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hands of workmen in Europe, who did not, it seems, well comprehend the principles of that machine, it was much disfigured in their imitations of it; and one of its main intentions, that of admitting a sufficient quantity of fresh air warmed in entering through the airbox, nearly defeated, by a pretended improvement, in lessening its passages to make more room for coals in a grate. On pretence of such improvements, they obtained patents for the invention, and for a while made great profit by the sale, till the public became sensible of that defect in the expected operation. If the same thing should be attempted with this vase stove, it will be well for the buyer to examine thoroughly such pretended improvements, lest, being the mere productions of ignorance, they diminish or defeat the advantages of the machine, and produce inconvenience and disappointment.

The method of burning smoke, by obliging it to descend through hot coals, may be of great use in heating the walls of a hot-house. In the common way, the horizontal passages or flues that are made to go and return in those walls, lose a great deal of their effect when they come to be foul with soot; for a thick blanket-like lining of soot prevents much of the hot air from touching and heating the brick work in its passage, so that more fire must be made as the flue grows fouler; but by burning the smoke they are kept always clean. The same method may also be of great advanvage to those businesses, in which large coppers or caldrons are to be heated.

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Description of an Instrument for taking down Books

from high Shelves.

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January, 1786. Old men find it inconvenient to mount a ladder or steps for that purpose, their heads being sometimes subject to giddinesses, and their activity, with the steadiness of their joints, being abated by age; besides the trouble of removing the steps every time a book is wanted from a different part of their library.

For a remedy, I have lately made the following simple machine, which I call the Long Arm.

A B, the Arm, is a stick of pine, an inch square and 8 feet long. C, D, the Thumb and Finger, are two pieces of ash lath, an inch and half wide, and a quarter of an inch thick. These are fixed by wood screws on opposite sides of the end A of the arm AB; the finger D being longer and standing out an inch and half farther than the thumb C. The outside of the ends of these laths are pared off sloping and thin, that they may more easily enter between books that stand together on a shelf. Two small holes are bored through them at i, k. EF, the sinew, is a cord of the size of a small goosequill, with a loop at one end. When applied to the machine it passes through the two laths, and is stopped by a knot in its other end behind the longest at k. The hole at i is nearer the end of the arm than that at k, about an inch. A number of knots are also on the cord, distant three or four inches from each other.

To use this instrument; put one hand into the loop, and draw the sinew straight down the side of the arm ; then enter the end of the finger between the book you would take down and that which is next to it. The

laths being flexible, you may easily by a slight pressure sideways open them wider if the book is thick, or close them if it is thin by pulling the string, so as to enter

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H the shorter lath or thumb between your book and that which is next to its other side, then push till the back

your book comes to touch the string. Then draw

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the string or sinew tight, which will cause the thumb and finger to pinch the book strongly, so that you may draw it out. As it leaves the other books, turn the instrument a quarter round, so that the book may

lie flat and rest on its side upon the under lath or finger. The knots on the sinew will help you to keep it tight and close to the side of the arm as you take it down hand over hand, till the book comes to you; which would drop from between the thumb and finger if the sinew was let loose.

All new tools require some practice before we can become expert in the use of them. This requires

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very little.

Made in the proportions above given, it serves well for books in duodecimo or octavo. Quartos and folios are too heavy for it; but those are usually placed on the lower shelves within reach of hand.

The book taken down, may, when done with, be put up again into its place by the same machine.

TO BENJAMIN VAUGHAN.

On the Effects of Lead upon the Human Constitution.

Philadelphia, 31 July, 1786. DEAR FRIEND, I recollect, that, when I had last the pleasure of seeing you at Southampton, now a twelvemonth since, we had some conversation on the bad effects of lead taken inwardly; and that at your request I promised to send you in writing a particular account of several facts I then mentioned to you, of which you thought some good use might be made. I now sit down to fulfil that promise.

The first thing I remember of this kind was a general discourse in Boston, when I was a boy, of a complaint from North Carolina against New England rum, that it poisoned their people, giving them the dry bellyache, with a loss of the use of their limbs. The distilleries being examined on the occasion, it was found that several of them used leaden still-heads and worms, and the physicians were of opinion, that the mischief was occasioned by that use of lead. The legislature of Massachusetts thereupon passed an act, prohibiting, under severe penalties, the use of such still-heads and worms thereafter.

In 1724, being in London, I went to work in the printing-house of Mr. Palmer, Bartholomew Close, as a compositor. I there found a practice, I had never seeni before, of drying a case of types (which are wet in distribution) by placing it sloping before the fire. I found this had the additional advantage, when the types were not only dried but heated, of being comfortable to the hands working over them in cold weather. I therefore sometimes heated my case when the types did not want drying. But an old workman, observing it, advised me not to do so, telling me I might lose the use of my hands by it, as two of our companions had nearly done, one of whom, that used to earn his guinea a week, could not then make more than ten shillings, and the other, who had the dangles, but seven and sixpence. This, with a kind of obscure pain, that I had sometimes felt, as it were in the bones of my hand when working over the types made very hot, induced me to omit the practice. But talking afterwards with Mr. James, a letter-founder in the same Close, and asking him if his people, who worked over the little furnaces of melted metal, were not subject to that disorder; he made light of any danger from the effluvia, but ascribed it to par

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VOL. VI.

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