A new design for a stellar spectrograph which embodies lightness in weight with high rigidity is described. The instrument is composed of three parts: the spectrograph proper, the inner case or “rigidity box,” and the constant temperature case. The spectrograph proper is a light weight instrument which may be removed easily from the mounting and used as a laboratory instrument if desired. The “rigidity box” is the member which forms the main support for the spectrograph. The method of mounting is such that the spectrograph proper has a small degree of freedom which minimizes the possibility of small stresses being transmitted to it from mechanical or thermal causes. The constant temperature case is an easily removed cover which provides a second constant temperature air space about the spectrograph and with a triple fan system provides an efficient temperature control for the instrument. The spectrograph is equipped with a slit which eliminates troubles arising from lack of parallelism of the jaws, shifting zero and back-lash. The slit may be opened rapidly to maximum width for intensity calibration without loosing a predetermined slit width. Curves showing the performance of the thermal-control system are given, as well as photographs of the mechanical parts.
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