F. On the relation between variation of electromotive force and resulting current through imperfect contacts.
G. On the systematic study of the contact-sensitiveness exhibited by metals, non-metals and metalloids.
H. On the contact-sensitiveness exhibited by alloys and compounds.
I intend to treat the above subjects in some detail, and in the present paper will especially deal with the first five lines of investigation. These, it is hoped, will afford an explanation of some of the most perplexing anomalies. All the subjects mentioned above are more or less interdependent, but their treatment in one paper would make the subject very complicated. It would be easier to take a more generalised and complete view of the subject as a whole, after each of the above-mentioned inquiries has been separately considered. With reference to the flow of electricity through imperfect contacts, I need only mention here that the phenomenon seldom obeys Ohm's law. There are in fact two characteristically different types, in the first of which the current is disproportionally increased under increased electromotive force; in the second we are presented with the astonishing result that the current is actually diminished under increasing electromotive force.
Mass Action and Molecular Action
Of the various attempts made to explain the action of contact-sensitiveness, Professor Lodge's theory of coherence has been the most suggestive. The coalescence of water and mercury drops in Lord Rayleigh's experi-
