1. Why do clothes dry more quickly on a windy day than on a quiet day?

2. Does sprinkling the street on a hot day make the air cooler? If so, why?

3. In what part of the summer is the heat oppressive? Explain.

4. What becomes of the cloud of steam that escapes from the exhaust pipe of a power plant or a blowing locomotive whistle?

5. When does moisture gather on a water pipe? Why?

6. Why does the morning fog disappear usually before noon?

Fig. 60.   Siphon.

Fig. 60. - Siphon.

7. Why do we fan ourselves when we perspire?

8. Why must the bung of a barrel be removed in order to secure a proper flow of liquid from the faucet?

9. Why does high mountain climbing often cause pain and bleeding in the nose?

10. Small packages and folded papers are often transmitted in a carriage by air pressure through brass tubes called pneumatic dispatch tubes. An exhaust pump is attached to one end of the tube in which a tightly fitting carriage moves, and a compression pump to the other. If the air is half exhausted at one end and has twice its density at the other end, find the propelling force on the carriage if the tube is 4 in. in diameter.

11. Explain why it is impossible completely to exhaust a vessel of air by an air pump.

12. A pneumatic hammer, often called an "air gun," is used to drive rivets. Explain how it works.

13. Explain the care of a pneumatic hammer.

14. What is the practical value of a barometer? Explain the principle of a barometer.

15. Why is compressed air used in building a subway?

16. What advantage has compressed air over electricity in transmission of power?

17. Give some of the advantages of a pneumatic tire over a solid tire of the same size.

18. The general shape of boats and air-ships is usually made to conform to that of a fish. Why?

19. What is a fog?

20. What is a cloud?

21. Why is a bottle of hot water better than a hot stove cover for keeping your feet warm in bed?

22. Explain the principle of science underlying pneumatic machines.

23. Is it possible to measure gas pressure with the same gauges that are used to measure the pressure exerted by liquids?

24. How is air compressed? What is the commercial method of compressing air?