It is now some years since the late Sir William Crookes attempted to explain the periodicity of the properties of the elements on the theory that they have all been evolved by a conglomerating process from some primal stuff--the protyle--consisting of very small particles. He represented the action of this generative cause by means of a “figure of eight” spiral, along which the elements are placed at regular intervals, so that similar elements come underneath one another, as in Mendeléeff’s table, though the grouping differs in some respects. The slope of the curve is supposed to represent the decline of some factor (_e.g._, temperature) conditioning the process, which process is assumed to be of a recurrent nature, like the swing of a pendulum. After the completion of one swing (to keep to the illustration of a pendulum) whereby one series of elements is produced, owing to the decline of the above-mentioned factor, the same series of elements is not again the result as would otherwise be the case, but a somewhat different series is produced, each member of which resembles the corresponding member of the former series. Thus, if the first series contains, for example, helium, lithium, carbon, &c., the second series will contain instead, argon, potassium, titanium, &c. The whole theory, though highly interesting, is, however, by no means free from defects. The Corpuscular Theory of Matter. § =79.= We must now turn our attention to those recent views of the constitution of matter which originated to a great extent in the investigations of the passage of electricity through gases at very low pressures. It will be possible, however, on the present occasion, to give only the very briefest account of the subject; but a fuller treatment is rendered unnecessary by the fact that these and allied investigations and the theories to which they have given rise have been fully treated in several well-known works, by various authorities on the subject, which have appeared during the last few years.[95] [95] We have found Prof. Harry Jones’ _The Electrical Nature of Matter and Radioactivity_ (1906), Mr. Soddy’s _Radioactivity_ (1904), and Mr. Whetham’s _The Recent Development of Physical Science_ (1909) particularly interesting. Mention, of course, should also be made of the standard works of Prof. Sir J. J. Thomson and Prof. Rutherford.