convinced that the evil frequently thus originates, and its prevention would be in using timber previously well dried and seasoned.

Since I communicated the preceding observations relative to the dry rot in timber, I have been busily engaged in draining from 4 to 500 acres of ground, and farther ideas on the subject of the dry rot have recurred to me from the work I have been engaged in, which may probably be worthy of attention.

Where houses are troubled with damp walls, near the earth's surface, it is generally, if not universally, occasioned by the percolation of water from the higher adjoining ground, which, thus intercepted in its current, attempts to follow the general hydrostatic law, of elevating itself, by the syphon line, to a height equal to that from whence it has its origin. Thus in houses differently situated, we see the damp arising, to varying degrees of height, on the walls; and those are probably all corresponding to the height at which the moisture circulates in the adjoining ground. At its first entrance to the building, and whilst the mois. tare is in small quantity, the excavated part of the foundation wall may absorb, and gradually quit such proportion; but the excess, as is generally the case in moist weather, exceeding that power, the foundation stones are then saturated in a more rapid proportion than the adjoining rarefied internal atmosphere can evaporate the watery particles then creep up, in degrees proportionate to the ascent from which they originally descended, excepting when prevented or driven off by the superior heat of the adjoining rooms; wifen, in addition to the

disagreeable damp they catise, they frequently occasion considerable damage to pictures, furniture, &c. Drains laid out athwart the ascending ground, with a very slight descent or fall, and made of the depth of one yard for each yard of ascent, and from the foundation until equal to the height that such damp ever rises, would, there is little doubt, completely secure the house and furniture from the inconveniencies hitherto sustained, and would generally prove an effectual prevention to most cases of the dry rot, where it originates in extreme moisture. I am of opinion that the fungus which pervades decaying wood is not the first cause, but an attendant on the peculiar state to which such wood bas been reduced by prior causes. The disseminated seeds finding a proper bed, or nidus, like to the mushroom, toadstool, &c. fix there their abode, and pervade the whole substance, thus accelerating the general law of providence, which tends to make all matter reproductive.

Cellars, or such other places, should be drained in the manner Í have above mentioned, by taking off the percolating water, prior to its gaining admission to, or contact with, the walls; and it is probable that, in most cases, a single drain will have a complete effect; it would assuredly do so, if it was not for the variation of the earth's interna strata, which are not easily discernable. If attention to this rule. was paid prior to the building any new streets or towns, it would prove essentially useful.

from lime-stone. Chalk-lime attracts moisture; and communfeating it to any timber which it touches, occasions its decay. Sea-sand is also prejudicial, if made into mortar, from a similar quality of attracting moisture from the atmosphere: this may in some degree be corrected by washing the sand well in fresh water, where good sand cannot be procured..

Good mortar, where any is required to be in contact with timber, may be made from a mixture of stone-lime fresh burnt, and river. sand, to which a very small quantity of common brown or yellow iron ochre, should be added, and well incorporated therewith.

The following is a description of an invention, by Mr. Robert Seppings, late master ship-wright assistant in his majesty's yard at Plymouth, (now master-shipwright of his majesty's yard at Chatham,) for suspending, instead of lifting, ships, for the purpose of clearing them from their blocks; by which a very great saving will accrue to the public; and also two-thirds of the time formerly used in this operation.From the saving of time another very important advantage will be derived, that of enabling large ships to be docked, suspended, and undocked, the same spring tides.Without enumerating the inconvemiencies arising, and perhaps injurics which ships are liable to sustain, rom the former practice of lifting

them, and which are removed by the present plan; that which relates to manual labour deserves particular attention; twenty men being suffi cient to suspend a first rate, wherea it would require upwards of five hundred to lift her. The situation which Mr. Seppings held in Ply. mouth yard, attached to him, in a great degree, the shoring and lifting of ships, as well as the other practical part of the profession of a shipwright. Here he had an opportu rity of observing, and indeed it was a subject of general regret, how much time, expence, and labour, were required in lifting a ship, par. ticularly ships of the line. This in. duced him to consider whether some contrivance could not be adopted to obviate these evils. And it oc

curred to him, that if he could so construct the blocks on which the ship rests, that the weight of the ship might be applied to assist in the operation, he should accomplish this very desirable end. In September, 1800, the shoring and lifting the San Josef, a large Spanish first-rate, then in dock at Plymouth, was committed to his directions; to perform which, the assistance of the principal part of the artificers of the yard was requisite. In conduct. ing this business, the plan, which will be hereafter described, occur. red to his mind; and from that time, he, by various experiments, proved his theory to be correct: the blocks constructed by him, upon which the ship rests, being so con trived, that the facility in removing them is proportionate to the quantity of pressure; and this circum stance is always absolutely under command, by increasing or diminishing the angle of three wedges, which constitute one of the blocks;

two of which are horizontal and one vertical. By enlarging the angle of the horizontal wedges, the vertical wedge becomes of consequence more acute; and its power is so increased, that it has a greater tendency to displace the horizontal wedges, as can be proved by a model*, where the power of the screw is used as a substitute for the pressure of the ship.

Mr. Seppings caused three blocks to be made of hard wood, agreeable to his invention, and the wedges of various angles. The horizontal wedges of the first block were nine degrees, of the second seven, and of the third five; of course the angle of the vertical wedge of the first block was 162 degrees, of the second 166, and of the third 170. These blocks or wedges were well execúted, and rubbed over with soft soap for the purpose of experiment. They were then placed in a dock, in his majesty's yard at Plymouth, in which a sloop of war was to be docked; on examining them after the vessel was in, and the water gone, they were all found to have kept their situations, as placed before the ship rested upon them. Shores in their wake were then crected to sustain the ship, prior to the said blocks being taken from under the keel. The process of clearing them was by applying the power of battering-rams to the sides of the outer ends of the horizontal wedges, alternate blows being given fore and aft, by which means they imme diately receded, and the vertical wedges were disengaged. It was observed, even in this small ship, that the block which was formed of horizontal wedges of nine degrees, came away much easier than

those of seven, and the one of seven than that of five. In removing the aforesaid blocks by the power of the battering rams, which were suspended in the hands of the men employed, by their holding ropes passed through holes for that purpose, it was remarked by Mr. Seppings, that the operation was very laborious to the people, they having to support the weight of the battering-rams, as well as to set them in motion. He then conceived an idea of affixing wheels near the extremity of that part of the rams which strikes the wedges. This was done before the blocks were again placed; and it has since been found fully to answer the purpose intended, particularly in returning the horizontal wedges to their original situations, when the work is performed for which they were displaced; the wheels also giving a great increase of power to the rams, and decrease of labour to the artificers; besides which, the blows are given with much more exactness. The same blocks were again laid in another dock, in which a two-decked ship of the line was docked. On examination, they were found to be very severely pressed, but were removed with great ease. They were again placed in another dock, in which a three-decked ship of the line was docked. This ship having in her foremast and bowsprit, the blocks were put quite forward, that being the part which presses them with the greatest force. soon as the water was out of the dock, it was observed, that the ho rizontal wedges of nine and seven degrees, had receded some feet from their original situations. This af forded Mr. Seppings a satisfactory proof, which experience has since 3 K 4

As

dcmon.

demonstrated, (though many persons before would not admit of, and others could not understand, the principle,) that the facility of removing the blocks or wedges was proportionate to the quantity of pressure upon them. The block of five degrees kept its place, but was immediately cleared, by applying the power of the battering-rams to the sides of the outer ends of the horizontal wedges. The above experiments being communicated to the navy-board, Mr. Seppings was directed to attend them, and explain the principle of his invention; which explanation, farther corroborated by the testimonials of his then superior officers, was so satisfactory, that a dock was ordered to be fitted at Plymouth under his immediate directions. The horizontal wedges in this, and the other docks that were afterwards fitted by him, are of cast-iron, with an angle of about five degrees and a half, which, from repeated trials, are found equal to any pressure, having in no instance receded, and when required were easily removed. The vertical wedge is of wood, lined with a plate of wrought iron, half an inch thick. On the bottom of the dock, in the wake of each block, is a plate of iron three quarters of an inch thick, so that iron at all times acts in contact with iron.

The placing the sustaining shores, the form and sizes of the wedges and battering rams, &c. also the process of taking away, and again replacing the wedges of which the block is composed, are also exemplified by a model.

The dock being prepared at Plymouth, in August, 1801, the Cano pus, a large French eighty-gun ship, was taken in, and rested upon the blocks; and the complete success

of the experiment was such, that other docks were ordered to be fitted at Sheerness and Portsmouth dock yards under Mr.Sepping's directions. At the former place a frigate, and at the latter a three-decked ship were suspended in like manner. This happened in December, 1802, and January, 1803; and the reports were so favourable, as to cause directions to be given for the general adoption of these blocks in his ma jesty's yards. This invention being thought of national consequence, with respect to ships, but particularly those of the navy, government has been pleased to notice and reward Mr. Seppings for it.

The time required to disengage each block, is from one to three mi nutes after the shores are placed; and a first rate sits on about fifty blocks. Various are the causes for which a ship may be required to be cleared from her blocks, viz. to shift the main keel, to add addition. al false keel, to repair defects, to caulk the garboard seams, scarples of the keel, &c. Imperfections in the false keel, which are so very in. jurious to the cables, can in the largest ship be remedied in a few hours by this invention, without adding an additional shore, by taking away blocks forward, amidships, and abaft, at the same time; and when the keel is repaired in the wake of those blocks, by returning them into their places, and then by taking out the next, and so in succession. The blocks can be replaced in their original situations, by the application of the wheel batteringrams to the wedges, the power of which is so very great, that the weight of the ship can be taken from the shores that were placed to sustain her. There were one hun dred and six ships of different clas

es lifted at Plymouth dock-yard, rom the 1st of January, 1798, o the 31st of December, 1800, nd had the operation of lifting aken less time, the number would ave been very considerably inreased; for the saving of a day is ery frequently the cause of saving he spring-tide, which makes the dif erence of a fortnight. The import

nce of this expedition in time of var, cannot be sufficiently estimated.

This invention may be applied vith great advantage, whenever it is ecessary, to erect shores to support any great weights, as, for instance, to prop up a building during the repair of its foundation, &c. Captain Wells, of his majesty's ship Glory, of 98 guns, used wedges of Mr. Sepping's invention, for a fid of a top gallant-mast of that ship. In 1803, the top gallant-masts of the Defence, of 74 guns, were fitted on this principle by Mr. Seppings; and from repeated trials, since she has been cruising in the North Sea, the wedge fids have been found in every respect to answer.

But it is Mr. Seppings's wish, that it should be understood, that the idea of applying his invention to the fid of a top-gallant-mast, originated with captain Welis, who well understood the principle, and had received from him a model of the invention.

When it is required to strike a top-gallant-mast, the top ropes are hove tight, and the pin which keeps the horizontal wedges in their place is taken out by one man going aloft for that purpose; the other horizontal wedge is worked in the fid. The upper part of the fid hole is cut to form the vertical wedge. The advantage derived from fidding topgallant-masts in this way is, that

they can be struck at the shortest notice, and without slacking the rigging, which is frequently the cause of springing and carrying them away, particularly those with long pole heads. The angle of the horizontal wedges for the fids of masts, should be about twenty degrees.

Account of the Processes for Dyeing the beautiful Reds on the Coromandle Coast; communicated by J. Machlachlan, Esq. of Calcutta.

The following receipts for dyeing the beautiful reds of the Coromandel coast, were sent to me from Madras by a scientific friend, who had the several operations detailed in them performed in his own presence. I forwarded a copy of them, and a small quantity of the ingredients mentioned in them, to a friend at home, several years ago; but he dying about or soon after the time of their arrival, I never learned what became of them. It strikes me, however, that there is a considerable coincidence between the thread process and that which I have seen recommended by Mr. Henry of Manchester, for dyeing the Adrianople or Turkey red.

I am not certain whether it is known at home, that many of the hills in Bahar, and other parts of India, contain immense quantities of mica, talc, or Muscovy glass. The natives of this country and China,' make very splendid lanterns, shades, and ornaments of it, tinged of various fanciful colours; and it is also used by them in medicine. When burned or calcined, it is, I am told, considered as a specific in obstinate coughs or consumptions. When powdered, it serves to silver the