A Large Recording Spectrograph for the Infra-Red to 15μ

Heretofore the rocksalt prism spectrograph has been used mainly as a ``survey instrument'' to locate regions of spectral absorption over a wide wave-length range. When a resolving power equivalent to the theoretical limit of a large prism (varying from 1 cm−1 at 6μ to 0.3 cm−1 at 15μ) was obtained with the present instrument its scope of usefulness was found to be greatly increased. The improvements in detail necessary to achieve this practical balance between prism size, aperture and sensitivity of detection are described.