A

is that a temporary star results from the collision of a dark body with a nebula, the chances of such a collision being much greater than the collision of two dark bodies. necessary consequence will be an intense superficial heating with an atmospheric expansion in all directions. In whatever direction an observer may be situated, spectroscopic observations will show, (1) a displacement violet-wards of absorption lines or bands due to the absorptive action of the expanding and cooling atmosphere advancing in the direction of the observer with the hotter interior parts of the star as background; and (2) bright bands due to the expanding atmosphere to right and left of the body of the star, there being in this case no brighter background and no spectral shift. Dr. Halm now imagines that the collision is due to the advance of the dark body into a stream of nebulous matter passing obliquely across the dark body's path. This will at once give rise to a circulation of parts of the nebula round the star, and these, of course, will also be highly heated. The portions moving transverse to the line of sight across the face of the star will produce absorption bands in their normal position in the spectrum, while the marginal portions moving on the one side towards the observer and on the other side from him will produce a shift of bright bands both towards the red and towards the violet end of the spectrum. By compounding the effects of these two conditions, namely, the simple expansion of the atmosphere equally in all directions and the swirl of incandescent matter due to oblique collision, Dr. Halm showed that the two types of spectra obtained in the cases of the recent Novæ were at once obtained.-Three papers by Dr. Thomas Muir were also communicated, the titles being "The Sum of the Signed Primary Minors of a Determinant," "Continuants Resolved into Linear Factors," and "The Three-line Determinants of a Six-by-Three Array."

November 21.-Lord M'Laren in the chair.-Mr. George Romanes, C.E., read a paper on a possible explanation of the formation of the moon. The general idea was that the moon had grown to its present form and size by the gradual agglomeration of what was originally a ring of satellites broadly similar to what we know to exist in the case of Saturn. On this hypothesis it was easily shown that the process of agglomeration of a comparatively small body like the moon could not be accompanied with an evolution of heat sufficient to produce a molten globe, and that in consequence the ordinary assumption of intense volcanic action to explain the so-called craters was difficult to accept. But at seemed possible to account for the rugged mountainous surface of the moon with the "seas," ridges, craters,' and peaks by means of the bombardment of those meteoric masses, large and small, which in virtue of the combined action of moon, earth, and sun were precipitated from time to time upon the lunar surface. In the absence of an atmosphere the masses so precipitated would impinge upon the surface with high enough velocities to render the material in the immediate vicinity liquid, the impinging mass also itself being liquefied wholly or partially according to circumstances. The author entered into a detailed examination of some of the most striking features of the moon's surface, and showed how this hypothesis accounted for them. He also exhibited a mass of lead into which small bullets had been shot at various incidences. The indentations reproduced the leading characteristics of the lunar craters, even to the small hill in the middle of the main depression. It was also noticed that at the instant of impact the rim of lead thrown up all round was made red hot. The mysterious streaks so characteristic of Tycho in certain aspects were explained as due to great splashes of material hich settled down in thin crystalline layers capable of throwing off the reflected sunlight in definite directions.Prof. Coker described a laboratory apparatus for measuring the lateral strains in tension and compression members. By a well designed combination of levers and mirror attachment an apparatus capable of being fixed to the bar itself had been constructed, which was sufficiently rigid and yet sensitive enough to measure a change of 1/20,000th of an inch. Some experiments on steel, iron, and brass bars were described, in which the new apparatus was used in conjunction with Ewing's extensometer, and values of Poisson's ratio were given to three significant figures. The talues varied from one-third to one-fourth.

PARIS.

Academy of Sciences, November 28.-M. Mascart in the chair. On the possibility of chemical reactions: M. de Forcrand. The author contends that the rigid application of the thermodynamical condition of the possibility of a chemical reaction is neither practical nor necessary, and that the empirical rule that the disengagement of heat settles the course of a reaction is the only possible experimental criterion of the possibility of chemical reactions.On the prediction of chemical reactions: M. de Forcrand. In general, accurate prediction of the course of a chemical reaction is impossible, but there are two rules or principles, one rigorous the other approximate. The latter, the principle of maximum work, is a simplification of the first, and ought to be considered as the only practical guide.-M. Dastre was elected a member in the section of medicine and surgery in the place of the late M. Marey.-The Leonids in 1904 Lucien Libert. Details of observations made at Havre on the nights of November 14, 15, and 15, 16. III meteors were observed and the trajectories measured.-On the singularities of uniform analytical functions: D. Pompeiu.-On a new class of ions: G. Moureau. In

a previous paper it has been shown that a saline vapour becomes conducting after passing through a porcelain tube heated to about 1000° C., and remains conducting at much lower temperatures, possessing the properties of an ionised gas. In the present paper the mobilities of these new ions have been measured. It was found that in the neighbourhood of the region of ionisation the mobilities of the vapours are of the same order as the ions of the gases issuing from a flame. On the genesis of temporary radio-activity: Ed. Sarasin, Th. Tommasina, and F. J. Micheli. The authors conclude from the results of their work that a very close relation appears to exist between ionisation and the production of temporary radio-activity. The two phenomena would appear to be reversible, the production of the temporary radio-activity of a body being due to the absorption, or, perhaps, adsorption of an emanation which is formed during the ionisation of a gas. On this view, the radio-activity would consist in the loss by radiation of the emanation adhering to radio-active bodies, this causing, in its turn, the ionisation of a gas.-Stereoscopy without a stereoscope: A. Berthier. The author points out that he has already published a description of a method similar in principle to that given by M. Ives in the Comptes rendus of October 24 last.-On the colloidal state of matter: G. E. Malfitano. The author regards colloidal matter as a system formed of an electrolyte dissociated into ions and insoluble molecules grouped round these ions.-The influence exerted by the removal of the moisture from the air supplied to the blast furnace: A. Lodin. The results obtained by Gailey at the Isabella blast furnaces, near Pittsburg, on he effect of drying the air forced into the furnace, have attracted much attention in Europe, not unmixed with scepticism. The author makes a comparison of the heat balances in the two cases, and shows where the economy is effected. One indirect effect of the drying process is to increase the temperature of the ingoing air, and a considerable portion of the economy effected may be attributed to this cause. In Europe, where it is usual to work with the air entering the tuyeres at a much higher temperature than at the Isabella furnaces, the relative economy which would be produced by drying the air would be too small to justify the capital expenditure required to introduce the necessary plant. On the use of dry air in blast furnaces: Henri Le Chatelier. The economy claimed for the use of dry air is ascribed by the inventor of the process to the fact that the moisture of the undried air transforms a certain proportion of the coke into hydrogen and oxide of carbon. From the figures of the amount of water removed it is possible to calculate exactly this loss; it is 5 per cent., or only one-fourth of the amount claimed. It is certain, then, either that the economy claimed is incorrect, or else that the true cause is to be sought for elsewhere. The author shows that the quality of the iron produced, especially as regards its sulphur impurity, is an important factor, and that when the sulphur is to be kept down to a certain percentage the economy of fuel claimed by Gailey may be real. -On wood spirit from Thuya articulata, Algeria: Emilien Grimal. Carvacrol, thymohydroquinone, and thymoquinone were isolated from the product of the distillation

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