botanists, as appears from their publications; but they are known to the Germans, who have habitually used more wood in their buildings than we have.

I had lately a conversation with an old friend, who shewed me two parcels of rotten wood, from an oak barn floor, laid about sixteen years ago. After lying twelve years it shook upon the joists. On examination, it was found to be rotted in various parts, and the planks, two inches and a half in thickness, were nearly eaten through, though the outside was glossy, and without blemish. The joists and a large middle beam were laid at the ends, in brick and mortar, to create a firm level. No earth was near the wood; and he thinks that no air could find a passage. The rotten ness was partly an impalpable powder, of the colour of Spanish snuff, and other parts were black, as if burnt; the rest was clearly a fungus. This gentleman is a per. son of undoubted veracity, but a nic and exact observation is necessary in such examinations. He thought nothing of any plant, and it is likely there was none of the boletus; so that my assertion, that it was always to be found,was rather too systematic.

I asked him if the timber was dry when laid down, he could not however say that it had been particularly adverted to. It had been sawed from a large oak, and was, as he thought, in all respects proper for a barn floor. As this seems not the operation of the boletus, how did it happen?

We know that the oak, when in vegetation, is subject to what I shall call an exudation of juices, which produces the fungus, named the

agaric of the oak, with which the druids of old played many tricks. The oak then, if sawed into thick quantities, may emit these same juices, as the progressive course of nature to its entire decay.

We have all seen oaks of vast size and ancient record, with a great part of the outside whole, and all the inside gone; perhaps the work of a century. In all hollow trees fungus is discoverable. To use a law term, it is a misnomer to call it dry rot; for the rotting principle is in moisture.

I had never seen the rot upon so large a scale as in timber, till lately. The prevention then of beams, rafters, large joists, and posts put into the earth, from decay by the rot, is in charring only, which will dry up all the fungus juices of wood in large substance. Paint, a betumenous preparation, may probably stop up the pores, and prevent the rot in slight work, where the treatment I before observed, with fire, might be incommodious, as in half inch wainscot, &c. incorruptibility of charcoal is attested by undoubted historical facts, at the destruction of the famous temple at Ephesus. It was found to have been erected on piles that had been charred; and the charcoal in Herculaneum, after almost 2000 years, was entire and undiminished.

Mr. Bramley's communication.

The

As the society for the encouragement of arts, &c. have for some years offered a premium for the discovery of the cause occasioning the dry rot in timber, of which it seems no satisfactory account has yet been received; should the following prove so, it will give the author much plea3 K 2

sure.

sure.

To bring the matter to the test by experiments would require the observation of a long period, and in selected situations.

Wood used for the general purposes of man, is cut down at different periods; and although it may be felled at the proper season, or when most free from sap or mois-ture, it is not always to be effected.

Even admitting it to have been cut down in the most favourable situation, it still abounds with such an extra proportion of moisture, as to require a regular exposure to the air, prior to its being applied to use, if we wish to guard against that shrinking, which always takes place, where this precaution has not been taken.

Although the fir kind contains less of this watery portion, yet it assuredly possesses a considerable share; and it is in this species, I apprehend, that the evil called the dry rot most generally occurs, as from the facility of working the same, it is most generally applied in buildings.

But supposing it to be fir, or any other species; wood felled when abounding with any extra proportion of sap, and applied to use with out the proper seasoning or exposure to a free current of air, until such extra moisture has had time to exhale, is most liable to the disease in question; and the cure, or principal prevention against it, would be the precaution of felling all wood only at the proper season, or when the sap is not in circulation. The next mode of prevention would be to use such wood only, as has been for a considerable period exposed to the influence of a free current of air, or where convenience will admit, to

that of air heated to a moderate de gree; such air extracting with great, er facility the inclosed moisture, and in a more certain ratio than the irregularity of our atmosphere will allow.

In all rapidly improving countries, this evil is likely to be an increasing one, as the current demand for wood generally exceeds the supplies laid by in store, so as to be applied to use in regular succession, after being properly seasoned. Another cause that affects all wood most materially, when not fully dried, is the application of paint, the nature of which prevents all exhalation, and confines the enclosed moisture, till it occa sions a fermentation through the whole fibrous system of the wood, and brings on a premature state of decomposition, or the dry rot.

A similar evil may be induced, in consequence of any newly finished building having all the doors and windows shut up, and that for some length of time, particularly in moist weather. The wood, even though unpainted, is thus frequently placed in an atmosphere more charged with vapour than its own internal con tents, and is consequently in an imbibing instead of an exhaling state, and tending to decay. Wood placed in dampish situations, and the ends of timbers near to moist walls, suffer from similar causes.

What particularly attracted my observation to the circumstances was this, that both ash and fir posts were brought into this premature state of decay, from their having been painted prior to the due evaporation of their moisture; and then extending the observation, and tracing the history of other wood affected in a similar manner, I am convinced

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 en gaged 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. ture 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; when, in addition to the

disagreeable damp they cause, 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 has 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 I 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 communicating it to any timber which it touches, occasions its decay. Sca-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 riversand, 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 pub lic; 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 inconveniencies arising, and perhaps injuries which ships are liable to sustain, from 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, whereas 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 nity 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 induced 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 per form 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, upoa which the ship rests, being so contrived, that the facility in removing them is proportionate to the quan tity of pressure; and this circum. stance is always absolutely under command, by increasing or dimi nishing 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 acnte; 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 executed, 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 erected 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 immediately 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. As soon as the water was out of the dock, it was observed, that the horizontal wedges of nine and seven degrees, had receded some feet from their original situations. This afforded Mr. Seppings a satisfactory proof, which experience has since 3 K 4

demon