The magnificent researches of Andrews on the Isothermals of Carbonic Acid formed, as it were, a nucleus in a supersaturated solution, round which an immediate crystallization started, and has since been rapidly increasing.

At this, the concluding meeting of the Session, some observations and information are expected from, the Chairman for the night, and which I now, at the request of the Council, proceed to offer.

The instruments which we have called chromomictors, have been designed for the purpose of mixing lights of different colours for experiments in physiological optics. There are already a considerable number of instruments for this purpose, but none of them are perfectly satisfactory. We shall here describe one or two new forms of apparatus which have been recently experimented with, and though they may not be suitable for many colour experiments, yet they seem to possess some advantages over several of the instruments now in use.

1. It is well known that if hn denote the sum of the homogeneous products of a, b, c, … l of n dimensions, while h′n refers similarly to b, c, d, … l, then

The proof, which is very simple, may be stated thus :— We have

The island of New Caledonia, from which these ores of nickel and cobalt are derived, is situated in the South Pacific Ocean, distant about 600 miles east from Queensland, Australia. The island is about 200 miles long by about 30 miles broad, and is extremely mountainous. New Caledonia belongs to the French, and it is there that they have established one of their principal penal settlements.

In October 1881 I published in the Quarterly Journal of Mathematics (xviii. pp. 110–149) a “List of Writings on Determinants,” which contained the titles of all the books, pamphlets, memoirs, magazine articles, &c, which were then known to me to exist on the subject of the Theory of Determinants. The list consisted of 489 entries arranged in chronological order, the first date being 1693, and the last 1880. During the three years which have elapsed since it was published, I have been steadily making manuscript additions to it, not merely in the way of continuation for the purpose of keeping it up to date, but also by the intercalation of omitted titles unearthed in the course of my own researches, or brought to my notice by obliging correspondents.

In my paper on “Chemical Affinity and Solution,” read before the Royal Society of Edinburgh on 16th February last, I gave some general proofs of the correctness of my theory of solution, taken from Thomson's researches on thermo-chemistry, as given in Muir and Wilson's book on that subject. In the present paper I propose to extend these proofs, and to show the laws of solution, so far at least as chlorides, bromides, and iodides are concerned. I have verified these laws in the case of many sulphates, and have no doubt they govern all cases of solution. My theory is simply this, “Solution is due to the chemical affinities of the constituent atoms or elements of the body dissolved for the constituent atoms of the solvent.” For instance, the solubility of BaCl2 in water is due mainly to the affinity of the Ba of the salt for the O of the water, and of the Cl of the salt for the H of the water, and the degree of solubility depends on the relation between these affinities.

A very important inquiry—suggested by Mr Chamberlain when President of the Board of Trade—has just been concluded by the Trinity House of London into the relative merits of electricity, gas, and oil, as lighthouse illuminants, on which I think it advisable to make a few remarks, as the general results of the investigation ought to possess a certain amount of interest for this Society.

The object of the following experiments, which were suggested by Professor Chrystal, was to determine the relative values of the intensity of the horizontal component of magnetic force, due to a current flowing in the coils of the Helmholtz galvanometer, for different parts of its field.

After seeing in the course of one of Sir W. Thomson's lectures an experiment showing the contraction which takes place when a solution of common salt is mixed with water, I resolved upon making a number of experiments with a view to noting the result of mixing various solutions.

The paper which I have the honour of presenting to you to-night is similar in construction to those I have previously brought under your notice on the For and Madi Tribes.

The Waganda are very different from the tribes further north, and a description of them will I think aptly illustrate the very marked contrasts presented by the various Central African Tribes.

This paper is the outcome of 12 months' private spectroscope building, two months' observing therewith, and ten months' computing and graphical presenting of the observations. The result is a Solar Spectrum map, extending through so many as 60 double quarto plates, but capable of being arranged for the cheapest photolithographic reproduction, in a manner very easy to examine, convenient for reference, and yet at the same time affording at every point new and severe tests for its degree of accuracy.

It may be within the recollection of the Fellows of the Society, that in December 1883 I had the honour of reading, in this room, a paper on the Madi Tribe of Central Africa.

The mature Ovum of Myxine.—The earliest description of the mature ovum is that given by Allen Thomson, in the article “Ovum” in Todd's Cyclopædia of Anatomy and Physiology, vol. v., published in the year 1859. He says:—“I have found that in the Myxine glutinosa the globular yolk is enclosed in a horny capsule of similar consistence and structure (to that of Elasmobranchs), but of a simple elongated ellipsoidal shape; and in place of four terminal angular tubes there are a number of trumpet-shaped tubular processes projecting from the middle of the two ends, which probably serve the same purpose as the differently shaped appendages of the ova of the shark and skate.” He gives a figure in woodcut of the ovum, and of one of the threads magnified. The figures are correct with this exception: in the representation of the entire ovum the yolk is represented in outline as though seen through the envelope, and is globular, like the yolk of Elasmobranchs. In the Myxine ovum the yolk fills the cavity of the ellipsoidal envelope. It is not true that the terminal processes are tubular. I have examined them, and found them solid, and, as far as can be seen with a low power, homogeneous. I have not been able to ascertain from what specimen or specimens the description of Thomson is taken, but there is a single specimen of the ripe ovum in Professor Turner's museum which may have been examined by Thomson. This specimen was brought to the museum in the time of Professor Goodsir, but it is not possible now to ascertain whether it was dredged from the sea-bottom or taken from a pregnant female.

The following paper is an account of a preliminary experiment performed in the Edinburgh University Physical Laboratory, with the view of determining the thermal conductivity of ice.