10. Q. What is the highest velocity we can give a rifle ball? A. Two thousand feet a second.
11. Q. How long does it take light to travel from the sun to the earth? A. About eight minutes.
12. Q. What is light? A. The result of undulations in ether.
13. Q. What are the different effects we call color? A. They are simply various velocities of vibration.
14. Q. How does sunlight melt ice? A. In the middle, bottom, and top at once.
15. Q. What is the effect of dark heat on ice? A. It only melts the surface.
16. Q. What can you say of the passage of the heat of the sun and the heat of a furnace or stove through glass? A. Nearly all the heat of the sun goes through glass without hindrance; only a small portion of the heat of a furnace or stove goes through the same substance.
17. Q. If our air were as pervious to the heat of the earth as it is to the heat of the sun, how cold would the temperature of the earth become every night? A. Two hundred degrees below zero.
18. Q. What is said of worlds so distant as to receive from the sun only a thousandth part of the heat we enjoy? A. They may have atmospheres that retain it all.
19. Q. What is probable as to the temperature of Mars? A. It is probable that Mars, that receives but one-quarter as much heat as the earth, has a temperature as high as ours.
20. Q. What two radically different kinds of telescopes are made? A. The refracting telescope, and the reflecting telescope.
21. Q. Why is the refracting telescope so called? A. Because it is dependent on the refraction of light through glass lenses.
22. Q. Why is the reflecting telescope so called? A. Because it acts by reflecting the light from a concave mirror.
23. Q. What is the loss of light in the use of each kind of telescope? A. In passing through glass lenses it is about two-tenths. By reflection it is often one-half.
24. Q. In view of this peculiarity, among others, what is held as to the comparative quality of the two kinds of telescopes? A. That a twenty-six inch refractor is fully equal to any six-foot reflector.
25. Q. What is the weight of the Lord Rosse reflecting telescope? A. It has a metallic mirror weighing six tons, and a tube forty feet long, which, with its appurtenances, weighs seven tons more.