OBJECT: To measure the wavelength of light with a diffraction grating.
METHOD: A slit in an opaque screen, illuminated with a sodium flame or other source of bright line spectrum, is viewed through a diffraction grating held near the eye. With the rulings of the grating parallel to the slit, several orders of spectra are seen on either side of the slit. The various spectral images are located by means of a transverse scale mounted beside the slit. From the known value of the grating space and from the measured distances between the slit and the grating and between the slit and the successive spectra, the wavelength of light is calculated.
