From the results obtained by Berzelius in his experiments with tungsten, the number 189·28 is calculated as the atomic weight of that metal. Many later investigations have been made, in which uniformly a lower figure was arrived at, in the majority of cases very nearly 184, which has therefore been regarded as the atomic weight.

The immense amount that has been written on the subject of dew renders it extremely difficult for one to state anything regarding it which has not been previously expressed in some form. It has been examined over and over by minds of every type, and from every point of view; so that every possible explanation of the different phenomena seems to have been given, and so many passing thoughts recorded, that from the literary point of view the whole subject seems exhausted. As a necessary result, these different treatises are in many respects contradictory; and it would be quite impossible to construct anything like a consistent explanation and account of our subject, from the very voluminous writings of those who have treated it from the purely literary point of view, and whose ideas have been evolved from their inner consciousness, according to what seemed to them the fitness of things, and without questioning nature as to the truth of their conclusions. On the scientific side of the subject, however, the writings are not so voluminous, and additions to it are still required to enable us to determine which of the many conflicting opinions are correct.

The attempt to account for the behaviour of gases by attributing their apparently continuous pressure to exceedingly numerous, but nearly infinitesimal, impacts on the containing vessel is probably very old. It certainly occurs, with some little development, in Hooke's tract of 1676, Lectures de potentiâ restitutivâ, or of Spring; and, somewhat more fully developed, in the Hydrodynamica of D. Bernoulli, 1738. Traces of it are to be found in the writings of Le Sage and Prévost some 80 or 90 years ago. It was recalled to notice in 1847 by Herapath in his Mathematical Physics, and applied, in 1848, by Joule to the calculation of the average speed of the particles in a mass of hydrogen at various temperatures. Joule expressly states that his results are independent of the number of the particles, and of their directions of motion, as also of their mutual collisions.

The purpose of this memoir is (1) to make known a number of drawings and descriptions of the eggs, embryos, and larvæ of the species of Teleosteans which I have been able to study at the Scottish Marine Station; (2) to review as comprehensively as possible what is known at the present time concerning the structure of the embryos and larvæ of the species of Teleosteans, and to discover what features are common to each family or each order; (3) to discuss the changes which take place in the protoplasm and nucleus of the mature ovum immediately after it is shed, both when fertilised and when unfertilised. The ova of the following species were taken directly from the parent fish, and artificially fertilised. The necessary operations were carried out, in some cases by myself, on board fishing boats—usually steam trawlers from Granton. In many instances I did not myself go out in the boats, but the ova were obtained and brought to me at the laboratory by Alexander Turbyne, keeper of the station. But in every case there is no uncertainty as to the species of the fish from which the ova were taken; if there was any doubt, specimens of the parent fish were brought with the ova.

In a Review of Dr Stur's Zur Morphologie und Systematik der Culmund Carbonfarne, I pointed out that he appears to have included two types of fern fructifications in his genus Calymmatotheca.

The first type includes those forms originally placed in Calymmatotheca and consists of a number of exannulate sporangia arranged around a common point of attachment; the second type, which was first described in Zur. Morph., u. Syst. d. Culm- u. Carbonfarne, is there represented by C. Avoldensis and C. Frenzli. The fruit of these two species is apparently surrounded by an involucre or indusium, and it is only with this part of the fructification that we are at present acquainted. I also further indicated that in Calymmatotheca, as I proposed to restrict the genus, the fruiting portions of the frond are entirely deprived of foliage pinnules, whereas in the other type (C. Avoldensis and C. Frenzli) only a very slight modification takes place in the fertile portion of the fronds—the sporangia being borne on the ordinary foliage pinnules.

The first impression upon the mind of the reader of the above title will probably be, that the subject has long since been exhausted. The explanation of these colours, as due to interference, was one of the first triumphs of the wave-theory of light; and what Young left undone was completed by Poisson, Fresnel, Arago, and Stokes. And yet it would be hardly an exaggeration to say that the colours of thin plates have never been explained at all. The theory set forth so completely in our treatises tells us indeed how the composition of the light reflected depends upon the thickness of the plate, but what will be its colour cannot, in most cases, be foretold without information of an entirely different kind, dealing with the chromatic relations of the spectral colours themselves.

In the following paper I desire to place on record the results of certain experiments which have lately engaged my attention. The facts established are, so far as I am aware, novel and in themselves interesting.

Many of the physical properties of hydrogenised palladium or hydrogenium have been carefully studied by Graham, Dewar, and others; but no one seems to have called attention to its thermoelectric peculiarities, or to have made a special study of its electrical resistance. These two inquiries form the subject of this paper. Throughout I shall use, for brevity's sake, the name Hydrogenium, which was applied by Graham to the fully-saturated form.

In the Proceedings of the Royal Society of Edinburgh for 1874–75 there is a short paper on the “Electrical Resistance of Iron at a High Temperature.” It is the record of certain experiments made by three of us, then students in the Physical Laboratory of the University of Edinburgh; and its conclusion is that there is a peculiarity in the behaviour of iron as an electric conductor at the temperature of a dull red heat. At this temperature other physical peculiarities are known to exist, particularly as regards its thermal expansion, its thermal capacity, and its specific heat for electricity. The discovery of these striking properties we owe respectively to Dr Gore, Professor Barrett, and Professor Tait.

A little more than a year ago, I was led to conclude that the primitive hypoblast in pelagic Teleostean ova was derived mainly from the unsegmented protoplasm forming the floor of the segmentation cavity. In this respect my results were mainly in harmony with the researches of Lereboullet (21), Kupffer (18 and 19), Klein (16), Van Bambeke (3), and others, but opposed to the more recent investigations of Henneguy (10), Hoffmann (14), Kingsley and Conn. (15), Ryder (24), Agassiz and Whitman (1), and Cunningham (8.) At that time I adopted Agassiz and Whitman's name of periblast for the subgerminal layer containing free nuclei, though I differed from those authors in my idea of the mode of origin of the nuclei. As, however, I regard the tissues derived from this layer as belonging chiefly to the parablastic group of His and Waldeyer, I propose to return for the present to the older name of parablast. I was not enabled to trace the origin of this layer in my earlier investigations, and thus failed to grasp its significance. More recently I have had an opportunity of studying the development of several other types, particularly the herring and cod. In the herring the germinal mound is not formed until after fertilisation. Partly owing to this circumstance, and partly also to the early period at which the assimilation of yolk commences, the eggs of the herring are particularly well suited for a study of the parablast question.

The sponge Suberites domuncula attracted the attention of the Italian naturalist Olivi almost a hundred years ago, but was on account of its firm india-rubber like consistency erroneously regarded as an Alcyonium. Beyond the general diagnosis of Nardo who erected the genus Suberites, the structure of the sponge has, I believe, remained virtually unknown. Not for this reason, however, but because the Monaxonia in general, of which Suberites is an example, are still for the most part but little known, Prof. F. E. Schulze of Berlin was good enough to ask me last winter to investigate the structure of this sponge. To him, therefore—perhaps the greatest living authority on the subject—I may be allowed to express my gratitude for the hospitable reception with which he welcomed a stranger to his laboratory, and for the constant interest and assistance with which he encouraged my work. That I have not succeeded in giving a perfect elucidation of the structure is largely due to the same cause which has kept it for so long almost wholly unknown. The crowded siliceous spicules, the compact consistence, the smallness of the ciliated chambers, make the histological analysis somewhat difficult. Such gaps as exist in my investigation I hope to be able to fill up by the study of related forms, and have with that end begun the study of Suberites mana.

During a short visit I paid to Oxford in the month of June last I had the opportunity of examining, by the kind permission of Professor Moseley, a number of specimens of Bdellostoma Forsteri, which were some of a large number brought from the Cape by Mr Adam Sedgwick of Trinity College, Cambridge. This examination showed what, from the close affinity of the two forms, was naturally to be expected, namely, that the structure of the reproductive system and the development of the reproductive elements in Bdellostoma were very closely similar to the structure and development of the corresponding parts in Myxine. A short time ago I described before the Society some ovarian eggs of Myxine, obtained at the beginning of the present year, which were approaching maturity. In these eggs there were slight projections at the poles, and on the surface of the projecting parts a number of papillæ. The projections were caused by the growth of a number of threads from the vitelline membrane within the ovarian capsule, and the papillæ were the separate elevations produced by the threads.