By this device a very limited amount of light is permitted to pass from the object through the slit and lens to the prism and is there resolved into a spectrum, which is in effect a series of images of the slit in light of different colors, placed side by side so close as to make practically a continuous ribbon of light whose width is the length of each individual picture of the slit.
"A Text-Book of Astronomy"
George C. Comstock
Such a spectrum is shown in the central portion of Fig.
"A Text-Book of Astronomy"
George C. Comstock
A second principle is: The lines which appear in a spectrum are characteristic of the source from which the light came-e.
"A Text-Book of Astronomy"
George C. Comstock