Part 63

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?

3. (Pg. 136) In what particular do elastic, differ from non-elastic, fluids?

4. (Pg. 136) What is meant by the elasticity of air?

5. (Pg. 137) What is said respecting the weight of the atmosphere?

6. (Pg. 137) Why do we not feel the pressure of the air?

7. (Pg. 137) What would be the effect of relieving us from atmospheric pressure?

8. (Pg. 138) How may the weight of the air be shown by the aid of the air pump, and a piece of bladder?

9. (Pg. 138) How is this explained?

10. (Pg. 138) How may its elasticity be exhibited, by an apple, and by a bladder?

11. (Pg. 139) What is the absolute weight of a given column of atmospheric air, and how could its whole pressure upon the earth be ascertained?

12. (Pg. 139) How can the weight of a small bulk of air be found?

13. (Pg. 140) In ascertaining the weight of air, we take account of its temperature--Why?

14. (Pg. 140) How could you ascertain the specific gravity of air, and what would it be?

15. (Pg. 140) What are the essential parts of a barometer, as represented plate 14, fig. 3?

16. (Pg. 141) What sustains the mercury in the tube?

17. (Pg. 141) Of what use are the divisions in the upper part of the instrument?

18. (Pg. 141) To what height will the mercury rise, and what occasions this height to vary?

19. (Pg. 141) When is the mercury highest, in wet, or in dry weather?

20. (Pg. 141) What occasions the sensation of oppression, in damp weather?