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.
26. Q. What is a spectrum? A. A collection of the colors which are
dispersed by a prism from any given light.
27. Q. If the light is sunlight what is the spectrum called? A. A solar
spectrum.