A large Wadsworth grating spectrometer designed primarily for photoelectric recording is described. Important features of the instrument are an arrangement which permits any wavelength interval up to the full range of the spectrometer to be scanned in one continuous operation and a wavelength scale which is linear over the entire spectral range (2000 to 14,000A). The linear scale results in part from scanning the spectrum on the grating normal, a condition which leads also to minimum aberrations in the spectral image. Provision is made for indicating on the spectrum record reference marks which denote equal increments of wavelength. Multiplier photo-tubes, operating at liquid nitrogen temperature, are used in the photoelectric recording system. The scanning slit (or photographic plate) is maintained automatically on the focal curve by a simple focusing device. The spectrometer is fully adaptable to photographic work and may be converted from photoelectric recording to photographic recording (or vice versa) in about five minutes.
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