sheets of fine paper, on which are placed pasteboards of the same dimensions. Thus arranged, they are disposed one above the other, and put into the press, where they must remain at least twenty-four hours. When the engravings are very valuable, they may be put into the press with plates of copper of the same size as the print itself, which imparts to them the highest degree of beauty and freshness. Care must afterwards be taken to expose them to the air and to the sun, to dissipate entirely the smell of the oxygenated muriatic acid, and not to put them into port-folios till they are perfectly dry. In spite of all the above-mentioned precautions, there may remain on the backs of those which were glued yellow spots, produced by the action of the oxy. genated muriatic acid on the animal matter of the glue; but these may easily be removed by sulphuric acid. By the method here stated, I have cleaned several hundreds of engravings in one day, notwithstanding the extraordinary pains I was obliged to bestow on such a great number of very rare and valuable prints, almost all of which were proof impressions, such as the battles of Alexander, some of the most beautiful landscapes by Woollett, &c. Method of removing Spots of Grease. M. Lenormand has discovered a new and easy method of instantly removing spots of oil, grease, and tallow, from any kind of stuff what-, ever, without changing its colour. Take five or six pieces of lighted charcoal, about the size of a wal nut; wrap them in a piece of white and very clean linen, which has been previously dipped in water, and squeezed in the hand to press out the super-abundant water. Extend the stuff that is spotted on a table, on which a very clean napkin has first been spread; then take the cloth containing the charcoal by four corners, and lay it upon the spot. Lift it up and put it down again on the spot ten or twelve times successively, pressing lightly upon it, and the spot will entirely disappear. When the spot is considerable, it sometimes goes through the stuff, and the grease or oil is imbibed by the napkin. But whether this is the case or not, when you lay the charcoal on the spot a thick vapour rises from it, which has the sinell of the substance that caused it. Hence it is to be presumed, that the heat diffused by the burning charcoal volatilizes the water of the cloth in which they are wrapped, and thus decomposes the grease and oil, which it reduces to vapours. So much, however, is certain, that no spot of the abovementioned nature has ever resisted this process. Account of Submarine Mines in Cornwall, by Mr. Hawkins. The mine of Huel-Cok, in the parish of St. Just, in Cornwall, which descends eighty fathoms, extends itself forward under the bed of the sea beyond low-water-mark. In some places the miners have only three fathoms of rock between them and the sea; so that they hear very distinctly the movement and the noise of the waves. This noise is sometimes terrible, and of an extraordinary traordinary loudness; the Atlantic ocean having here many hundred leagues breadth. In the mine the rolling of the stones and rocks overhead, which the sea moves along its bed, is plainly heard; the noise of which, mixed with the roaring of the waves, sounds like reiterated claps of thunder, and causes both admiration and terror to those who have the curiosity to go down. In one place, where the vein was very rich, they searched it with imprudence, and left but four feet of rock between the excavation and the bed of the sea. At high water the howling of the waves is heard in this place in so dreadful a manner, that the miners who work near it have often taken to flight, supposing that the sea was going to break through the weak roof, and penetrate into the mine. Dr. Stukeley relates, that a coalmine at Whitehaven is advanced so far under the sea, at a depth of 150 fathoms, (a depth greater than that of any part of the channel between England and Ireland,) that vessels pass over the heads of the miners. Between the mine and the sea there is a considerable mass of matter. A very wonderful circumstance at Huel-Cok is, that in some places, under the bed of the sea, where there is only a small thickness of rock between the mine and the sea, in one place not more than four feet, there does not enter into the mine but a very small quantity of water by leakage: when the miners perceive any chinks, which might give it a passage, they stop them up with clay, or with oakum. The like method is used in the lead-mines of Para Zabulon, which also run under the bed of the sea. The mine of Huel-Cok has be abandoned for about fifteen ye past, on account of the dang which continually became me menacing. But a work much more entr prising than any related, was executed in the midst of the sea self, near the port of Penzance, Cornwall, about a century At low water in this place gravelly bottom was left bare which was discovered a multitude small veins of tin ore, which crose each other in every direction. I adjacent rock also contained mineral in considerable quantitie they worked this rock whenever sea, the time, and the season wo permit, until the depth became great. There is nothing known more this mine to any certainty till abo fifteen years since, when a pat miner in the neighbourhood unde took the work anew, and comf nued it with a degree of intellige and perseverance which cannot sufficiently admired. Before rela ting the plans which he formed, the success with which he follow them, I will endeavour to give some idea of the difficulties he had to cot quer, and of the obstacles whi nature seemed to oppose to him. The place where the tin or found is in the midst of the about 200 yards from the shore) and as the bank of the sea in thi place is very steep and high, th distance is not less considerable. low water. This place is cover by the sea at high water six yard deep; and as the bottom is verf gravelly and full of rocks, the wares become much agitated, and rise to great height, when the wind blowt from particular points. This incon Tenicac venience takes place all the winter, and has always caused the failure of the different attempts which have been made before to erect engines to drain the mine and raise the ore. At low water the rock rises a little above the surface of the sea; nevertheless, there is not ten months of any year in which it is uncovered. Against all these difficulties a human creature had to contend, whose whole property was not worth fifty crowns. This courageous miner employed three summers in sinking a pit, during which time he could only work two hours a day, and every time when he went to work found his excavation full of water. This he was obliged to empty out before he would touch the work, which occasioned still greater difficulties when he set about blasting it. At first he had only need of strength and patience; but when he sunk to a greater depth he added to them ingenuity. He built round the mouth of his pit a turret of wood impervious to water, and by this means was able to prolong the time of working on the rock. farther endeavoured to shut out the sea entirely from his pit, by raising the turret above the greatest height to which the sea could reach. He But here he had new difficulties to conquer; first to make this turret impervious to water, and secondly to stay it in such a manner that neither the flux or reflux of the sea, or the shocks of the waves could overturn it the enterprising miner had it: provided against these difficulties; by good chance the rock was a porphyry, not too hard to cut, but still very firm. He shaped the portions he separated from it, and disposed them in a regular manner, at the bottom of the turret, and closed and calked with oakum and fat cement all the interstices between the wood and the stone, so that the whole was united into one mass. The pit, like all those in Cornwall, was lined with planks; all the joints were well calked and payed with pitch. When his frame-work was thus raised, he supported it with iron braces. He formed then about the mouth of the pit, so raised, a platform of planks, which rested on four great piles, and fixed on it a windlass, worked by four men. This work, as may be imagined, took much time, and met with many mishaps in the execution; but the perseverance and presence of mind of the undertaker conquered all obstacles. When the pit and tower were finished, he then reaped the fruit of his industry, and established a regular work at Stok. work, drew from it in a little time a considerable quantity of tin, and put his adventure on a very good footing. But sometimes this undertaking was not in such a good state. To save expence, and diminish his labours, he attacked the part of the mine overhead; by which means at high water the sea penetrated through the chinks of the rock, so that he was obliged to sustain the roof, which was extensive, in some parts, by planks and thick props, to prevent the great mass of water, which pressed on it above, from driving it in. Besides this, notwithstanding bis pains and endeavours, it was not possible for him to keep his wood-work water-tight in the winter; and when the sea was rough he could not transport the ore ashore in his boat. He was forced to desist from the work all the win Four men in two hours emptied the pit of water by the windlass, at the rate of four tons in a minute; towards the end of which time six men drove it from the bottom of the pit, and poured it into the passage. After drawing off the water they worked six hours more on the rock. From one tide to another they raised about thirty sacks of ore, each sack containing fourteen gallons; fifteen sixteenths of which were so rich that they produced one-sixth of a hundred weight of tin, and one-sixteenth of a hundred was procured from the remaining part; so that in six months they raised to the value of 600l. sterling of tin. As most of the ore was interspersed in a hard rock, diflicult to pound, the undertaker had it roasted in a common lime-kiln, which answered perfectly well. There was nothing of this kind done in Cornwall before. What I have related is what I myself saw of this singular work, which is known by the name of Huel-ferry. One of my friends, who is in that part of the country, wrote me as follows, in 1792. "We have hopes that the work on the vein of ore mixed with "porphyry will become hereafter <6 very profitable. It is found on both sides of the pit for a great The mischief arising in buildings from that decay in the timber and wood work, known in general by the name of the dry rot, has been, and yet continues so great as to de mand every attention for its prevention. Some valuable facts furnished by Robert Batson, esq. of Limehouse, respecting the methods he took to prevent this evil, in one of his rooms greatly affected by it, claims particular notice. The plan he adopted was to charr the ends of his timbers, to take away the in fected fected earth to the depth of two feet, and to fill up that space with anchor-smiths' ashes, or ashes from a foundery, before his flooring boards were laid. On the 15th of May 1794, which was upwards of six years after the flooring was laid, as above mentioned, a minute exa. mination of the boards, wainscot, and timbers was made in the presence of a committee of the society for the encouragement of arts &c. and they were all found entirely free from any appearance of the rot. To investigate the matter more fully, a farther enquiry has been made in June, 1803, and an answer received, that there has been yet no appearance of the dry rot there; the society, therefore, think it may be of consequence to notice the fact, and have inserted, in the last volume, some other papers with which they have been favoured upon the subject. They contain many hints deserving public attention, and which will doubtless tend to check the progress of this evil. Mr. Johnston's communication. Some time between 1771 and 1773, I went, at the request of a friend, to the chapel at the Lock hospital, through curiosity, to examine a pew there, that had frequently been repaired for damages by the dry rot. After a close investigation, we found that it was the operation of a plant, whose leaf resembled that of the vine. Wherever it had touched, the effect of its poisonous quality got through the wood to the paint, which I have seen a mere skin. I proposed to cover the floor with bricks laid in mortar, which was accordingly done. I called twice since, the last time about seven VOL. XLVII, years ago; and have reason to think that it had never appeared again. The next opportunity of examining it carefully was at Mark Hall, in Essex, the seat of Mr. Montague Burgoyne. In a parlour there were three pillars of about ten inches in diameter, the out wood of which was between two and three inches thick. Two of them were eaten through in less than seven years, from the basis about two feet upward, within the hollow, and were as rotten as if it had been the effect of a hundred years standing. Mr. Montague Burgoyne's gardener was a botanist: he found the plant where I directed him to search for it; and he said it was the boletus lachrymans. At another time, I saw it in a house at White Hall, built by sir John Vanburgh, whose nephew then lived in it. The house is, I think, only two stories high; the plant had ascended to the upper story, committing devastation on the wainscot all the way. It will destroy halfinch deal wainscoting in a year. I have had it twice in houses I inhabited, one in Suffolk, and the other in Gloucestershire. I bore with the first; in the other case, I undertook, and did stop it effectually. The cause is from the floor being laid on the earth, which has been, where I have observed, of a gravelly or sandy loam. The moisture from a water course at hand, or a north aspect, where the outer wall stands in a garden bed, so that the rain percolates, are great encouragers; it requires moisture. It never rises in the middle of the floor; because, if the seed were there, it could not germinate for 3 K want |