fixed on the top of the pipe, the end of which correfponding with the aperture below, the fame vertical plane will pafs through the lever and the ftream. Small engines, fuch as thofe ufed for watering gardens, will be fuflicient for the purpofe. Two men only will be required for the fervice of each pipe, one to fupply it, and the other to direct the stream. JOHN READ. Royal Military Repofitory, Woolwich. An Improvement on Metallic Con ductors or Lightning-rods. From the Amer. Phil. Tranf. ROM the inftances which now FROM and then occur of houfes being ftruck with lightning, that are furnished with metallic conductors, and the frequent inftances of thefe conductors having their tops melted off by a ftroke of lightning, it appears that this admirable contrivance for guarding houfes against the dangerous effects of lightning is, in fome degree, ftill imperfect. Some improvement feems yet to be wanting at both extremities of the rod at the upper extremity, to fecure it against the accident of being melted, which renders it afterwards unfit to anfwer its original intention, viz. drawing off the electric fluid. or light ning, from the paffing cloud, in a filent, imperceptible manner; for it is only pointed conductors that poffefs this property-and at the lower extremity, to afford a more ready paflage for the fluid into the furrounding earth. The firit of thefe intentions would, I am perfuaded, be effectually anfwered, by inferting in the top of the rod a piece of black 4 lead, of about two inches long, taken out of a good pencil, and terminating in a fine point, projecting but a very little above the end of its metallic focket; fo that, if the black lead point fhould happen to be broken off by any accident, of which however I think there can be but little danger, ftill the point of the rod would be left fharp enough to answer the purpose of a metallic conductor. This fubftance is well known to be infufible by the greatest heat, and hence its ufe in making crucibles; nor is it evaporable, as remarked by Cronstedt, in his mineralogy, fec. 231, except in a flow calcining heat, to which it could never be expofed on the top of a lightning-rod. At the fame time its power as a conductor of electricity is perhaps. equal, or but little inferior, to that of any of the metals. A line drawn on a piece of paper by a blacklead pencil will, as I have often experienced, conduct an electric explofion feemingly as well as a fimilar line of gilding would do, and that without ever lofing its conducting power, which is not the cafe with gilding. The fecond intention is to facilitate the efcape of the electric fluid from the lower part of the rod into the furrounding earth. It is, in many cafes, impracticable, from the interruption of rocks and other obftacles, to fink the rod fo deep as to reach moist earth, or any other fubftance which is a tolerably good conductor of electricity. Nor even if this were practicable, would it, I prefume, be alone fufficient to answer the defired intention. Iron buried in the earth, and especially in moift earth, will presently contra& contract a coat of ruft, which will continually increase till the whole is converted into ruft: but ruft of iron, and indeed the calx of all metals, is a non-conductor, or at moft but a very imperfect conductor of the electric fluid. Hence it is eafy to fee, that in a few years after a lightning-rod has been erected, that part of it which is under ground will contribute little or nothing towards the fafety of the building Befides, the furface of this part of the rod is too small to afford an eafy and copious difcharge of the electric fluid into the furrounding earth, when this is but an imperfect conductor. As a remedy for thefe defects, I would propofe, that the part of the rod under ground be made of tin, or copper, which are far lefs liable to corrosion or ruft, by lying under ground, than iron. Or, which per better, let this part of the rod, of whatever metal it be made, be coated over with a thick cruft of black lead, previously formed into the confiftence of pafte, by being pulverized and mixed with melted fulphur (as in the manufactury of the ordinary kind of black lead pencils) and then applied to the rod while hot. By this means, the lower part of the rod would I apprehend, retain its conducting powers for ages, without any dimi nution. In order to increase the furface of the lower part of the conductor, let a hole or pit, of fufficient extent, be dug as deep as convenient; and into this pit let there be put a quantity of charcoal, round the lower extremity of the rod. Charcoal poffeffes two properties which, in a peculiar manner, fit it for anfwering the purpose here in view. First, it is a very good conductor of electricity; and fecond, it will undergo little or no change of property by lying ever fo long in the carth. Thus might the furface of that part of the conductor, in contact with the earth, be increafed, with little trouble or expence, to any extent at pleasure; a circumftance which every one acquainted with electrical experiments muft acknowledge to be of great importance to the end here propofed. R. PATTERSON. Effects of Mud, as a Manure, by Thomas Walford, Efq. From the Annals of Agricul. vol. xix. Dear Sir, Ου OU mention, in your Annals, page 431, the great benefit the Rev. Mr. Walford, of Boreham, received from pond mud, " frefl from a pond, the foil of which is an imperfect moory peat, on a gravelly loam." I beg leave to lay before you three experiments with mud upon an upland pafture, laid down with graffes about eight years, the mud from a moat, the bottom of which is a white marly clay. In September 1790, I caft the moat, one end of which adjoins the farm yard, and had received the draining from it eighteen or nineteen years; this part, I was advised (contrary to my own opinion of its being proper) to cart immediately upon the land, and fpread it as foon as it was dry enough: I did fo-and the effect was, infinite injury to the fuccceding crop of grafs; it caked down fo very firm, that the rain and froft, that feafon, with the affift. ance of a great deal of labour, did not pulverize it fufficient for the grafs to get through. The lofs I fuftained was very confiderable, there being lefs hay than on any other part of the field. The following year I was much inclined to have harrowed it, with a heavy pair of harrows, and fow it again with feeds: I did not; yet am convinced the crop would have been more productive if I had; for it was very light, and not equal to the crop before the mud was carried on. The third year, being a wet feafon, it began to work, and produced me a tolerable burthen, but not fufficient to repay the lofs of the two former; yet the benefit was very vifible, for the fpot where it was laid might be traced to great exactness. The mud from the other parts of the moat was thrown upon the banks and left to drain; this I wifhed to have let remain there a year, to have ftirred it over, and then carried it upon the pasture, but was again prevailed upon to carry on two parts out of three as foon as it was dry enough to cart; being told it would fave a confiderable expence, and be equally beneficial, in both of which I was difappointed; the extra expence of buth-harrowing, and beating the clods to pieces, was more than the ftirring over would have been; for, like the former, it caked down, and injured, instead of benefiting the fucceeding crop of grafs, but not in fo great a degree-for I thought fome advantage was derived from it the fecond year. As the two methods above were quite contrary to my ideas and opinion, I was determined with the mud that remained to adopt the following plan of my own, which probably may not be new in many other places, although it is in this parith. Inftead of carting the mud when dry, I turned it over with a spade, except about one rod at the end, which, from fome caufe or other, was neglected till March; I then dug it and planted potatoes. The other part, from having had the winter's froft and rains, was very full of mould, and I imagined would do exceedingly well for carrots; it was fown with carrots; but whether the drynefs of the feafon, badness of feed, or the foil not being proper (the latter I believe), my crop was a very bad one; but the potatoes exceeded my expectation; had the whole been planted with them, the produce would have doubly paid me the expence of digging and planting; and the mud received great benefit, by being ftirred over when they were taken up. When the crops were cleared, I carted the mud upon the poorest part of the pasture, and was agreeably furprifed to find it produced a very fine crop of grafs the June following, fuperior to many parts of the field that had been well manured at the fame time. The luxuriance of the crop was fo confpicuous, as to attract the attention of the neighbouring farmers. Therefore, having met with fuch great fuccefs from the latter experiment, I fhall in future empty my ponds between hay-time and harveft, let the mud lie till it is dry enough to dig, then ftir it over, and in March dibble in potatoes; being convinced, if it is not the beft method to adopt, it is a profitable one, where the mud is taken from a clay bottom. I am, Sir, Your obedient humble fervant, THOMAS WALFORD. An eafy and expeditious Method of diffipating the noxious Vapour commonly found in Wells and other fubterraneous Places, by E. Robinfon. From the Amer. Phil. Tranf. FTER various unfuccefsful been already communicated) I was led to confider, how I could convey a large quantity of fresh air from the top to the bottom of the well; fuppofing that the foul would neceffarily give way to the pure air. With this view I procured a pair of finith's bellows fixed in a wooden frame, so as to work in the fame manner as at the forge. This apparatus being placed at the edge of the well, one end of a leathern tube (the hofe of a fire engine) was clofely adapted to the note of the bellows, and the other end was thrown into the well, reaching within one foot of the bottom. At this time the well was fo infected, that a candle would not burn at a fhort distance from the top; but after blowing with my bellows only half an hour, the candle burned bright at the bottom; then, without further difficulty, I proceeded in the work, and finished my well. Wells are often made in a very flight manner, owing to the diffi culty of working in them, and there have been feveral fatal inftances of the danger attending the workmen; but by the above method there is neither difficulty nor danger in completing the work with the utmoft folidity. It is obvious, that in cleanfing vaults, and working in any other fubterraneous places, fubject to damps, as they are called, the fame method muft be attended with the fame beneficial effect, A Method of draining Ponds in level AT Ta certain distance below the furface of the earth, there is a ftratum of loofe fand which freely admits the paffage of water. This ftratum is at various depths, in different elevations; but it will be generally found, that lands most fubject to ftagnant ponds, have but a thallow ftratum of clay over the fand. All that is neceffary, therefore, is to dig a pit in the bottom of the pond, till you arrive at this ftratum of fand, when the water will be immediately abforbed, and the pond emptied. Should there be too much water to permit a hole to be dug within the pond, it may be made at the edge of it, the communication afterwards made by a trench. It would be prudent not to make the fides of the pit fo fteep, as to prevent cattle from getting out, fhould they happen to go in. The writer does not pretend to be the original author of this invention; the idea was fuggefted to him, by feeing it practifed by a farmer, who enjoyed the benefit, though he did not appear to know the caufe. Account Account of the Inventor and Invention of the Art of hardening and polishing Leather. FOR OR the art of hardening and polishing leather, and the manufacturing of various implements and utenfils from it, fuperior for many uses to thofe formed of other materials, the world is indebted to Gavin Wilson, a journeyman bootmaker, of the city of Edinburgh. The extenfive circulation of the polithed leathern powder-flasks, drinking-mugs, fouff-boxes, ink-cafes, and numerous other useful articles in this branch of manufacture, of which he was the original maker, has rendered this invention famous not only over Europe, but in other quarters of the globe, although the name of the inventor is almoft entirely unknown. His abilities were not limited to the producing of the articles in this line of manufacture which are in common ufe; his ingenuity enabled him to form a German flute and a violin, both of leather, which for neatnefs of workmanship and melodioufnefs of tone were neither of them inferior to any inftruments of the fame kind, formed of wood, by the workmen whofe peculiar province it is to make thefe inftruments. The exertions of his genius went yet farther, and he contrived artificial arms and legs of the fame materials, which not only remedied the deformity arising from the want of a natural limb, but in a great meafure fupplied that lofs, in itself one of the moft diftreffing that can befal any individual. The unexampled fuccefs of his endeavours in this way, and the very imminent advantages the maimed derived from his inventions, may be beft inftanced by a letter, written by a perfon who was unfortunate enough to be deprived of both his hands while ferving in the royal navy by the affiftance of Gavin Wilfon this man was enabled both to convey his fentiments by writing, and to perform many useful offices about his own perfon. The letter was firft published in the Caledonian Mercury, for 1779, along with an advertifement of the ingenious mechanic who was the means of rendering this author a comfort to himself, and in fome measure an useful member of fociety. Were any farther teftimony requifite to evince the high utili. ty of this deferving artift's contrivances, befides the approbation of the patriotic board which honoured his ingenuity by a premium, the authority of two of the most celebrated medical practitioners of the prefent age might be produced; Dr. Alexander Monro, prefent profefior of anatomy and furgery in the univerfity of Edinburgh; and Mr. Benjamin Bell, author of the Syftem of Surgery, published at Edinburgh. Dr. Monro, in his lectures for thefe many years paft, has annually honoured the memory of Gavin Wilfon with a public encomium, as the inventor of the improved artificial arms and legs; and Mr. Bell, in the fixth volume of the work above mentioned, pays the following tribute to his merit. "Thefe artificial legs and arms are preferable to any I have ever feen. The leg, when properly fitted, proves equally useful with the common timber-leg, and is preferable for being neater; at the Lame |