. The London, Edinburgh and Dublin philosophical magazine and journal of science. IN the preceding paper we have reported a preliminarystudy of the distribution of intensity among the spectraof different orders furnished by the echelette grating. Inthe present note we propose to show that these gratings giveus the highest resolving power that has yet been brought tobear upon the remote infra-red region of the spectrum. Theform of the intensity curve of the Reststrahleii reflectedfrom quartz, discovered by Rubens and Nichols, is shownin fig. 1, a, which is from a figure given by Coblentz. Thelo
. The London, Edinburgh and Dublin philosophical magazine and journal of science. IN the preceding paper we have reported a preliminarystudy of the distribution of intensity among the spectraof different orders furnished by the echelette grating. Inthe present note we propose to show that these gratings giveus the highest resolving power that has yet been brought tobear upon the remote infra-red region of the spectrum. Theform of the intensity curve of the Reststrahleii reflectedfrom quartz, discovered by Rubens and Nichols, is shownin fig. 1, a, which is from a figure given by Coblentz. Thelonger wave-length maximum is considerably higher thanthe short wave-length one, and the minimum between is veryshallow. A curve of practically the same form has beenobtained in all other investigations. In fig. 1, h is shown thecurve obtained with the echelette grating. The maxima are * Communicated by the Authors. Investigations with the JEchelette Grating. 899 practically of the same height, and the minimum betweenthem has an intensity of only about 1/3 that of the maxima i. in other words, it is very much deeper than when observedwith a rock-salt prism. The slit width wras only half a milli-metre, and the width of the bolometer strip was the type of curve was obtained with all of the gratingsThe maximum at 13, figured by Coblentz, who worked witha single reflexion only, did not appear in our work, as it waslost by the threefold reflexion which we employed. Thecurve obtained with the radiations of CO from the Bunsenflame is shown in fig. 2. There is distinct resolution of theband into a double band in the case of every curve addition to the strong band at 43 there are weakermaxima to the right and left. The curve figured wasobtained wTith grating No. 8. 900 Infra-Red Investigations with the Echelette Grating. The wave-lengths of the maxima of the bands for thequartz rays and the radiations from the flame have been very Fisr. 2.
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