thus constituted the structure of an atomic electric charge can be directly specified, so far at any rate as is required for a knowledge of its interaction with other electric charges at sensible distance, whereas the absence of any conception of what constitutes electrification had previously been commonly regarded as the fundamental obstacle to the electrical development of aether-theory. The order of ideas thus indicated, when carried through up to its logical extent, involves the explanation of the atomic character of matter itself: matter must be constituted of isolated portions each of which is of necessity a permanent nucleus or singularity in and belonging to the aether, of some such type as is represented for example by a minute vortex ring in perfect fluid or a centre of permanent strain in a rotationally elastic medium. It is thus natural to infer that the ultimate atom of electricity is one aspect of the entity which constitutes the ultimate atom of matter, a conclusion which (foreshadowed as above in set terms by Davy) is almost demonstrated by Faraday's electro-chemical law expressing an exact numerical connexion between them. The question must of course remain open as to whether other forms of activity besides this electrical one can be recognized in the constitution of the atom of matter: as yet nothing seems to have been found in the ascertained types of general physical and chemical phenomena which demands a further amplification, so that any advance in that direction would at present be premature if not gratuitous. For it is to be borne in mind that the proper aim of an atomic theory is not to attempt the impossible task of reducing once for all the whole complex of physical activity to rule, but is rather to improve and connect accepted methods of explanation of the various main regular types of interaction that have been brought to light in this field of knowledge. It is incumbent on us to recognize an aethereal substratum to matter, in so far as this proves conducive to simplicity and logical consistency in our scheme of physical relations, and helpful towards the discovery of hitherto
