over Jupiter, at 6h. 54m. through the middle of Orion; and at 7h. 16m. it was already in Canis Major.

There it divided itself at once into four little clouds, and losing some of its intensity of colour, disappeared by degrees, and at 7h. 40m. was quite gone. A few seconds after, the little clouds it had formed reappeared, and in less time than it takes to describe it they were seen to reunite, and to dart in all directions, jets of white light like a firework. The rays on the west and east alone remained some time, and at 8h. 12m. others appeared in number not less than ten, all which, arranging themselves on the northern side, formed as it were, a luminous fan, with its centre at B. of Orion. This novel arc, like a zenithal aurora, lasted only twenty minutes and then, gradually decreasing in size, was only entirely extinguished at about 11h. It was during this phase of our aurora that the colours of the northern zone lost some of their intensity. The meteorological state of the atmosphere presented nothing particular during the whole time of the phenomenon. There was a very light N.E. wind below, and a S.W. high up; the temperature relatively high, and barometrical pressure always increasing. We add, in the last place, that three falling stars were seen; one at 7h. 10m. from Vega to the near horizon, another at 8h. 25m. in the direction of Jupiter to the Pleiades; and the last at 8h. Jupiter towards the west.

THEORY OF HEAT.

30m. from

By J. CLERK MAXWELL, M.A. Longmans, 1871. 3s. 6d.

If the substance had been one of those which expand in melting, the effect of pressure would be to solidify some of the mixture, and to raise the temperature of fusion. Most of the substances of which the crust of the earth is composed expand in the act of melting. Hence, their melting points will rise under great pressure. If the earth were throughout in a state of fusion, when the external parts began to solidify, they would sink in the molten mass, and, when they had sunk to a great depth, they would remain solid under the enormous pressure, even at a temperature greatly above the point of fusion of the same rock at the surface. It does not follow, therefore, that in the interior of the earth the matter is in a liquid state, even if the temperature is far above that of the fusion of rocks in ore furnaces.

It has been shown by Sir W. Thomson that if the earth, as a whole, were not more rigid than a ball of glass of equal size, the attraction of the moon and sun would pull it out of shape, and raise tides on the surface, so that the solid earth would rise and fall as the sea does, only not quite so much. It is true that this motion would be so smooth and regular that we should not be able to perceive it in a direct way; but its effect would be to diminish the apparent rise of the tides of the ocean, so as to make them much smaller than they actually are.

It appears, therefore, from what we know of the tides of the ocean, that the earth, as a whole, is more rigid than glass, and, therefore, that no very large portion of its interior can be liquid. The effect of pressure on the melting point of bodies enables us to reconcile this conclusion with the observed increase of temperature as we descend in the earth's crust, and the deductions as to the interior temperature founded on this fact by the aid of the theory of the conduction of heat. pp. 20, 21.

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At the Friday evening meeting on March 22, 1872, Mr. J. N. Lockyer, F.R.S., delivered a lecture on the eclipse of December 12, 1871, to a crowded audience. He commenced by saying that his business was to state the results of the Eclipse Expedition, but as such results were embodied in the large pile of MS. on the table before him, he must necessarily confine himself to the observations made by himself and Sig. Respighi. He first pointed out on a map the course of the eclipse shadow, and the stations occupied by the various observing parties. Col. Tennant, Capt. Herschel, Dr. Janssen, Mr. Pogson and others having previously selected their stations, Mr. Lockyer chose Bekul, and Professor Respighi Poodocottah, both on the mainland, other detachments of the expedition being left in Ceylon, at Jaffna and Trincomalee. Only one party out of five into which the observers were divided, failed to see the eclipse. The lecturer then described the extent of our knowledge before the last eclipse, and stated that at the preceding one in December, 1870, the hydrogen lines of the corona spectrum had been seen by Professor Young extending to a distance of 8' from the solar disc, and 1474 Kirchhoff to a distance of 20' by the American observers in Spain. Mr. Watson's drawings in 1870, and the reversal of the Fraunhofer lines observed by Professor Young and Mr. Pye were also noticed, and Mr. Brothers' photograph taken in Sicily

VOL. X.

exhibited, which showed a most extensive corona, the rifts of which corresponded in position with the photographs taken in Spain. The great point left to be determined, therefore, was whether this extensive atmosphere of hydrogen and the unknown substance giving the 1474 line was reflected light or not.

The various instruments taken out by the expedition were exhibited and described, and a number of experiments performed with Mr. Spottiswoode's polarising apparatus and the electric lamp, to show the mode of using the biquartz and savart polariscopes, which were but partially successful. Illustrations of Professor Respighi's mode of observation were next given, in which it was very well shown that the usual form of the spectrum depended on a slit being used, and that with a crooked slit the form would be zig-zag, and with a ring aperture circles of colours would be produced, according to the nature of the elementary bodies rendered incandescent. Respighi now uses a prism in front of the object-glass of his telescope with neither slit nor collimator, and thus when the sun is covered by the moon, the constituents of the corona become visible as coloured rings. Mr. Lockyer's principal results were obtained by observing the eclipse through a powerful train of prisms, without any telescope at all, and he deduces from them that the structure of the corona appears to be that of cool prominences, and consists mainly of hydrogen and the matter of 1474 Kirchhoff. Professor Respighi, who was about 100 miles distant from Mr. Lockyer, saw in his instrument when the ordinary solar spectrum disappeared, a vivid red zone or ring and two green ones, the brightest of these latter being due to 1474 Kirchhoff, with vivid coloured jets where prominences occurred. Mr. Lockyer, using the instrument above referred to, saw the same rings with the addition of a violet one, being another of the hydrogen colours. The absence of the yellow, which is due to another element of the prominences, and which was seen when they and the chromosphere were observed, shows conclusively that the coronal light is not that of the sun or chromosphere reflected, but that for eight or ten minutes at least there is a true solar appendage or envelope, consisting of hydrogen and the unknown substance of the corona and the aurora. Mr. Lockyer then exhibited on the screen the five photographs taken by Mr. Davis at Bekul, and others obtained at Jaffna

Meeting of the Royal Astronomical Society.

III

and Ottocamund, as well as drawings by Mr. Holiday and Captain Tupman. The eye drawings showed a much greater extent of corona than any of the photographs, and the structure was evidently radiated in these more distant regions. Mr. Lockyer reserved his opinion as to the reason of this extensive appearance, and seemed to have a lingering affection for a cause not exclusively solar in this outer part of the visible corona, which he hoped would be further examined in future eclipses. In conclusion, he spoke most highly of the assistance rendered to the Expedition by the late Lord Mayo, the local officials, the Peninsular and Oriental Company, the admiral on the station, and others, and expressed his deep regret at the sad catastrophe to the GovernorGeneral which had happened since the observing party left India.

ROYAL ASTRONOMICAL SOCIETY.

Session 1871-72.

Sixth Meeting, April 12th, 1872.

Professor Arthur Cayley, F.R.S., President, in the Chair. Secretaries-E. Dunkin, Esq., and R. A. Proctor, Esq. The minutes of the last meeting were read and confirmed. Seventy-one presents were announced and the thanks of the Society given to the respective donors. It was also mentioned that Colonel Babbage had presented a large photograph of his deceased father, and that Sir John Herschel had left 50 copies of his Cape Observations to the Society, in order that every person who received the Gold Medal or other Certificate of Merit might have a copy presented to him at the same time.

G. M. Whipple, Esq.,

H. Pratt, Esq., and

H. C. Levander, Esq.,

were balloted for, and duly elected Fellows of the Society. The following papers were announced and partly read :— Observations of Encke's Comet: by Mr. Hind.

The places given extended from October 8 to December 6. The observations were made at Twickenham, some by Mr. Hind, and others by Mr. Plummer.

On the Orbit of the Binary Star & Bootis: by Mr. Hind.

The elements of this orbit were first computed by Sir J. Herschel, and afterwards by Madler. The author sent another set of elements,