In a grating spectroscope, the prism is replaced by a grating - in its simplest form, a piece of glass on which a large number of parallel lines have been ruled. The more lines per inch, the better the grating: good gratings have as many as fifty thousand lines per inch. Light going through a grating will be dispersed into its various colors; the dispersion, however, in this case is not based on refraction as with the prism, but is rather due to interference between light rays that are transmitted in the spaces between the rulings.