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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.
Written at Sea, 1785.
Description of an Instrument for taking down Books from high Shelves.
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. E F, 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
the shorter lath or thumb between your book and that which is next to its other side, then push till the back of your book comes to touch the string. Then draw