A Recording Spectrograph for the Far Infra-Red

Abstract

This spectrograph records upon sheets of photographic paper 20×30 inches in size, spectra lying in the range between 18μ and 200μ. Of this range, 9μ may be spread over a single record, or as much as 100μ may be covered, depending upon the gratings and the adjustments used. The spectrograph is a vacuum instrument of high resolving power, being capable of separating sharp lines somewhat closer than 0.5 cm⁻¹ apart. Detailed drawings of its construction together with several records are shown and described. The recorded galvanometer deflections are usually adjusted to lie between 100 and 300 mm.