On the mercury green line λ = 5461 resolved by glass and quartz lummer plates and on its zeeman constituents

Abstract

Numerous investigators have studied the structure of some of the finer line in the mercury arc, and other spectra, with ruled gratings, échelon spectroscopes, and Lummer plates; but up to the present when Lummer plates and échelons were used these were invariably made of glass. A short time ago a Lummer plate of crystal quartz was made for the Physical Laboratory at Toronto by the Adam Hilger Company, for the investigation of the structure of some of the finer lines in ultra-violet spectra; but before proceeding to use it for this purpose some measurements were made with it, and with two Lummer plates made of glass, on the wave-lengths of the satellites of the mercury green line λ = 5461 Å. U. At the same time a precise method of measuring up the photographic fringe patterns produced by Lummer plated has been developed in which the geometrically central line of the double fringe pattern is taken as the line of reference in the measurements. This exact formula permits of the use of the fringes that emerge from the plate at nearly grazing direction, for which the dispersion is the greatest. The following paper contains an account of the investigation and includes the values of the wave-lengths of the satellites of the green line as deduced by the application of the method to which reference has just been made. The quartz Lummer plate, it may be added, was cut with the axis of the crystal parallel to the plane refracting surfaces and perpendicular to the length of the plate. The source of the light used in the investigation was one or other of a number of ordinary Cooper-Hewitt mercury-arc lamps. The light was passed through the collimator tube of a spectroscope and then into the plate in the usual manner.