the fociety for infpection. I hope that this useful inftrument may become univerfal, as navigation certainly will be rendered more fafe through its means; and I shall think myself highly honoured, if through the channel of this fociety it becomes public. Letter concerning Smoky Chimneys, to his Excellency Benjamin Franklin, Efq. LL.D. Prefident of the State of Penfylvania, and of the American Philofophical Society, &c.-From the fame Work. SIR, TH Philadelphia, January 12, 1786. HE fubject of fmoky chimneys, of which I had the honour of converfing with you at your own houfe laft evening, is of fo much importance to every individual, as well as to every private family, that too much light cannot be thrown upon it. A fmoky house and a fcolding wife, of the year 1777, it happened to be my lot to dwell in an old manfion which had been recently modernifed, and had undergone a thorough repair. But as in most of the old houfes in England the chimneys, which were perhaps originally built for the purpose of burning wood, though they had been contracted in front, fince coal fires came into general ufe, to the modern fize, yet they were still above, out of fight, of building chimneys may perhaps extravagantly large. This method have answered well enough while it was the custom to fit with the doors and windows open; but when the customs and manners of the people, began to be more polished and refined, when building and architecture were improved, and they began to conceive the idea of making their chambers clofe, warm, and comfortable, thefe chimneys were found to fmoke abominably, for want of a fufficient fupply of air. This was exactly the cafe with the houfe in which I first lived, near Exeter, and I was under the necef Are (faid to be) two of the greateft ills in fity of trying every expedient I life. And however difficult it may be to remedy one of thofe ills, yet any advances we may be able to make towards removing the inconveniences arifing from the other, cannot fail to be favourably received by the public. As they are fhortly to be favoured with your fentiments on that fubject, poffibly the following obfervations, which were in fact occafioned by neceffity, and are the refult of my own experience, may not be altogether undeferving of notice. When I left London and went to live in Devonshire, in the latter end could think of to make it habitable. The first thing I tried, was that method of contracting the chimneys by means of earthen pots, much in ufe in England, which are made on purpose, and which are put upon the tops of them; but this method by no means anfwered. I then thought of contracting them below, but as the method of contracting them in front to the fize of a small coal-fire grate has an unfightly appearance, as it makes a difagreeable blowing like a furnace, and as it is the occafion of confuming a great deal of unneceffary fuel, the heat of which is immediately hur G 3 ried ried up the chimney, I rejected this method, and determined to contract them above, a little out of fight. For this purpofe, I threw an arch acrofs, and alfo drew them in at the fides. This had fome effect, but as this contraction was made rather faddenly, and the smoke, by ftriking against the corners that were thereby occafioned, was apt to recoil, by which means fome part of it was thrown out into the room; I determined to make the contraction more gradually, and therefore run it up at the back, where the depth of the chimney would admit of it, and alfo fhelving or floping in a conical kind of direction at the fides, as high as a man, ftanding upright, could conveniently reach, and by this means brought the cavity within the space of about twelve by fourteen or fixteen inches, which I found fufficiently large to admit a boy to go up and down to fweep the chimneys. This method I found to fucceed perfectly well, as to curing the chimneys of fmoking, and it had this good effect of making the rooms confiderably warmer; and as this experiment fucceeded fo well, fince the only ufe of a chimney is to convey away the fmoke, I determined to carry it ftill farther, in order to afcertain with precifion how much pace is abfolutely neceffary for that purpose, becaufe all the relt that is fhut up must be fo much gained in warmth. Accordingly I laid a piece of flate across the remaining aperture, removable at pleafure, fo as to contract the space above two thirds, leaving about three inches by twelve remaining open; but this fpace, except when the fire burnt remarkably clear, was fcarcely fufficient to carry away the fmoke. I therefore enlarged it every room of it fmoked. My predeceffor, who was the first inhabitant, had been at great expence in patent ftoves, &c. but without effect; but by adopting the method I have just now defcribed, I not only cured every chimney of fmoking, but my house was remarked for being one of the warmest and moft comfortable to live in of any in that large and opulent city. : The houfe I now live in, in Philadelphia, I am told, has always had the character of being both cold and fmoky; and I was convinced, as foon as I faw the rooms and examined the chimneys, that it deferved that character; for tho the rooms were clofe, the chimneys were large and we thall ever find, that if our chimneys are large, our rooms will be cold even though they fhould be tolerably clofe and tight; because the conftant rushing in of the cold air at the cracks and crevices, and alfo at every opening of the door, will be fufficient to chill the air, as faft as it is heated, or to force the heated air up the chimney; but by contracting the chimneys I have cured it of both thefe defects. There was one remarkable circumftance attending the contraction of the chimney in the front parlour, which deferves to be attended to; which was, that before I applied the cast-iron plate, which I made ufe of inftead of flate, to diminish the space requifite for a chimney Chimney-fweeper's boy to go up and down, the fuction or draught of air was fo great, that it was with difficulty I could fhut the door of the room, infomuch that I at firft thought it was owing to a tightness of the hinges, which I imagined must be remedied, but upon applying the iron plate, by which the fpace was diminished one half, the door fhut to with the greatest eafe. This extraordinary preffure of the air upon the door of the room, or fuction of the chimney, I take to be owing in fome measure to the unufual height of the house. Upon the whole, therefore, this fact feems clearly ascertained, viz. 'That the flue or fize of the chimney ought always to be proportioned to the tightnefs and clofe nefs of the room; fome air is undoubtedly neceffary to be admitted into the room in order to carry up the fmoke, otherwife, as you juftly obferved, we might as well expect fmoke to arife out of an exhaufted receiver; but if the flue is very large, and the room is tight, either the fmoke will not afcend, the confequence of which will be, that the air of your room will be fo frequently and fo conftantly changed, that as fast as it is heated it will be hurried away, with the fmoke, up the chimney, and of courfe your room will be conftantly cold. One great advantage attending this method of curing fmoky chimneys is, that, in the firft place, it makes no awkward or unfightly appearance, nothing being to be feen but what is ufual to chimneys in common; and in the fecond place, that it is attended with very little expence, a few bricks and mortar, with a plate or covering to the aperture, and a little labour, being all that is requifite. But in this new country, where crops of houfes may be expected to rife almost as quick as fields of corn, when the principles upon which chimneys are erected ought to be thoroughly underfood, it is to be hoped, that not only this expence, fmall as it is, but that all the other inconveniences we have been speaking of, will be avoided, by conftructing the flues of the chimneys fufficiently fmall. From your humble fervant, THOMAS RUSTON. A Letter from the Reverend Jeremy SIR, A Dover, New-Hampshire, MONG the number of efcu lent roots; the parfiip has two fingular good qualities. One is, that it will endure the feverest froft, and may be taken out of the ground in the fpring, as fresh and fweet as in autumn; the other is, that it may be preferved by drying, to any defired length of time. The first of these advantages has been known for many years paft; the people in the moft northerly parts of New-England, where winter reigns with great feverity, and the ground is often frozen to the depth of two or three feet for four months, leave their parsnips in the ground till it thaws in the fpring, and think them much better preferved than in cellars. The other advantage never occurred to me till this winter, when one of my neighbours put into my hands a fubftance which had the appearance G 4 appearance of a piece of buck's horn. This was part of a parsnip which had been drawn out of the ground last April, and had lain neglected in a dry clofet for ten months. It was fo hard as to re, quire confiderable ftrength to force a knife through it cross-wife; but being foaked in warm water, for about an hour, became tender, and was as fweet to the tafte as if it had been fresh drawn from the ground. As many useful difcoveries owe their origin to accident, this may fuggeft a method of preferving fo pleasant and wholefome a vegetable for the use of feamen in long voyages, to prevent the fcurvy and other diforders incident to a fea-faring life, which is often rendered tedious and diftreffing for want of vegetable food; fince I am perfuaded that parfnips dried to fuch a degree, as above related, and packed in tight cafks, may be tranfported round the globe, without any lofs of their flavour or diminution of their nutritive quality. I am, Sir, moift air, and to part with it as readily to a dry air. Different fubftances have been found to poffefs more or less of this quality; but when we shall have found the fubftance that has it in the greatest perfection, there will ftill remain fome uncertainty in the conclufions to be drawn from the degree fhown by the inftrument, arifing from the actual ftate of the inftrument itself as to heat and cold. Thus, if two bottles or veffels of glafs or metal being filled, the one with cold and the other with hot water, are brought into a room, the moisture of the air in the room will attach itself in quantities to the surface of the cold veffel, while if you actually wet the furface of the hot veffel, the moifture will immediately quit it, and be abforbed by the fame air. And thus in a fudden change of the air from cold to warm, the inftrument remaining longer cold, may condenfe and abforb more moisture, and mark the air as having become more humid than it is in reality, and the contrary in a change from warm to cold. But if fuch a fuddenly changing inftrument could be freed from these imperfections, yet when the defign is to difcover the different degrees countries, I apprehend the quick of humidity in the air of different fenfibility of the inftrument to be rather a difadvantage; fince, to draw the defired conclufion from it, a conftant and frequent obfervation day and night in each country will be neceffary for a year or years, and the mean of each different fet of obfervations is to be found and determined. After all which, fome uncertainty will remain refpecting the different degrees of exactitude with which different perfons may have made and taken notes of their obfervations. For these reasons, I apprehend, that a fubftance which, though capable of being diftended by moifture and contracted by drynefs, is fo flow in receiving and parting with its humidity, that the frequent changes in the atmosphere have not time to effect it fenfibly, and which therefore fhould gradually take nearly the medium of all thofe changes and preferve it conftantly, would be the most proper fubftance of which to make fuch an hygrometer. Such an inftrument, you, my dear fir, though without intending it, have made for me; and I, without defiring or expecting it, have received from you. It is therefore with propriety that I addrefs to you the following account of it; and the more, as you have both a head to contrive and a hand to execute the means of perfecting it. And I do this with greater pleafure, as it affords me the opportunity of renewing that ancient correfpondence and acquaintance with you, which to me was always fo pleafing and fo inftructive. You may poffibly remember, that in or about the year 1758, you made for me a fet of artificial magnets, fix in number, each five and a half inches long, half an inch broad, and one eighth of an inch thick. Thefe, with two pieces of foft iron, which together equalled one of the magnets, were inclofed in a little box of mahogany wood, the grain of which ran with, and not acrofs, the length of the box; and the box was clofed by a little fhutter of the fame wood, the grain of which ran across the box; and the ends of this shutting piece were bevelled fo as to fit and flide in a kind of dovetail groove when the box was to be fhut or opened. I had been of opinion that good mahogany wood was not affected by moisture fo as to change its dimenfions, and that it was always to be found as the tools of the workman left it. Indeed the difference at different times in the fame coun-. try is fo fmall, as to be fcarcely in a common way obfervable. Hence the box, which was made fo as to allow fufficient room for the magnets to flide out and in freely, and, when in, afforded them fo much. play, that by fhaking the box one could make them ftrike the oppofite fides alternately, continued in the fame ftate all the time I remained in England, which was four years, without any apparent alteration. I left England in Auguft 1762, and arrived at Philadelphia in October the fame year. În a few weeks after my arrival, being defirous of fhowing your magnets to a philofophical friend, I found them fo tight in the box, that it was with difficulty I got them out; and conftantly during the two years I remained there, viz. till November 1764, this difficulty of getting them out and in continued. The little fhutter too, as wood does not fhrink lengthways of the grain, was found too long to enter its grooves, and not being ufed, was miflaid and loft; and I afterwards had another made that fitted. In December 1764 I returned to England, and after fome time I oblerved that my box was become full big enough for my magnets, and too wide for my new fhutter; which was fo much too fhort for its grooves, that it was apt to fall out; and |