A spectrograph has been designed and constructed by the author which has the following characteristics: (1) It can be used to solve nearly every problem which requires the use of a glass prism spectrograph and a number of problems for which a 21-foot grating is usually required. (2) In the violet it is equivalent to a 21-foot 15,000 lines to the inch grating in the second order with respect to resolving power and dispersion, and is free from ghosts. (3) The mounting is arranged in such a manner that more than 20 combinations are available by rather simple adjustments, giving a wide range of photographic speeds and dispersion. (Table I shows dispersion obtainable with different combinations of prisms and lenses.) (4) The spectrograph was constructed in our shop at a cost for optics and materials no greater than the cost of a small ready made single prism spectrograph.
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