than five feet; the lower series of beams should be planked outside, the same as the rest of the vessel, which thus forming the bottom of a third vessel in the midst of the other two, should slope gradually upwards at either end, that it might both make less resistance to the waves, and tend to rise over them when it encountered them. This middle vessel, instead of being entirely sustained by the other two, might be constructed so as to draw a foot or two of water, which would both case the strain on the others greatly, keep up the head of the vessel against the depressing impulse of the sails, prevent the sudden and violent percussions which a flat surface, suspended at a small distance above the waves, must suffer from them in rough weather, and afford stowage for cables and a number of articles, without the bad effect of loading on a part entirely unsupported by the water, which it otherwise must experience. The middle vessel, besides the superior conveniences which it would afford for stowage and lodging for the crew, would also give great security in case of a dangerous leak taking place in either of the side vessels for by it the whole could be so sustained, occasionally, that it might be brought safe into port, though one of the side vessels was entirely water-logged. Double vessels, of a large size, should not be made to go with either end foremost; for, besides the impossibility of staying the masts properly for this purpose in them, they could not thus be shaped to the greatest advantage for sailing swift; for the head requiring a certain fullness to bear up against the impulse of the sails, and the stern a certain run, or length of slope, the head also requiring the sloping or rounding off to be sidewise, and the stern requiring the run, or sloping, to be mostly from the bottom upwards, the shape which would be fit for one would not be fit for the other, and an intermediate shape would not be perfect either way. Small double vessels may have the platform greatly strengthened by two or more pair of shears erected across it, each well secured to the deck by a perpendicular shroud descending to it from the upper angle, or by a mast rising in that part, well bolted to the platform below, and firmly fastened to the shears above: it is imagined the shears in the first of Sir Sydney's boats might have been for this purpose. In concluding, it is proper to notice another species of vessels, projected by Mr. Gordon before mentioned, which he averred would have all the good properties of the double vessels, be much stronger, have much more stowage, and require less timber in their construction; and which certainly are worthy of a fair trial. These vessels were to be very flat, draw very little water, and have their capacity in length and breadth chiefly ; and to prevent making leeway, they were to have beneath their flat bottoms a number of deep narrow keels, three or four feet from each other, and were to be furnised with two or more rudders each, if one was not found sufficient for their management. On the cleaning of Engravings with oxygenated muriatic Acid. By M. J. L. Roard J. L. Roard. From the Bibliotheque Physico-Economique. the smallest. By these means they may be the more easily extended. and in taking them out they are not liable to be torn. Having put on the cover, pour at the same time the water and the oxygenated muriatic acid into the leaden tube, which must then be taken out, that the apparatus may be exactly closed. Let the engravings be in whatever state they may, they are commonly clean in two or three hours, which may be ascertained by examining one of those placed in the centre. That the operator may not be in commoded by the smell, when the bleaching is finished, he must tum the cock, which, by means of a pipe, conducts the liquor into a larg covered vessel, placed under the ap paratus; but as the gas and the acid with which the engravings are still impregnated might render the labour inconvenient, and even dan. gerous, it must be again filled with pure water. If the prints are ca strong paper, they may be take one by one out of the water; but if they are thin and much worn, it h better to draw off the liquid, and to let them harden. They are the laid to drain on hurdles, covered with linen cloths; after which they are washed on both sides with plenty of water, either on inclined marble slabs, or on frames of white cloth. This operation is very essential, for the engravings sometimes turn yel low again very soon, when they have not been sufficiently washed. They are then spread on hurdles. provided with napkins, or on paste. board covered with white paper: and that they may not dry too quickly, they should neither be exposed to the sun nor to a stron current of air. While yet a little damp they are laid between two For this purpose it is necessary to have a small conical cask of deal, one metre in height, and fifty or sixty centimetres in diameter, provided with wooden hoops. Adjust to it a lid, closing hermetically, and a double moveable bottom, on which place the engravings, which are separated, and supported by very fine glass tubes, rounded with care at the lamp. To mix the water properly with the muriatic acid, pour them both, by means of a funnel, into a large leaden pipe, which passes through the cover, and ests on the double bottom. Before the engravings are placed in the apparatus destined for cleaning them, they are divided into two parts; the first comprises those that are greasy, such as are glued on canvass, or pasted on paper; the second, those that are only stained and spotted with ink. Having placed all those of the first class in an earthen vessel, or a small cask of deal, fill it with a warm and very weak solution of potash, or a solution which may be procured by the lixiviation of ashes. Two or three hours are sufficient to take out all the spots the liquor is then emptied out, and replaced with clear water, in order to remove all the alkaline parts which would contribute to weaken the oxygenated muriatic acid. The water being drawn off, and the engravings having become dry, place them in the bleaching-vessel, concentrically, either lengthwise or breadthwise, according to their dimensions, in the spaces left between the tubes, and so as not to be too much crowded, first introducing the Jargest, and reserving the middle for 2 shoew 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 whatever, 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 stuif 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 cousiderable, 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 smell of the substance that caused it. Hence it is to be pre sumed, 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, ex tends 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 over head, 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 nine 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 uder the bed of the sea. The mine of Huel-Cok has been abandoned for about fifteen years past, on account of the danger which continually became LOR menacing. But a work much more enter. prising than any related, was one executed in the midst of the sea it. self, near the port of Penzance, in Cornwall, about a century ago. At low water in this place, a gravelly bottom was left bare, in which was discovered a multitude of small veins of tin ore, which crossed each other in every direction. The adjacent rock also contained this mineral in considerable quantities: they worked this rock whenever the sea, the time, and the season would permit, until the depth became too great. There is nothing known more of this mine to any certainty till about fifteen years since, when a poor miner in the neighbourhood undertook the work anew, and conti nued it with a degree of intelligence and perseverance which cannot be sufficiently admired. Before relating the plans which he formed, and the success with which he followed them, I will endeavour to give some idea of the difficulties he had to conquer, and of the obstacles which nature seemed to oppose to him. The place where the tin ore is found is in the midst of the sea, about 200 yards from the shore; and as the bank of the sea in this place is very steep and high, this distance is not less considerable at low water. This place is covered by the sea at high water six yards deep; and as the bottom is very gravelly and full of rocks, the waves become much agitated, and rise to a great height, when the wind blows from particular points. This inconvenience enience takes place all the winter, ad has always caused the failure of te different attempts which have een made before to erect engines › drain the mine and raise the ore. t low water the rock rises a little bove the surface of the sea; nevereless, there is not teu months of 1y year in which it is uncovered. Against all these difficulties a aman creature had to contend, hose whole property was not orth fifty crowns. This couraous miner employed three sumers in sinking a pit, during which me he could only work two hours day, and every time when he went > work found his excavation full of ater. This he was obliged to mpty out before he would touch e work, which occasioned still reater difficulties when he set about lasting it. At first he had only need of trength and patience; but when e sunk to a greater depth he added o them ingenuity. He built round he mouth of his pit a turret of Food impervious to water, and by his means was able to prolong the ime of working on the rock. He arther endeavoured to shut out the ea entirely from his pit, by raising he turret above the greatest height to which the sea could reach. 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 nei ther the flux or reflux of the sea, or the shocks of the waves could overturn it: the enterprising miner had provided against these difficulties; by good chance the rock was a por. phyry, 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 Stokwork, 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. Το 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 his 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 ter, |