9. Q. At what velocity does light travel? A. One hundred and eighty-five thousand miles per second.
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.