364

Wirtz’s Pump.

[Book III.

»

of the coil is enlarged so as to form a scoop. When the machine, im-mersed in water as represented, is turned in the direction of the arrow,the water in the scoop, as the latter emerges, passes along the pipe driv-ing the air before it into G H, where it escapes. At the next revolutionboth air and water enter the scoop ; the water is driven along the tube asbefore, but is separated from the first portion by a column of air of nearlyequal length. By continuing the motion of the machine another portionof water and another of air will be introduced. The body of water in eachcoil will have both its ends horizontal, and the included air will be ofabout its natural density ; but as the diameters of the coils diminish to-wards the centre, the column of water which occupied a semicircle in theouter coil, will occupy more and more of the inner ones as they approachthe centre G, tili there will be a certain coil, of which it will occupy acomplete turn. Hence it will occupy more than the entire space withinthis coil, and consequently the water will run back over the top of thesucceeding coil, into the right hand side of the next one and push thewater within it backwards and raise the other end. As soon as the waterrises in the pipe G H, the escape of air is prevented when the scooptakes in its next quantity of water. Here, then, are two columns of wateracting against each other by hydrostatic pressure, and the intervening co-lumn of air. They must compress the air between them, and the waterand air columns will now be unequal. This will have a general tendencyto keep the whole water back and cause it to be higher on the left or ris-ing side of each coil, than on the other. The excess of height will be justsuch as produces the compression of the air between that and the preced-ing column of water. This will go on increasing as the water mounts inH. Now at whatever height the water in H may be, it is evident thatthe air in the small column next to it will always be compressed with theweight of the water in H—an equal force must therefore be exerted bythe water in the coils to Support the column in H. This force is the sumof all the differences between the elevation of the inner ends of the waterin each coil above the outer ends; and the height to which the water willrise in H will be just equal to this sum. Dr. Gregory observes that theprineiples on which the theory of this machine depends are confessedlyintricate ; but when judiciously constructed, it is very powerfül and effec-tive in its Operation. It has not been ascertained whether the helical orspiral form is best. Some of these machines were erected in Florence in1778. In 1784, one was made at Archangelsky, that raised a hogshead ofwater in a minute to an elevation of seventy-four feet, and through a pipeseven hundred and sixty feet long. See Gregory’s Mechanics, vol. ii.

It perhaps may facilitate an understanding of this curious machine, byremarking that the pressure exerted by the column of water in one side ofeach coil is proportioned to its length, and that this pressure is transmit-ted, through the column of air between them, to that of the next: the com-bined force of both is then made to act, by the revolution of the tubes,upon the third column, and so on, tili the accumulated force of them allis communicated to the water in H; and hence the elevation to whichwater can be thus raised, can never exceed the sum of the altitudes of theliquid columns in the coils.

END OP THE THIRD BOOK.