We cannot flatter ourselves that we have done more during our three-and-a-half years’ work than contribute a few facts towards the data necessary for the solution of the problem, “What is the cause of the beautiful phenomenon of stratification produced by electric discharges in vacuum tubes ?” which, having been first noticed by M. Abria in 1843, was independently re-observed by Mr. (now Sir William) Grove in 1852, and has since engaged the attention of so many physicists. Our excellent and highly esteemed friend the late Mr. Gassiot, working at first with an induction coil, but more recently on the same lines as ourselves (voltaic batteries of high potential), has published results of great interest, many of which are confirmed by our own experience; while, on the other hand, we have enjoyed pleasurable intercourse and exchange of thought with our contemporary, Mr. W. Spottiswoode, who is still pursuing with great acumen and originality a similar investigation, both with the induction coil and the Holtz machine, with which he has recently used condensers of great capacity, like those we employ and have described in Part I. If we arrive at the same results by different paths, the one investigation will support the other, and for each may be claimed more reliance than if unconfirmed. Throughout our labours we have felt so strongly the necessity of obtaining numerical results as data for the foundation of a theory, that we have not hesitated to risk much in this cause. By the fusion of terminals, or the sudden discharge of the condenser, we have lost a vast number of very beautiful tubes; but gradually, by the adoption of various devices, and by the employment of instruments specially constructed and insulated to suit the high potentials we deal with, we have succeeded in overcoming the various impediments, so that we can now readily obtain values for the physical quantities that enter into consideration in our experiments.

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ALTHOUGH there are several voltaic batteries which possess the esseptial quality of continuous action, yet when a very large number of elements is required, it is found that they are all in some respects inconvenient. For example, it is very troublesome to charge a battery of several hundred elements, in which two liquids and a porous cell are required; moreover, diffusion of the two liquids eventually takes place, and produces a great amount of local action whenever the battery is left for a long time with the electrodes disconnected. We believe, therefore, that the instrument which we herein describe will be foiind useful t o the chemist and the physicist as a ready source of dynamic electricity always a t hand, and that, especially where from a few hundreds to several thousand elements are requisite, it will be found t o be valuable, handy, and compact. In its construction no porous cell is needed, and the electrolyte is solid and very nearly insoluble, so that practically the electro-positive metal is scarcely attacked, even when the elements are left immersed with the electrodes disconnected for several weeks. We may state that this iristrurnent was designed for the express * A few of the values for f-a were reduced to differences in temperature, the calculations being founded upon the ahsolute determinations of the tension of acetate, in series I. ; the results, which I give only as rough approximations, were us follows. The temperatures of equal vapour-tensions are respectively :