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stacks, the opening of each as a funnel is impracticable. This change of manners soon consumed the fire-wood of England, and will soon render fuel extremely scarce and dear in France, if the use of coals be not introduced in the latter kingdom, as it has been in the former, where it at first met with opposition; for there is extant in the records of one of Queen Elizabeth's Parliaments a motion made by a member, reciting, “That many dyers, brewers, smiths, and other artificers of London, had, of late, taken to the use of pit-coal for their fires, instead of wood, which filled the air with noxious vapors and smoke, very prejudicial to the health, particularly of persons coming out of the country; and therefore moving that a law might pass to prohibit the use of such fuel (at least during the session of Parliament) by those artificers.” It seems it was not then commonly used in private houses. Its supposed unwholesomeness was an objection. Luckily, the inhabitants of London have got over that objection, and now think it rather contributes to render their air salubrious, as they have had no general pestilential disorder since the general use of coals, when, before it, such were frequent. Paris still burns wood at an enormous expense, continually augmenting; the inhabitants having still that prejudice to overcome. In Germany you are happy in the use of stoves, which save fuel wonderfully: your people are very ingenious in the management of fire, but they may still learn something in that art from the Chinese, whose country, being greatly populous and fully cultivated, has little room left for the growth of wood, and, having not much other fuel that is good, have been forced upon many inventions, during a course of ages, for making a little fire go as far as possible. I have thus gone through all the common causes of the smoking of chimneys that I can at present recollect as having fallen under my observation; communicating the remedies that I have known successfully used for the different cases, together with the principles on which both the disease and the remedy depend, and confessing my ignorance wherever I have been sensible of it. You will do well, if you publish, as you propose, this letter, to add in notes, or, as you please, such observations as may have occurred to your attentive mind; and, if other philosophers will do the same, this part of science, though humble, yet of great utility, may in time be perfected. For many years past, I have rarely met with a case of a smoky chimney which has not been solvable on these principles, and cured by these remedies, where people have been willing to apply them; which is indeed not always the case, for many have prejudices in favor of the nostrums of pretending chimney doctors and fumists, and some have conceits and fancies of their own, which they rather choose to try than to lengthen a funnel, alter the size of an opening, or admit air into a room, however necessary; for some are as much afraid of fresh air as persons in the hydrophobia are of fresh water. I myself had formerly this prejudice, this aérophobia, as I now account it; and, dreading the supposed dangerous effects of cool air, I considered it as an enemy, and closed with extreme care every crevice in the rooms I inhabited. Experience has convinced me of my error. I now look upon fresh air as a friend; I even sleep with an open window. I am persuaded that no common air from without is so unwholesome as the air within a close room that has been often breathed and not changed. Moist air, too, which formerly I thought pernicious, gives me now no apprehensions; for, considering that no dampness of air applied to the outside of my skin can be equal to what is applied to and touches it within, my whole body being full of moisture, and finding that I can lie two hours in a bath twice a week, covered with water, which certainly is much damper than any air can be, and this for years together, without catching cold, or being in any other manner disordered by it, I no longer dread mere moisture, either in air or in sheets or shirts; and I find it of importance to the happiness of life, the being freed from vain terrors, especially of objects that we are every day exposed inevitably to meet with. You physicians have of late happily discovered, after a contrary opinion had prevailed some ages, that fresh and cool air does good to persons in the small-pox and other fevers. It is to be hoped that in another century or two we may all find out that it is not bad even for people in health. And, as to moist air, here I am at this present writing in a ship with above forty persons, who have had no other but moist air to breathe for six weeks past; everything we touch is damp, and nothing dries, yet we are all as healthy as we should be on the mountains of Switzerland, whose inhabitants are not more so than those of Bermuda or St. Helena, islands on whose rocks the waves are dashed into millions of particles, which fill the air with damp, but produce no diseases, the moisture being pure, unmixed with the poisonous vapors arising from putrid marshes and stagnant pools, in which many insects die and corrupt the water. These places only, in my opinion,--which, however, Isubmit to yours, – afford unwholesome air; and, that it is not the mere water contained in damp air, but the volatile particles of corrupted animal matter mixed with that water, which renders such air pernicious to those who breathe it. And I imagine it a cause of the same kind that renders the air in close rooms, where the perspirable matter is breathed over and over again by a number of assembled people, so hurtful to health. After being in such a situation, many find themselves affected by that febricula which the English alone call a cold, and, perhaps from the name, imagine that they caught the malady by going out of the room, when it was in fact by being in it. You begin to think that I wander from my subject, and go out of my depth. So I return again to my chimneys. We have of late many lectures in experimental philosophy. I have wished that some of them would study this branch of that science, and give experiments in it as a part of their lectures. The addition to their present apparatus need not be very expensive. A number of little representations of rooms, composed each of five panes of sash-glass, framed in wood at the corners, with proportionable doors, and movable glass chimneys, with openings of different sizes, and different lengths of funnel, and some of the rooms so contrived as to communicate on occasion with others, so as to form different combinations, and exemplify different cases; with quantities of green wax taper cut into pieces of an inch and half, sixteen of which, stuck together in a square, and lit, would make a strong fire for a little glass chimney, and, blown out, would continue to burn, and give smoke as long as desired. With such an apparatus, all the operations of smoke and rarefied air in rooms and chimneys might be seen through their transparent sides; and the effect of wind on chimneys, commanded or otherwise, might be shown by letting the entering air blow upon them through an opened window of the lecturer's chamber, where it would be constant while he kept a good fire in his chimney. By the help of such lectures our fumists would become better instructed. At present, they have generally but one remedy, which perhaps they have known effectual in some one case of smoky chimneys; and they apply that indiscriminately to all the other causes, without success, – but not without expense to their employers. With all the science, however, that a man shall suppose himself possessed of in this article, he may sometimes meet with cases that may puzzle him. I once lodged in a house at London, which, in a little room, had a single chimney and funnel. The opening was very small, yet it did not keep in the smoke, and all attempts to have a fire in this room were fruitless. I could not imagine the reason, till at length observing that the chamber over it, which had no fireplace in it, was always filled with smoke when a fire was kindled below, and that the smoke came through the cracks and crevices of the wainscot, I had the wainscot taken down, and discovered that the funnel which went up behind it had a crack many feet in length, and wide enough to admit my arm, -a breach very dangerous with regard to fire, and occasioned probably by an apparent irregular settling of one side of the house. The air, entering this breach freely, destroyed the drawing force of the funnel. The remedy would have been filling up the breach, or rather rebuilding the funnel; but the landlord rather chose to stop up the chimney. Another puzzling case I met with at a friend's country-house near London. His best room had a chimney in which, he told me, he never could have a fire, for all the smoke came out into the room. I flattered myself I could easily find the cause, and prescribe the cure. I had a fire made there, and found it as he said. I opened the door, and perceived it was not want of air. I made a temporary contraction of the opening of the chimney, and found that it was not its being too large that caused the smoke to issue. I went out and looked up at the top of the chimney; its funnel was joined in the same stack with others, some of them shorter, that drew very well, and I saw nothing to prevent its doing the same. In fine, after every other examination I could think of, I was obliged to own the insufficiency of my skill. But my friend, who made no pretensions to such kind of knowledge, afterwards discovered the cause himself. He got to the top of the funnel by a ladder, and, looking down, found it filled with twigs and straw cemented by earth, and lined with feathers. It seems the house, after being built, had stood empty some years before he occupied it; and he concluded that some large birds had taken advantage of its retired situation to make their nest there. The rubbish, considerable in quantity, being removed, and the funnel cleared, the chimney drew well and gave satisfaction. In general, smoke is a very tractable thing, easily governed and directed, when one knows the principles, and is well informed of the circumstances. You know I made it descend in my Pennsylvania stove. Much more of the prosperity of a winter country depends on the plenty and cheapness of fuel than is generally imagined. In travelling, I have observed that in those parts where the inhabitants can have neither wood, nor coal, nor turf, but at excessive prices, the working people live in miserable hovels, are ragged, and have nothing comfortable about them. But when fuel is cheap (or where they have the art of managing it to advantage) they are well furnished with necessaries, and have decent habitations. The obvious reason is, that the working hours of such people are the profitable hours, and they who cannot afford sufficient fuel have fewer such hours in the twentyfour than those who have it cheap and plenty; for much of the domestic work of poor women, – such as spinning, sewing, knitting, —and of the men in those manufactures that require little bodily exercise, cannot well be performed where the fingers are numbed with cold; those people, therefore, in cold weather, are induced to go to bed sooner, and lie longer in a morning, than they would do if they could have good fires or warm stoves to sit by ; and their hours of work are not sufficient to produce the means of comfortable subsistence. Those public works, therefore, such as roads, canals, &c., by which fuel may be brought cheap into such countries from distant places, are of great utility; and those who promote them may be reckoned among the benefactors of mankind. I have great pleasure in having thus complied with your request, and in the reflection that the friendship you honor me with, and in which I have ever been so happy, has continued so many years without the smallest interruption. Our distance from each other is now augmented, and nature must soon put an end to the possibility of my continuing our correspondence; but, if consciousness and memory remain in a future state, my esteem and respect for you, my dear friend, will be everlasting.