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"The radiation of light, or the intensity of light is inversely proportional to the square of the distance from the light source." —Croft 1917

Light Intensity

"The radiation of light, or the intensity of light is inversely proportional to the square of the distance…

"Another illustration of how luminous density varies inversely as the square of the distance." —Croft 1917

Light Intensity Versus Distance

"Another illustration of how luminous density varies inversely as the square of the distance." —Croft…

"A spectroscope is an instrument used ot produce a spectrum of the light form any source, and for its study." -Avery 1895

Spectroscope

"A spectroscope is an instrument used ot produce a spectrum of the light form any source, and for its…