During the cruise of the Challenger the specific gravity of the surface water was observed daily while at sea, and that of water from the bottom and intermediate depths as often as opportunity offered. These observations were almost entirely confined to the region between the parallels of 40° N. and 40° S. latitudes, which, including as it does the regions of the equatorial calms, of the trade winds, and to a certain extent of both the northern and southern westerly winds is decidedly the most interesting field for such investigations. Many valuable observations have been made by other observers, and I have availed myself more especially of the series of observations made by Lenz during Kotzebue's voyage to the Pacific and back. His observations were almost entirely confined to the surface water.

The manganese nodules occur in greater or less quantity all over the ocean-bed, and most abundantly in the Pacific. They occur of all sizes, from minute grains to masses of a pound weight, and even greater, and form nodular concretions of concentric shells, round a nucleus, which is very frequently a piece of pumice or a shark's tooth. Their outside has a peculiar and very characteristic mammillated surface, which enables them to be identified at a glance. When freshly brought up they are very soft, being easily scraped to powder with a knife. They gradually get harder on exposure to the air.

In drawing the various closed curves which have a given number of double points, I found it desirable to have some simple mode of ascertaining whether a particular form was a new one, or only a deformation of one of those I had already obtained. Of course the schemes (as described in my former paper) contain the desired information, but it may sometimes be difficult to obtain in this way; for, when the number of intersections is large, we may have to change the crossing which is taken as the initial one several times before we hit upon the same notation for like crossings (if such exist) in the two schemes compared. And the methods of deformation already given often present their results in forms so distorted that it is not easy at once to recognise their identity with other drawings of the very same curves.

Several years ago Professor Dewar gave me a specimen of silica in a state of exceedingly minute division, which had been produced in Dr Playfair's laboratory in the preparation of fluosilicic acid. I noticed at the time how much its great mobility is increased by heating—so that it behaves almost like a liquid. And I fancied that I observed close to the surface a thin stratum of what might by the same analogy be called a vapour; consisting of particles thrown up and falling back again, like the little drops thrown up at the surface of soda-water. I was inclined to ascribe these phenomena to heat directly—supposing that the particles were fine enough to behave, though in a very imperfect way, as the kinetic theory assumes the particles of a gas to behave.

Mr Milne Home stated that he had been induced to resume his researches in the Lochaber district, in consequence of a lecture, in June last, by Dr Tyndall of London, at the Royal Institution, Albemarle Street, and subsequently printed and published. In this lecture, Dr Tyndall controverted the detrital theory of lake barriers, and advocated the glacier theory;—supporting his views by a reference to observations which Dr Tyndall said he had recently made on a special visit to the Parallel Roads.

When a polished thin straight wire turns on a fixed point in space, the point at which light coming from a fixed source is reflected, moves in a curved surface. In this paper the motion of the wire was supposed to be restricted to the plane passing through the eye and the source of light. The curve was shown to be of the third order, having a straight line as a symptote both ways, and to depend for its form upon a characterising angle. The interest of the subject lay chiefly in the remarkable transformations of the curve.

The following is but a short and incomplete account of a compound formed on the carbon and binding screws of a makeshift Leclanché battery. The cells employed were ordinary Bunsen elements, of which the carbon was embedded in manganese dioxide; the substance in question grew on the brass binding screws, and as a thin layer on the carbon. The external appearance of the mass was reniform, the colour ranging from a pale blue to a dark purple and lilac tint; the portions from the carbon were of a pale green shade, and of no special shape. The quantity being small, it was impossible to make more than one analysis of each substance and that only with very small quantities.

In a work recently published by Professor Plantamour on the climate of Geneva, the hourly means of the aqueous vapour of the atmosphere for each month is given, deduced from observations made during the twenty-seven years ending with 1875. The curves drawn from these figures are undoubtedly the most remarkable of the meteorological specialties of the climate of Geneva.

At the last meeting of the Society I stated that I had just procured a remarkable essay by Listing, part of which bears on the subject of knots, and that I had found in it an example of a change of form not producible by the modes of deformation I had employed.

It had for some time struck me as very singular that, thoug I could easily prove that (when nugatory intersections are removed) a knot in which the crossings are alternately over and under is not farther reducible, I could not prove all its possible deformations to be producible by inversions or projections of the kinds specified in my paper; but, as soon as I recognised the existence of amphicheiral forms, I saw that it was probable that they would furnish a key to my difficulty. I immediately set to work to classify the simpler of such forms; and while I was thus engaged I got the Göttinger Studien for 1847, in which is Listing's paper, with the title Vorstudien zur Topologie.

The investigation, of which this paper contains the first part, was undertaken with the view of throwing light on the constitution of salts of trimethl-sulphine.

These salts have been represented in two different ways—1st, as compound of tetratomic sulphur, and 2d, as molecular combinations of sulphide of methyl with methylic ethers, just as the ammonia salts have been represented as compounds of pentad nitrogen, or as molecular combinations of ammonia with hydric salts.

Though in my former papers on knots I have made but little allusion to cases in which two or more closed curves are linked together, the method I have employed is easily and directly applicable to them. I stated to the British Association that the number of intersections passed through in going continuously along a curve, from any intersection to the same again, is always even—whether it be linked with other curves or not Hence, even when a number of closed curves are linked together, the intersections may be so arranged as to be alternately over and under along each of the curves.

The general result of these strictly preliminary experiments appears to show that for sparks not exceeding a decimetre in length (L), taken in air at different pressures (P), between two metal balls of 7mm·5 radius, the requisite potential (V), is expressed by the formula

The Holtz machine employed is a double one, made by Ruhmkorff, and it was used with its small Leyden jars attached. The measurements had to be made with a divided-ring electrometer, so that two insulated balls, at a considerable distance from one another, were connected, one with the machine, the other with the electrometer.

These experiments, so far as they go, confirm the results formerly obtained by Mr Durham, Proc. VII. 788.

The method employed was the same as that described (Proc. VIII. 623), but the high conducting power of gas coke for electricity made the experimental work very difficult. The results, so far, are not very consistent with one another, but they appear to point to a diminution of conductivity by rise of temperature.

The note had reference to some sensational statements recently made under the the title “Are we drying up.” But it led also to a curious hydrostatical question as to the equilibrium arrangement of water poured into a shaft already full of air, and supposed to be so deep that in its lower parts the air is compressed to a density exceeding that of water. This suggested numerous questions, such as: What addition to the atmosphere would raise the sea from the earth's surface?

Notwithstanding the fact that substances supposed to affect the flow of the bile have been administered to man for more than 2000 years, there is still very great uncertainty as to what does and what does not augment the biliary excretion. The indefinite state of knowledge regarding this point is due to the circumstance that variations in the flow of bile from the human liver are estimated by simply observing the colour of the dejections,—a method that is of necessity exceedingly rough, for it is impossible thus to detect slight variations in the excretion of bile, especially when, as in the case of rhubarb, the substance gives to the dejections a colour similar to that of the bile, and where, as in the case of sodium sulphate, the substance gives rise to copious dejections of a watery character, whereby the colour is diluted.

The specimen was found near Wanlockhead, Dumfriesshire, in 1872, by Andrew Gemmell, miner, who unfortunately broke up the piece, and disposed of the fragments to different parties in the locality. Mr Dudgeon was enabled to get possession of all the fragments, and has restored the mass to its original form. The specimen is a very interesting one, being the largest known piece of auriferous quartz found in Scotland; and Mr Dudgeon thought it would interest the fellows of the Society to exhibit it at the meeting before placing it in the Museum of Science and Art, which has now been done with the consent of the different owners.