The light from the cradle will fall onto the sample and past rame, a mono chrome will serve to spread the light out by wavelength, to fall to the measuring machine.
Light from the source to fall On passing through the sample, a mono-chromate, which serves to spread out the various wavelengths of light to go off the detector.
The light from the cradle will fall. On the sample through the monochromator, which serves to spread out along the length of light wave, to fall also detector.