Man's physical universe

xanabras

LIGHT IS A FORM OF RADIANT ENERGY 389

produced provided the necessary data for his calculations. These light

waves were found to be very short, about 1/50,000 inch.

Recently Newton's corpuscular theory has found favor again,

although the modern concept of energy packets, called quanta, diiifers

considerably from Newton's corpuscles. Rapidly moving electrons

and protons have been shown to exhibit some of the properties of waves

and to produce interference patterns, while photons, or light corpuscles,

are accepted as realities today. At present, therefore, light is considered

to be both wavelike and corpuscular in nature, but the wave metaphor

and the particle metaphor are used in quite different contexts. Roughly

speaking, when we want to know or account for where a beam of light

goes, we pretend it is a wave motion ; whereas when we want to account

for what it does when it gets there we pretend it is somehow corpuscular.

Of course this dualism is unsatisfactory — it constitutes a problem

to be solved.

Radiant-energy units are now generally referred to as photons. The

amount of energy of photons varies with the frequency of the radiations.

Photons of red light contain less energy than those of violet. As

the frequencies become greater, the energy of the photons becomes

greater. Thus, for X rays the photons are so large that they show

atomic characteristics. A. H. Compton of Chicago has shown that

X rays falling on electrons scattered as if they consisted of material

particles.

How Waves Transfer Energy.

Huygens proposed the existence of a hypothetical medium for the

waves to travel in, which he called "ether." Ether is a hypothetical

medium that is supposed to occupy otherwise unoccupied space. ^ The

concept of ether is useful, but it must be kept in mind that there is no

experimental evidence for its existence. It is not known how light

really travels, but an exact account of its path can be given if it is

regarded as a train of waves.

Light waves are supposed to be propagated through the ether in a

manner somewhat analogous to the propagation of water waves. If a

stone is thrown into a pool of water, the surface will be depressed

momentarily, and a series of circular waves will spread from that point.

Finally the waves reach the shore and move small objects. The energy

used to do work on these objects is transmitted by the waves from the

stone. Now, if stones are thrown into a pool at the same rate in rapid

succession, the waves formed will move at the same rate, but the

distance from crest to crest and from trough to trough will depend upon

' Eddington defines ether as follows: "Ether is the subject of the verb, to undulate."

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