M. Benoist has founded on the transparency of matter to the rays a
sure and practical method of allowing them to be distinguished, and
has thus been enabled to define a specific character analogous to the
colour of the rays of light. It is probable also that the different
rays do not transport individually the same quantity of energy. We
have not yet obtained on this point precise results, but it is roughly
known, since the experiments of MM. Rutherford and M'Clung, what
quantity of energy corresponds to a pencil of X rays. These physicists
have found that this quantity would be, on an average, five hundred
times larger than that brought by an analogous pencil of solar light
to the surface of the earth. What is the nature of this energy? The
question does not appear to have been yet solved.
It certainly appears, according to Professors Haga and Wind and to
Professor Sommerfeld, that with the X rays curious experiments of
diffraction may be produced. Dr Barkla has shown also that they can
manifest true polarization. The secondary rays emitted by a metallic
surface when struck by X rays vary, in fact, in intensity when the
position of the plane of incidence round the primary pencil is
changed.
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