stately old chesnut tree is very little less, possibly more, than a thousand years old; and yet such vigour remains, it bare nuts anno 1759; from them young trees are raised.

1762, Feb.

Yours, &c.

P. C.

XXXI. Remarkable Phenomenon of the Bath Waters.

A Letter from Dr. D. W. Linden to Dr. Sutherland, at the Hot Wells, Bristol, concerning a remarkable Phenomenon of the Bath Waters.

DEAR SIR,

IN compliance with your request, I send you a brief account of my last examination of the Bath waters. The phenomenon which most struck me, were certain cakes, of a black-. ish colour, which at this time of the year are found floating upon the surface of these waters, and which I had never seen before, having been at Bath only in the winter months, when they do not appear. I had, indeed, heard much of them, and was told that they were a vegetable substance, the conferva gelatinosa; but, upon examination, I found this to be a mistake, and that the black cakes were mineral,

That they are not the conferva gelatinosa is manifest, from their appearing so early as the beginning of May; for the conferva does not appear till July, and it does not flower till August. Besides, the conferva is found only on stagnant waters; and it is absurd to suppose that a mineral hot spring should have any communication with a standing pool, whence it should receive this plant, as it could not receive the plant without such a mixture of the water as would render it cold, and annihilate its virtue: that the Bath water cannot originally produce the plant, is certain; for it is continually in a state of agitation, which renders the growth of it impossible.

Upon a close examination of these cakes, some of which have a greenish hue, I found that those which had lain near the wall for some time undisturbed, had caused a natural crystalization of the salts in the Bath water; and these salts, on some of the walls in the Abbey-house spring, were more than half an inch thick; such a crystalization could not be caused by a vegetable substance.

Having now shewn what these cakes are not, I will tell you what they are; for, upon applying the common vitriolinę

solvent, I found them to be neither more nor less than the mucilagium ferri, or slimy substance, that is always a concomitant of iron-stone, iron-earth, or iron-ore; if there is any medical virtue in iron, it ought to be sought in this slimy substance: and I shall shew, in a Treatise on the Bath waters, which I am now preparing for the press, that the Bath waters derive great medical efficacy from these cakes, especially in external applications.

Those persons who have supposed these cakes to be vegetable, have been deceived into that opinion, by the solid fibrous parts which they have discovered in them, after having washed them from the mud and other extraneous bodies, that have been found mixed with them. But those who are acquainted with practical mineralogy, a science which is essentially necessary to those who undertake the analysis of mineral waters, know, that the slimy substance in iron-ore, when agitated in waters that contain salt, will forin itself into fibres and branches, resembling those of vegetables; and upon this principle it is, that, in curious chymistry, small branches and fibres are formed in liquids by the solution of metals and minerals, and have obtained the name of philosophical trees.

Some experiments, indeed, have been made upon these cakes, by distillation; and it has been presumed, that they are vegetable, because they yield only an insipid water, without any metalline or mineral particles; but this is wholly fallacious and inconclusive; for the mucilagium ferri, or any other metal or mineral, mixed with common or saline water, will, in distillation, yield only an insipid water, without mineral particles, because these particles are prevented from rising in the steam, by their own weight. I am, Sir, yours, &c.

1762, May.

D. W. LINDEN.

XXXII. Account of Fires kindled of themselves.*

THE great consumption of sea coal in the port of Brest made it necessary to form a kind of magazine, constructed of timber and planks rudely joined together, where many hundred chaldron were kept piled in a vast mass, and constantly exposed to the weather. No accident was ever

* From the Memoirs of the Royal Academy of Paris.

known to happen from this manner of keeping coals since it was first used, which was about the year 1681. But some persons took it into their heads, that coal thus exposed to the weather lost some of its quality, and that it would be better to keep it under cover.

While they were deliberating upon the form of the new magazine, somebody remarked that it would be proper to leave a considerable space between the top of the coals and the roof of the building in which they were to be kept, that there might be sufficient room for fresh air; because it frequently happened, that this coal took fire when shut close down in the hold of the vessels that brought it, if the voyage happened to be longer than usual, or the weather so bad that they could not open the scuttles: this opinion, however, was not regarded; the new magazine was built very close and compact, and covered in at the top: it was divided into two equal parts, within, by a wall; one division being called the Magazine, No. I. and the other the Maga zine, No. II.

1

No. I was filled quite to the top, and contained about twelve hundred chaldron: in a very short time afterwards it took fire, which was perceived by the smoke that came out at the chinks of the door. As soon as the door was opened, the smoke burst out in great black clouds, and the labourers, who had been ordered to get the coal out, were obliged to throw great quantities of water upon it, before they could begin to work.

They found a rafter of deal, which was within the building near the door, half burnt; and a beam which the coal touched, in the same condition; they had not flamed, but were burnt quite through to a cinder: the coals that lay on the top of the heap were only warmed by the smoke that had passed through them, but those in the middle had lost their inflammability, and were reduced to a kind of calx; and near the bottom they had suffered no injury, nor even contracted the least heat. About half the coals were then taken out of this magazine; the good were separated from the damaged, and part of them put back again, and the rest put into the other magazinę,

It was now a second time proposed to give the magazines air; and it was urged, that though the coal should not again take fire, yet it would probably grow hot, and lose part of its quality; but the magazine was already built, and they thought all accidents would be effectually prevented, by not filling the magazine to the top; but a great quantity of coals arriving soou after in the port, and not daring to lay

them up in the magazine that had once taken fire already, they yet foolishly filled the other magazine with it quite to the top, without considering that this magazine was then in the same circumstances as those which had caused the accident that happened to the other; the consequence was, that this magazine also in a very short time took fire, and would have done the same damage if it had not been sooner discovered; the top of the heap being hot, the middle in part consumed, and the bottom unaltered. Add to this account another most remarkable instance of the same kind.

The sail cloth generally used in France, is made of coarse hempen thread; after it is woven, it is wetted, and shrunk, as we do our drab cloth, and is then painted on one side only, with red ochre ground with oil.*

On the 18th of July, 1757, the workmen had painted about fourscore yards of this cloth; and the weather being very hot, the sun dried it very soon: on the 20th, about 4 o'clock in the afternoon, the weather changed, and a sudden storm of thunder and rain being expected, the sail-cloth which had been thus milled and painted, was very hastily folded up while it was yet very hot by having lain exposed to the sun, the folds being so managed that the painted side did not come in contact with the other, but with itself only; the folds were pressed very close, that the cloth might lie in the least compass possible, and it was then put up in bales, and deposited, one upon another, in the warehouse, upon a kind of iron grating, the squares of which were about three inches wide, and which was about a foot from the ground: this warehouse is level with the ground, but floored; and it is the custom to place a kind of brasiers, or close chafing dishes of lighted small coal-dust under the grating, to keep the cloth that lies in bales over it perfectly dry, lest being moist in the middle, it should rot; and the warehouse is every night close shut up.

On the 22d, about four in the evening, one of the workmen having been lying some time upon these bales, found

The experiment frequently repeated at St. John's Gate, by mixing a brown earth, found in the mines in Derbyshire, with linseed oil, is worth noting upon this occasion: the result was, that, upon grinding the two bodies together, upon a stone, the whole mass took fire and burnt with a most intense heat till the oil was consumed, and nothing but the dry earth remained. May not other earthy substances so mixed, produce the same effect? It was by grinding this earth with oil to make a paint, that its inflam mable quality was discovered.

them very hot, and putting his hand into one of them between the plaits, it burnt him. The supervisor being immediately acquainted with this accident, caused the bales to be brought out into the air, and upon opening them they sent out a thick smoke: some pretended that they saw a flame, but it is probable that they saw only the sun's rays reflected from the smoke.

It was at first suspected that these bales had been set on fire; the grating was therefore taken up; but after the strictest search, no appearance of fire was found, and it appeared that the suspicion was wholly groundless upon a farther inspection of the bales, for the fire had manifestly begun in the centre of each bale, the outward parts of them having received no injury: the plaits that had been pressed closest by the cord were most damaged, being burnt to a cinder, so as to crumble between the fingers.

Some of the old workmen declared, that the same thing had happened many years ago; but that, conceiving it impossible for the bales to take fire of themselves, they had concealed the accident, for fear of being taxed with negligence, and punished accordingly.

That hay, put up wet, will take fire, is well known to our farmers; and many fires have happened by rain falling on unslacked lime.

1763, Jan.

XXXIII. On the prodigious Growth of Trees,

THERE are giants in the vegetable, as well as the animal kingdom. For proof of which, I shall here recite what I have observed in my reading, concerning monstrous trees, that have deserved the particular notice of travellers and natural

ists.

Thevenot, in his Travels, A.D. 1656, Part I. Chap. 71, tells us, that in the island of Coos, which the Turks call Stranchio, and Lango, or Isola Longa, there is a tree of such a vast extent, that it can easily cover two thousand men, and that the branches of it are supported by several stone and wooden pillars, there being under it several barbers' shops, coffee-houses, and such like, with many benches to sit on, This tree is like a sycamore, but the fruit it bears is like a chesnut, and serves for tanning of leather,