ClipArt ETC
"The light to be studied is admitted through a narrow slit (A) in the end of a tube, in such a way that it will fall in parallel rays on a prism (C) with its edges parallel to the slit. When the beam emerges from the prism, the different colors are separated and the spectrum is viewed through lenses (E) placed at the end of another tube." -Brownlee 1907

Diagrammatic Representation of Spectroscope

"The light to be studied is admitted through a narrow slit (A) in the end of a tube, in such a way that…