Our eyes are capable of seeing only a narrow spectrum of light.
The dark lines of the spectrum of sunlight, earliest noted by Dr W.
The spark spectrum of gold has been mapped by A.
Mention may be made of the absorption spectrum of benzene.
Let AoBo be a plane wave-surface of the light before it falls upon the prisms, AB the corresponding wave-surface for a particular part of the spectrum after the light has passed the prisms, or after it has passed the eye-piece of the observing telescope.