Light

Light is an interesting part of life. People through the centuries have had different ideas of how light works. Ancient Egyptians thought that light rays came from the eyes. How wrong they were. Light has the properties of both a wave and a particle. For many years scientists have been trying to pin light into one category, unsuccessfully. (Now this subject is a little harder than the last one so you'll be expected to know most of the words here. But, you can't know everything.) So, lets define some necessary terms.

Propagation- movement of a wave through a medium

Wave- a periodic disturbance that propagates (moves) through a medium or space.

Medium- any region through which a wave propagates.

In general, energy can be propagated either by particles of matter or by wave disturbances traveling from one place to another. A window pane may be shattered by a baseball thrown through it, or by the shock wave of a distant explosion.

There were arguments supporting both a particle(a.k.a. corpuscular) theory and the wave theory. On the side of the particle theory was the renowned Father of Physics, Sir Isaac Newton and French mathematical physicist and astronomer, Laplace. The wave theory was supported by Christian Huygens (that's pronounced hi-ganz), Dutch mathematician, physicist, and astronomer. He in turn was supported by Robert Hooke of England.

Because both theories sounded good, made sense, and were supported by such distinguished men, scientists were hard pressed to fit light into one classification. If you want to see some of the arguments for the two theories just click one of these:

Corpuscular Theory
Wave Theory