Figure 2-2. Wave train passing along rope.

TM 9-258

(2) Electromagnetic spectrum. Heat and radio

colors of light. Practically all light is made up of many

colors, each color having its distinctive wavelength and

waves, light waves, ultraviolet and infrared rays, X-rays,

frequency. In as much as light of each color reacts in a

and cosmic rays are forms of radiant energy of different

slightly different manner when passed through different

wavelengths and frequencies. Together, they form what

mediums, provision must be made in optical elements to

is known as the electromagnetic spectrum (fig 2-3). The

control the action of light of various colors.

visible light portion of the electromagnetic spectrum

consists of wavelengths from 0.00038 to 0.00066

millimeter. The different wavelengths represent different

2-3