Page:The Annual Register 1899.djvu/531

 1899.] SCIENCE. 107

has disclosed the possession of remarkable energies. Its peculiar radi- ations persist undiminished after an imprisonment for three years in a wooden box encased with lead, and in a mine 2,800 feet beneath the surface its behaviour is unchanged. Since its reflected rays produce a greater photographic effect than those that are direct, it must be •capable of setting up secondary radiations in other bodies. A disc of an inactive substance placed immediately over a radio-active sub- stance acquires the property of emitting Becquerel rays and of rendering air conductive of electricity.

Sir W. Crookes thinks that uranium may have the faculty of ap- propriating from the rapidly moving, as distinct from the slowly moving, molecules of air an energy that it expends in maintaining a radiation across the ether; and that the necessary smallness and shortness of such waves make them comparable to the rays of Rontgen.

The fact that electrical conductivity is produced by uranium ra- diation is explained by Mr. Rutherford on a theory of ionisation. He finds, also, that uranium emits two kinds of rays, of which the one is more penetrative, less easily absorbed by gases, has more photographic power, and passes a hundred times more freely through aluminium than the other kind. They are both unaffected by the impact of kathodic rays.

M. and Mme. Sklodowska-Curie have extracted from pitch blende some sulphide which they believe to be that of a new metal, polonium, and which is 400 times as active as uranium. To Sohncke's rule, that 4he fluorescence of all bi-refracting crystals is polarised, the salts of uranium are an exception. Herr Schmidt finds that uranyl compounds of sodium and potassium acetates effect no polarisation.

A corpuscular view of Rontgen rays is taken by Herr Walter. They are not intermittent pulses, but are discharged kathodic particles much smaller than electro-chemical ions, and they possess a highly penetrative power by virtue of the very fact that they carry no charge. Herr Geitler, indeed, believes them to be incapable of carrying a charge. Lord Kelvin, having observed that kathodic rays which strike the antikathode normally are more efficient in producing Rontgen rays than those which strike it obliquely, considers that the Rontgen rays are actually due to the electric charges, carried by the kathodic par- ticles, being imparted to the antikathode.

Professor Sutherland prefers the view that electricity exists in separate natural units, the electrons, which are not always associated with atoms to form ions. If a positive and a negative electron unite to form a neutron it is insulated by the ether until it is exposed to an external force sufficient to decompose it, and then the ether acts as a conductive electrolyte. The ions that he believes to be undoubtedly present in the kathodic stream are quite subordinate to the stream of electrons ; and when they impinge upon an aluminium window the ions are arrested and the electrons get through as Lenard rays. Lenard rays and kathodic rays both carry negative electricity, both originate Rontgen rays, both colour haloid salts, both have magnetic and electric deflectibility, and both can excite luminescence. The colouring of salts would be by the electrons attaching themselves to electro-negative