Hilger wavelength spectrometer with camera, c 1919.
© Science Museum / Science & Society Picture Library
A wavelength spectrometer made by Adam Hilger, London, which was used at New Cros Hospital in Wolverhampton. The instrument measures the angle light is refracted (bent) after pasing through a prism. Unlike a simple spectroscope, where the wavelength of light is determined by comparison with a known light source, the spectrometer only measures the angle of deflection. Like its counterpart, it is used to examine the chemical nature of material that has been vaporised in a hot flame. In operation, light enters through the slit on the left-hand-side tube, is deflected by the prism and is recorded using the camera on the same side. The angular displacement of the spectrum is determined by measuring the photographic plate.