III. Description of a train of eleven sulphide-of-carbon prisms arranged for spectrum analysis

Abstract

The principles which should regulate the construction of a battery of prisms have been alluded to in the description of the large spectroscope now at Kew Observatory, which has a train of nine dense glass prisms with refracting angles of 45°. While for purposes of exactitude, such as mapping out the solar spec­trum, flint glass stands unrivalled; yet when the greatest amount of dis­persion is the desideratum, prisms filled with bisulphide of carbon present obvious advantages, on account of the enormous dispersive power of that liquid—the difference of its indices of refraction for extreme rays being, according to Sir David Brewster, as 0·077 against 0·026 for flint glass.