Lectures on Select Subjects in Mechanics, Hydrostatics, Pneumatics, Optics and Astronomy (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1837 Excerpt: ...by its spring or elasticity, through the hole i, and pipe G G into the barrels; until at last the air in the receiver comes to be so much dilated, and its spring so far weak-ened, that it can no longer get through the valves; and then no more can be taken out. Hence, there is no such thing as making a perfect vacuum in the receiver; for the quantity of air taken out at any one stroke, will always be as the density thereof in the receiver: and therefore it is impossible to take it all out, because, supposing the receiver and barrels of equal capacity, there will be always as much left as was taken out at the last turn of the handle. There is a cock k below the pump-plate, which being turned, lets air into the receiver again; and then the receiver becomes loose, and may be taken off the plate. The barrels are fixed to the frame E e e by two screwnuts ff, which press down the top piece upon the barrels: and the hollow trunk H (in page 208) is covered by a box, G H (in page 207.) There is a glass tube Itn m m n open at both ends, and about 34 inches long; the upper end communicating with the hole in the pump-plate, and the lower end immersed in quicksilver at n in the vessel N. To this tube is fitted a wooden ruler m m, called the gage, which is divided into inches and parts of an inch, from the bottom at n (where it is even with the surface of the quicksilver) and continued up to the top, a little below I. to 30 or 31 inches. As the air is pumped out of the receiver M, it is likewise pumped out of the glass tube / m n, because that tube opens into the receiver through the pump-plate; and as the tube is gradually emptied of air, the quick 14. LECT. silver in the vessel N is forced up into the tube by the v_/ pressure of the atmosphere. And if the receive...