The water, is thus first raised in the pump, and then forced into the pipe, by the alternate ascending, and descending motion of the piston, after a few strokes of the handle to fill the pipe, from whence the water issues at the spout.
Emily. Does not the air pump, which you used in the experiments, on pneumatics, operate upon the same principles as the sucking pump?
Mrs. B. Exactly. The air pump which I used ([plate 1, fig. 2],) has two hollow, brass cylinders, called barrels, which are made perfectly true. In each of those barrels, there is a piston; these are worked up, and down, by the same handle; the pistons, are furnished with valves, opening upwards, like those of the common pump: there are valves also, placed at the lower part of each barrel, which open upwards; there are therefore two pumps, united to produce the same effect: two tubes, connect these barrels with the plate, upon which I placed the receivers, which were to be exhausted.
Emily. I now understand how the air pump acts; the receiver contains air, which is exhausted, just as it is by the common pump, before the water begins to rise.
Mrs. B. Having explained the mechanical properties of air, I think it is now time to conclude our lesson. When next we meet, I shall give you some account of wind, and of sound, which will terminate our observations on elastic fluids.
Caroline. And I shall run into the garden, to have the pleasure of pumping, now that I understand the construction of a pump.
Mrs. B. And, to-morrow, I hope you will be able to tell me, whether it is a forcing, or a common lifting pump.
Questions
1.(Pg. [136]) Into what two kinds are fluids divided?
2.(Pg. [136]) There are different kinds of elastic fluids, in what properties are they alike, and in what do they differ?