SECTION VII.

Volcanic Showers or Rain.

1. General Remarks.

THE enormous violence with which, during eruptions, the mate. rials that compose the bowels of the volcano are ejected into the atmosphere, and the disturbance which is usually communicated to the aerial regions, produce a conjoint force which is frequently sufficient to drive such materials in the course of the wind to a distance of several hundred miles; and the finer particles or dust to that of several hundred leagues. We proceed to give a few examples. [Editor.

2. Shower of Ashes in the Archipelago.

By Capt. William Badily.

December 6, 1631, riding at anchor in the Gulf of Volo, about ten o'clock that night, it began to rain sand or ashes, and continued till two o'clock the next morning. It was about two inches thick on the deck, so that we threw it overboard with shovels, as we did snow the day before. The quantity of a bushel we brought home, and presented to several friends, especially to the masters of the Trinity House. There was no wind stirring when these ashes fell; and they not only fell in the places where we were, but likewise in other parts, as ships were coming from St. John d'Acre to our port; though at that time a hundred leagues from us. We com. pared the ashes together, and found them both alike.

3. Shower of Dust that fell on a Ship between Shetland and Iceland: in a Letter from Dr. Robert Whytt, Prof. Med.

By letters from a passenger on board a ship bound from Leith for Charlestown in South Carolina, it appears that on the night of the 23d or 24th of October last, when the weather was quite calm, a shower of dust fell on the decks, tops and sails of the ship, so that next morning they were covered thick with it. The ship at this time was between Shetland and Iceland, about twenty-five

leagues distant from the former, and which was the nearest land. This shower was probably owing to the great eruption, which happened at mount Hecla in Iceland, in October.

4. On a new kind of Rain. By the Count de Gioeni, an inhabi. tant of the third Region of Mount Etna. Translated from the Italian.

The morning of the 24th inst. (April 1781) exhibited here a most singular phenomenon. Every place exposed to the air was found wet with a coloured cretaceous grey water, which, after evaporating and filtrating away, left every place covered with it to the height of two or three lines; and all the iron-work that was touched by it became rusty. The shower extended from N. & N.E. to S. S. W. over the fields, about seventy miles in a right line from the vertex of Etna. There is nothing new in volcanos having thrown up sand, and also stones, by the violent expansive force generated within them, which sand has been carried by the wind to distant regions. But the colour and subtilty of the matter occasioned doubts concerning its origin; which increased from the remarkable circumstance of the water in which it came incorporated; for which reasons some other principle or origin was sus pected.

It became therefore necessary by all means to ascertain the na. ture of this matter, in order to be convinced of its origin, and of the effects it might produce. This could not be done without the help of a chemical analysis. To do this then with certainty, I endeavoured to collect this rain from places where it was most probable no heterogeneous matter would be mixed with it. I therefore chose the plant called Brassica Capitata, which having large and turned up leaves, they contained enough of this coloured water; many of these I emptied into a vessel, and left the contents to settle till the water became clear. This being separated into another vessel, I tried it with vegetable alkaline liquors and mineral acids; but could observe no decomposition by either. I then evaporated the water, to reunite the substances that might be in solution: and touching it again with the aforesaid liquors, it showed a slight effervescence with the acids. When tried with the syrup of violets, this became a pale green; so that I was persuaded it contained a

calcareous salt. With the decoction of galls no precipitation was produced. The matter being afterwards dried in the shade, it appeared a very subtile, fine earth, of a cretaceous colour, but inert, from having been diluted by the rain.

I next thought of calcining it with a slow fire, and it assumed the colour of a brick. A portion of this being put into a crucible, I applied to it a stronger heat, by which it lost almost all its acquired colour. Again, I exposed a portion of this for a longer time to a very violent heat, from which a vitrification might be expected; it remained however quite soft, and was easily bruised, but returned to its original dusky colour. From the most accurate observations of the smoke from the three calcinations, I could not discover either colour or smell that indicated any arsenical or sulphureous mixture. Having therefore calcined this matter in three portions, with three different degrees of fire, I presented a good magnet to each; it did not act either on the first or second; a slight attraction was visible in many places on the third; this persuaded me, that this earth contains a martial principle in a metallic form, and not in a vitriolic substance.

The nature of these substances then being discovered, their volcanic origin appears; for iron, the more it is exposed to violent calcination, the more it is divided, by the loss of its phlogistic prin. ciple; which cannot naturally happen but in the great chimney of a volcano. Calcareous salt, being a marine salt combined with a calcareous substance by means of violent heat, cannot be otherwise composed than in a volcano. As to their dreaded effects on ani. mals and vegetables, every one knows the advantageous use, in medicine, both of the one and the other, and this in the same form as they are thus prepared in the great laboratory of nature. Vegetables, even in flower, do not appear in the least macerated, which has formerly happened from only showers of sand.

How this volcanic production came to be mixed with water may be conceived in various ways. Etna, about its middle regions, is generally surrounded with clouds that do not always rise above its summit, which is 2900 paces above the level of the sea. This matter being thrown out, and descending on the clouds below it, may happen to mix and fall in rain with them in the usual way. It may also be conjectured, that the thick smoke which which the

volcanic matter contained might, by its rarefaction, be carried in the atmosphere by the winds, over that tract of country; and then, cooling so as to condense and become specifically heavier than the air, might descend in that coloured rain. I must, however, leave to philosophers, to whom the knowledge of natural agents belongs, the examination and explanation of 'such phænomena, confining myself to observation and chemical experiments.

P. S. On Friday the 4th of May, about a quarter past three in the afternoon, a slight shock of an earthquake was felt in the country about Etna, which became more sensible at some distance from the mountain; its direction was from north to south. The volcano had continued its flames and explosions; and the night before, a column of smoke, composed of globes as it were piled on each other, had ascended over the crater to double the height of the mountain, as far at least as one could judge at the distance of twentytwo miles, which the vertex is in a right line from this city. This remained the whole night perpendicular, only one of the globes had separated and lengthened out to the westward from the summit. Now and then all the inside of the column, and of the lengthened outpart, became illuminated by electric fire, which was of a deep red colour, and gradually went out again, beginning at the bottom, in about two seconds. The fire has continued on the crater till this day, May 8th, ejecting red-hot masses or stones, which rolling beautifully down the cone, have illuminated this region; some lava has run over from the crater towards the W.N.W. but without having force enough to burst the sides or walls of the volcano.

5. Surprising Shoal of Pumice-stones found floating on the Sea. By John Dove *.

On the 22d of March, 1724-5, at noon, being in the latitude of 35° 36′ south, and longitude 4° 9' west, with variation 3° 16′ W. they discovered several pumice-stones on the sea; but not expecting any such thing at that distance from the land, the islands Tristan d'Acunha being the nearest, which were judged to bear W. 9° 10′ S. distance 186 leagues, they disputed what it might be ; when about one P. M. they took up a piece in a bucket, which confirmed Mr. Dove's opinion of its being pumice-stones. Towards night it was spread all round, as far as could be seen. Next morning the pumice-stones were very thick, in drifts, lying N.N.E. and S.S.W. and extended out of sight from the mast head, increasing as they ran to the eastward.

Wednesday the 24th they continued their course E.S.E. 140 miles, the pumice-stones being thicker; so that for sixteen hours some of the drifts were about a cable's length broad, and so thick, they could scarcely see the water between them; and there was much the same breadth between the drifts, with several pumice. stones interspersed. Towards noon, they found the pumice somewhat thinner: latitude 37° 35′ S. and longitude 1° 4′ W.

Thursday the 25th, in the evening, the drifts were near as large as above, but towards next morinng they decreased much; so that about noon they were clear of the pumice-stones, several of which were as large as a man's head. They sailed 317 miles since they first discovered them. They lay just in the track for ships out. ward bound; and all the ships that went out the same year and since, who go so far to the southward, have fallen in with them, In the morning they tried the current, but found none and no ground at 130 fathoms. At noon, latitude 37° 54′ S. longitude 0° 38′ E. they judged Tristan d'Acunha bore W. 3° 39′ N. Distance 256 leagues, supposing it to lie in latitude 37° 5′ S. and lon, gitude 15° 38′ W.

[Phil. Trans. 1728.

We give this curious article a place here, as the pumice-stones must neces sarily have fallen down in showers.-EDITOR.