory of ions, this idea seems to be more 
admissible than it was ever before. 
As to the electromagnetic disturbances in the aether which migh 
possibly be the cause of gravitation, they must at all events be of 
such a nature, that they are capable of penetrating all ponderable 
bodies without appreciably diminishing in intensity. Now, electric 
vibrations of extremely small wave-length possess this property; hence 
the question arises what action there would be between two ions 
if the aether were traversed in all directions by trains of electric 
waves of small wave-length. 
The above ideas are not new. Every physicist knows Le Saar’s 
theory in which innumerable small corpuscula are supposed to move 
with great velocities, producing gravitation by their impact against 
the coarser particles of ordinary ponderable matter. I shall not 
here discuss this theory which is not in harmony with modern phy- 
sical views. But, when it had been found that a pressure against 
a body may be produced as well by trains of electric waves, by rays 
of light e.g., as by moving projectiles and when the RÖNTGEN-rays 
with their remarkable penetrating power had been discovered, it 
was natural to replace Le SaGe’s corpuscula by vibratory motions. 
Why should there not exist radiations, far more penetrating than 
even the X-rays, and which might therefore serve to account for a 
force which as far as we know, is independent of all intervening 
ponderable matter ? 
I have deemed it worth while to put this idea to the test. In 
