the burning mountains, is certainly the effect of sublimation; and those great quantities of it said to be found about the skirts of the volcanos, is only an argument of the long duration and vehemency of those fires. And though sulphur vivum, or rough brimstone, as they call it, had from Hecla and Italy, is opaque, and agrees not with the transparent and amber-like sulphur vivum of the ancients, yet it does not follow, that that also was not produced by sublimation, any more than that the stalactites, or water-wrought stone, is not so made, because some of it is found opaque, and some crystalline.

But possibly the pyrites of the volcanos may be more sulphureous than ours: and indeed it is plain that some of ours in England are very lean, and hold but little sulphur, others again a great deal. And this may be one reason why England is so little troubled with earthquakes; and Italy, and almost all round the Mediterranean sea, so very much. Another reason is the paucity of pyrites in England; besides the subterraneous cavities in England are small and few, compared to the vast vaults in those parts of the world; which is evident from the sudden appearance of whole mountains and islands.

Second, on the Spontaneous Firing of the Pyrites.-It may be ob jected, that no body is kindled by itself: but it seems to be apparently otherwise; for vegetables will heat and take fire of themselves, as in the frequent instance of wet hay; and animals are naturally on fire, and men also sufficiently evince it, when in a fever; and among minerals, the pyrites, both in gross and in vapour, is actually fired of its own accord; and damps naturally take fire of themselves. Also the volcanos all the world over, argue as much; for it is very probable that they are mountains consisting in great part of pyrites, as appears by the quantities of sulphur thence sublimed, and the application of the loadstone to the ejected cinders.

Third, concerning Thunder and Lightning being from the Pyrites. -There are two sorts of instances, besides the arguments before urged, which very much favour the opinion 1 lately offered, that thunder and lightning owe their matter to the sole breath of the pyrites and although I am as loath, and as backward as any man to give credit to such instances, which seem rather prodigies, than the phenomena of nature, yet because they often occur in history, it is at least fitting to bring them under further inquiry and examination, that if they can be confuted as false, so much may be done for posterity; and that we at least may not leave on our registers assertions not true, if they can be fairly set aside.

The first sort of them are those which tell us of iron having fallen in great masses, and also in powder after the manner of rain, out of the air. In a part of Italy it rained iron in such a year, and in Germany a great body of iron-stone fell at such a time; the like Avicenna affirms. Julius Scaliger says he had by him a piece of iron, which was rained in Savoy, where it fell in divers places. Cardan reports that 1200 stones have fallen from heaven, and one of them weighed 120lb., some of them 30lb., some 40lb., very hard, and of the colour of iron

Now this ferrum, or as nubigenum, if there was ever any such, was concreted of the breath of the pyrites, which we have elsewhere shown to be the pyrites ex tota substantia. The other instance, which I say is recorded in our registers, is of lightning being magnetic. This I am sure of, I have a petrified piece of ash, which is magnetic; that is, the pyrites in succo; which makes it probable it may be magnetic also in vapour.

On the Production and Effects of Hail, Thunder, and Lightning. By DR. WALLIS, 1697.

Thunder and lightning are so very like the effects of fired gunpowder, that we may reasonably judge them to proceed from like causes. The violent explosion of gunpowder, attended with the noise and flash, is so like that of thunder and lightning, as if they differed only as natural from artificial: as if thunder and lightning were a kind of natural gunpowder, and this a kind of artificial thunder and lightning. Now the principal ingredients in gunpowder, are nitre and sulphur, the admixture of charcoal being chiefly to keep the parts separate, for the better kindling of it. So that if we suppose in the air, a convenient mixture of nitrous and sulphureous vapours, and those by accident to take fire, such explosion may well follow as in the firing of gunpowder. And being once kindled, it will run on from place to place, as the vapour leads it, as in a train of gunpowder.

This explosion, if high in the air, and far from us, will do no mischief, or not considerable; like a parcel of gunpowder fired in the open air; but if near us, or among us, it may kill men or cattle, tear trees, fire gunpowder, break houses, or the like, as gunpowder would do in the like circumstances.

Now this distance may be estimated by the interval of time between seeing the flash of lightning and hearing the noise of the thunder. For though in their generation they be simultaneous, yet, light moving faster than sound, they come to us successively. I have observed that, commonly, the noise is about seven or eight seconds after the flash, that is, about half a quarter of a minute; but sometimes much sooner, in a second or two, or less, and almost immediately on the flash. And at such times, the explosion must needs be very near us, or even among us. In such cases, I have more than once presaged the mischievous consequences, which happened accordingly.

Now, that there is in lightning a sulphureous vapour, is manifest from the smell which attends it, especially when mischief is done, and even when there is none, from the lightning itself, which is more or less discernible. And a sultry heat in the air, is commonly a forerunner of lightning, soon after to ensue. And that there is also a nitrous vapour with it, we may reasonably judge, because we know not of any body so liable to a sudden and violent explosion.

Now as to the kindling of these materials, in order to such explosion, chemits observe, that a mixture of sulphur, filings of steel, and a little water, will not only cause a great effervescence, but will of itself break out into an actual flame. So that there wants only some chalybeate or vitriolie vapour, or something equivalent, to produce the whole effect, there being no want of aqueous matter in the clouds. And there is no doubt, but that among the various effluvia from the earth, there may be copious supplies of matter for such mixtures. And it is known that hay, if laid up too green, will not only heat, but take fire of itself.

The same account may also be given of Ætna, and other burning mountains, where the admixture of steel and sulphur may give a flame, which is often attended with prodigious explosions and earthquakes, from the great quantities of nitre, as in springing a mine.

This may also suggest something as to the generation of hail, which is very often an attendant on thunder and lightning. It is well known, in our artificial congelations, that a mixture of snow and nitre, or even common salt, will cause a present and very sudden congelation of water. And the same in clouds may cause that of hail-stones. And the rather, because not only in those prodigiously great, but in common hail-stones, there seems something like snow, rather than ice, in the middle of them. And, as to those in particular so very large as to weigh half a pound, or three quarters of a pound, supposing them to fall from a great height, it is very possible, that though their first concretion, upon their sudden congelation, might be but moderately great, as in other hail; yet in their long descent, if the medium through which they fall were alike inclined to congelation, they might receive a great accession to their bulk, and divers of them incorporate into one, like as in those icicles before mentioned.

Some Additions to a former Letter on Thunder and Lightning. By Dr. WALLIS, 1697.

When I said, in my former letter, "A mixture of sulphur and filings of steel, with the admission of a little water, will not only cause a great effervescence, but will of itself break forth into an actual fire;" I said expressly, a little water, because too much water will hinder the operation, or quench the fire; which I take to be the case of the Bath waters, where steel and sulphur cause a great effervescence, but no flame. And the like of other hot springs. I do not confine it to this particular mixture, for the chemists, I presume, may furnish us with divers others. I therefore said "or somewhat equivalent." But I gave instance of this for one. I would have added also, that the same account may be given of Etna, and other burning mountains, where the mixture of steel and sulphur may give a flame; which is often attended with prodigious explosions and earthquakes, from great quantities of nitre, as in springing a mine.

On a Whirlwind: in a Postscript of a Letter, dated Aug. 4, 1694, from Warrington, in Northamptonshire, to a Rev. Divine in London.

On the first instant, there happened here, between one and two o'clock in the afternoon, a very terrible whirlwind. It took up into the air about 80 or 100 shocks of corn, carrying a great deal quite out of sight, the rest it scattered about the field, or on the tops of the houses or neighbouring trees. I have seen corn, which was carried a mile from the field; and it is reported by perons of good credit, that some was carried four or five miles distant. The whirlwind continued in Acremont Close full half an hour; I myself, and several other persons, saw at least three or four waggon-loads of corn all at once whirled about in the air.

MAGNETIC PHENOMENA.*

Magnetical Experiments. By M. COLEPRESS, 1667.

I TOOK an unpolished loadstone, which attracted but weakly; and heated a lath nail glowing hot, nimbly applying the north pole of the said magnet to it, which quickly took it up and held it suspended a great while. I took the same stone and cast it into the fire, letting it remain there till it was thorough hot; I applied the north pole to another lath nail cold and untouched before, which it took up but faintly, yet held it suspended for some time. Two or three days after, I took the same loadstone, and found that it attracted then as strongly as before it was cast into the fire. Whence I inferred, that the fire somewhat lessened its attractive faculty, but did not deprive the stone of it.

Magnetical Variations. By M. PETIT, 1667.

Nothing can be more agreeable to me than to discourse on this subject, especially with the philosophers of England, whence the philosophy of the magnet had its rise, and whence also the principal observations of the change of its declination are come to us; so that it is just that the observations made elsewhere concerning the same should return thither as to its source.

After I had made the experiments that are in Gilbert and others, I made that of the needle's declination on three different meridian lines, which I traced, Anno 1630, in several places of Paris, and found that the needle declined 44 degrees north-east: this I made known here to the curious and to artists, some of whom counted nine or ten degrees, according to the traditions and writings of

Orontius Finens and Castlefranc; others 11 degrees, following Sennertus and Offusius.

You know that Gilbert, though the first who has written rationally on the magnet, asserts towards the end of his book, that if a magnet, altogether round, were placed on a meridian, and its poles so placed as to answer to the poles of the world, and consequently its axis to the axis of the world, the stone would continually of its self turn round in twenty-four hours. Whence he infers that the whole earth, as a great magnet, turns also round about its axis in the same space of time.

To try the truth of this proposition, I caused a magnet to be turned with the powder of emery of a spherical form, with all possible exactness, of 1 inch in diameter; which, on account of its compact and uniform composition, had its three centres of magnitude, gravity, and magnetism all the same, with so much justness, that after I had exactly found the two poles of this stone, I caused two small holes to be made therein, to support it by two points of needles, as by two pivots; which, having put in a meridian of brass, and suspended the ball between them like a little globe, it was so easily moveable that I made it turn every way with a blast only of my mouth, and it stopped indifferently, now in one, then in another place, not any side of it prevailing by its gravity, nor descending as it would have done, if any of them had been heavier than another.

This stone thus prepared, without any defect in virtue or figure, uniform, homogeneous, equilibrated, being adjusted on its meridian, and a horizon so placed on its meridian line, that the poles auswered to the poles of the heavens, the result was that it had not any motion, and a small white mark I had made upon this stone remained still in the same place where I had put it, without turning at all; whence I thought the proposition of Gilbert sufficiently refuted.

This stone, together with a greater one, served also to find out whether the needles touched in different places, nearer to or further from the poles, had different declinations. Which having tried frequently with these, and with other stones, I found no difference at all in the declination of the needles, which in all of them was 4 degrees from the north-eastward. And as I did not suspect that this declination would have changed, having found it to be the same in many places, from Brest in Brittany, to the Valtaline among the Alps, I believe the ancients had ill observed, and that the want of their exactness in respect either of the meridian line or the fabric of their needles, or the division of their circles, was the cause of this defect. But I was soon undeceived of my own error, when I learned a little while after, by letters from England, that Mr. Burrows, Anno 1580, had near London observed the declination of the needle to be 11° 11', as well as Offusius and Sennertus. And that, Anno 1612, Mr. Gunter, professor of the mathematics, had in the same place found the declination much diminished, having then found it but six degrees and lastly, that, Anno 1633, Mr. Gellibrand had found