ABSTRACT
The types of carbon arcs suitable for experiments in optics have a vertical carbon rod of 0.5 cm diameter and a horizontal one of 0.7 cm diameter. The arc is lighted by bringing the two carbon rods into contact and then separating them immediately by a distance of about one centimeter. Optical filters are used to transmit spectral bands of known width in a continuous spectrum or to isolate certain radiations in a line spectrum. Filters for isolating the visible lines of mercury, anti-caloric filters, semi-reflecting mirrors and cold mirrors are available commercially. The light radiation, the spectrum of which we want to obtain, is dispersed by a prism or a grating. The superimposition of different radiations of the spectrum gives the sensation of white.
