The

intensely hot, and great chemical change was going on. principal crater is the most perfect and regular. It is entered from one side by a natural opening, and close to this part the floor is extremely hot, far too hot, indeed, to be touched by the hand. But the gullet, which is a cylindrical depression like a large shallow well in the centre of the bottom of the crater, about 200 feet in diameter and 20 feet deep, was closed and cold. There were three points of action in this crater, all easily recognized from some distance by the strong mirage produced by the heated air over them. Besides that on the floor of the crater close to the entrance, there were two on opposite sides, one near the bottom and the other high up. The other crater was smaller, but very much deeper and much less accessible. Its lowest point was about 150 feet below the bottom of the higher crater, and it is situated about 300 yards further from Monte Frumento. The top of this cone is only ten feet higher than the bottom of the principal crater, not including the depression formed by the gullet.

By far the most striking and characteristic feature of both these principal craters, and of the whole of the active part of the volcano generally, was the extraordinary brilliancy of the colours, almost entirely yellow, passing on one side into white, and on the other through orange into red, which defined the position of the crevices, and the places from which there was the chief issue of vapour. The great clouds of steam rising incessantly from the walls of the craters, sometimes obscured these colours; but whenever the wind drifted away the steam, they reappeared with the most startling vividness. Standing in the crater near the bottom, one could look down upon a large surface of these bright tints. On the walls of the crater, and near the top, the same thing was repeated on a large scale. Fragments of the coloured rock had fallen from time to time, and partly covered the floor, but they were much less vivid. The imagination instantly suggests that this bright yellow colour is the result of those sulphur emanations of which so much is said in the accounts of volcanic eruptions, and certainly the idea is very natural; but it is quite incorrect. Scarcely any native sulphur was to be found in these craters at the time of my visit, and none at all existed in an efflorescent state on the walls of the crater.

The history of the brilliant colours on the walls of a crater of eruption is both curious and instructive. It is, as usual in all matters concerning the structure of the earth, a history of change and metamorphosis. The vapour that issues from the interior as steam, under high pressure, and with sufficient force to eject lava or melted rock in all varieties of form and texture, brings with it various gases. At the begin

VOL. IX.-NO. IV.

T

ning and in all the early stages of the eruption, chlorine is one of the most important of these. Hydrogen, nitrogen, and oxygen are always present. Towards the close, carbonic acid gas becomes abundant. After the main crevice or fissure through which the chief eruption has come is finally closed, these gases, in various combinations, ooze through narrow cracks formed in the lava below and the erupted matter above. Thus arise the fumaroles, of which mention has been made. All these superficial rocks are porous in a very high degree; and the acid vapours at high temperature decompose the lava, depositing, either on the inside of the cells or cavities of its substance, but sometimes on the surface of the ground, many salts, some neutral, others alkaline; silica also and sulphur, are thus deposited. Within the substance of the large round blocks of cellular lava, sometimes called "volcanic bombs," ejected during the eruption, and often three or four feet in diameter, I saw, on peeling off the surface, considerable deposits of alkaline carbonate of soda. Crystals of several salts of ammonia are also common, and even common salt is met with. On the outside, where the gases emerge, the iron existing in all lava, and carried up with the gases, is deposited very readily in combination with the chlorine and hydrogen, after the first force of the eruption is over. And it is to these deposits of the salts of iron, and not to sulphur, that the intense and brilliant yellow on the face of the crater and surface of the cone are due. They are proofs that the eruptive force has diminished, and that secondary changes are taking place. The form of the deposit is curious. It is usually an incrustation, and often takes the form of small, cup-like, spongy-looking masses, white at the edges, and yellow towards the centre. It is also in groups of crystals. But very soon after it has been formed, and when the acid vapours cease, the warm vapours soon begin to produce further changes, and thus this beautiful appearance is not permanent. Exposed to the air, the iron passes into the state of peroxide; and before long, the white and yellow-coated cells of the stone lose their great beauty and brilliancy, and assume at last that deep brick-red tint familiar to every one in connection with iron rust.

Many and very interesting are the results of chemical investigation in reference to the metamorphoses produced during and subsequent to volcanic eruptions. Such events occurring at intervals, which on a large scale may be regarded as regular, alternate with much longer intervals of apparent repose, during which, however, changes are constantly going on, modifying the materials already erupted, and preparing for the next convulsive and explosive movement.

Whatever mystery may have been imagined to exist in

reference to such movements in the earth is in a fair way of being removed by the investigations of modern chemistry and physics.

Under a certain part of the earth's surface, and within certain limits of time and space, not large compared with the earth and its history, the access of sea-water to cavities existing at a moderate depth beneath the surface of the earth, produces concussive movements or earthquakes, elevations of certain tracts, and the ordinary phenomena of volcanoes. These are produced, in all probability, by very simple means, although the results seem very complicated. They may have nothing to do with any greater depth than a few scores of miles beneath the level of the sea, and they may or may not have reference to the original preparation of the earth as a habitation fit for organized beings. But being now a part of the earth's constitution, they may be studied with great advantage as an important chapter of its history, for they appear to be the chief proximate causes of those great physical features of our globe, on which all the phenomena of organization depend.

Viewed in this light, the account of a volcanic eruption, even though not one of the first magnitude, may possess great value, and the more so since there cannot be a doubt that much remains to be learnt by the chemist concerning the actual succession of events on such an occasion. The mere fact that sulphur is not always, perhaps is rarely, a common product, is one of great interest; and the additional fact that what has certainly been very often taken for sulphur is a salt of iron, and a proof that the eruption is beginning to die out, is equally important. The great volume of cloud commonly issuing from a volcanic vent certainly consists of eighty or ninety per cent. of steam; and the small proportion of muriatic acid, carbonic acid, and nitrogen sufficient to render the steam noxious has been too little attended to. Craters in eruption, and immediately afterwards, are by no means always so easy of access as in the case before us.

The condition of the lavas erupted last year from Etna is. very interesting. Among the specimens procured within the first six months from the first outburst were some illustrating every variety known. They include the most scoriaceous and the most compact, the most and the least crystalline, the most felspathic and the most basaltic, some are intensely black, some of the most delicate grey. The successive flows are stratified, and exhibit lines of vesicular and tufaceous composition between the strata. The eruption, in fact, included all the ordinary phenomena, and was not wanting in any of the incidental horrors which are too apt to mark such events. Some time after the original fissure was filled up with the cooling

lava, and the flow had stopped, a sudden and terrible earthquake took place in the immediate vicinity, by which a large proportion of the inhabitants of a village were destroyed. A yawning chasm opened beneath the village, and the miserable people were absolutely engulphed as this chasm partly closed. Some estimates were taken of the flow of the lava at the commencement of the eruption, which may be interesting and useful for future comparison.

At 200 metres from the fissure from which the lava issued, its mean velocity was estimated at ten metres per minute. This was shortly after the commencement of the eruption, and at this time it was calculated that between 5000 and 6000 cubic metres (say 12,000 to 15,000 tons) were poured out per minute. At this rate nearly eight millions of cubic metres per day would have issued, but the number of points of issue increased, and it was estimated that by the 4th of February (six days after the eruption commenced), more than 112 millions of cubic metres had been poured out (about 300,000,000 tons). The lava descended along the slopes of the mountain for about six and a half miles with unusual rapidity, averaging one and a half mile per day, but its course was fortunately checked at a very early date, and before reaching any of the villages on the mountain side, it had finished its work. It remains now visible at a great distance, and marking the event of which it is the most permanent result.

MESSINA, February 3, 1866.

MR. BROWNING'S REFLECTING TELESCOPE.

Ar the Soirée given in January by Mr. De La Rue, Mr. Browning exhibited a telescope made for Mr. Slack, which presents important new features, and was much admired. Mr. Browning also read a paper at the Astronomical Society in January, on a new mode of mounting silvered glass mirrors of moderate dimensions, and a new method of suspending the small reflector, or prism, whichever might be employed.

We now lay before our readers a sketch of the telescope made for Mr. Slack. It is furnished with a beautifully-worked mirror of rather less than 6-inches diameter, made by Mr. With, who has been singularly successful in this difficult and delicate branch of optical art. The way in which the mirror is