This is a very bright spectral source which shows bright lines as well as a continuous spectrum. Light from the superpressure mercury source passes through a condenser lens and iris and is focused onto a slit by a 10 cm focal length cylindrical convex lens. A 20 cm focal length spherical convex lens focuses the slit onto a distant screen, with the flint glass prism placed in the light just after the lens. Note that the two violet rays at the left of the spectrum are actually ultraviolet, but can be seen because of fluorescent materials in the white paper used as the photography backdrop.
DO NOT REMOVE the condenser lens, because of possible UV radiation hazard.