, generate around
themselves a transverse electromagnetic wave which is propagated with
the velocity of light; for the charged particle becomes, as soon as it
experiences a change of speed, the centre of a radiation. Thus is
explained the phenomenon of the emission of radiations. In the same
way, the movement of electrons may be excited or modified by the
electrical forces which exist in any pencil of light they receive, and
this pencil may yield up to them a part of the energy it is carrying.
This is the phenomenon of absorption.

Professor Lorentz has not contented himself with thus explaining all
the mechanism of the phenomena of emission and absorption. He has
endeavoured to rediscover, by starting with the fundamental
hypothesis, the quantitative laws discovered by thermodynamics. He
succeeds in showing that, agreeably to the law of Kirchhoff, the
relation between the emitting and the absorbing power must be
independent of the special properties of the body under observation,
and he thus again meets with the laws of Planck and of Wien:
unfortunately the calculation can only be made in the case of great
wave-lengths, and grave difficulties exist. Thus it cannot be very
clearly explained why, by heating a body, the radiation is displaced
towards the side of the short wave-lengths, or, if you will, why a
body becomes luminous from the moment its temperature has reached a
sufficiently high degree. On the other hand, by calculating the energy
of the vibrating particles we are again led to attribute to these
particles the same constitution as that of the electrons.

It is in the same way possible, as Professor Lorentz has shown, to
give a very satisfactory explanation of the thermo-electric phenomena
by supposing that the number of liberated electrons which exist in a
given metal at a given temperature has a determined value varying with
each metal, and is, in the case of each body, a function of the
temperature. The formula obtained, which is based on these hypotheses,
agrees completely with the classic results of Clausius and of Lord
Kelvin. Finally, if we recollect that the phenomena of electric and
calorific conductivity are perfectly interpreted by the hypothesis of
electrons, it will no longer be possible to contest the importance of
a theory which allows us to group together in one synthesis so many
facts of such diverse origins.

If we study the conditions under which a wave excited by an electron's
variation