Q. What is ether?
A. A very subtile fluid, which pervades and surrounds every thing we see.
Q. Mention a simple experiment to prove that light is produced by rapid motion.
A. When a fiddle-string is jerked suddenly, its rapid vibration produces a grey light; and when a carriage wheel revolves very quickly, it sends forth a similar light.
Q. Does heat always produce light?
A. No: the heat of a stack of hay, or reeking dunghill, though very great, is not sufficient to produce light.
Q. Why is a yellow flame brighter than a red hot coal?
A. Because yellow rays always produce the greatest amount of light; though red rays produce the greatest amount of heat.
Q. Why is the light of a fire more intense sometimes than at others?