A New Design of Precision X-Ray Spectrometer
spectrometer is especially designed to make use of the "Method of Displacement," already published, for the determination of X-ray wave-lengths. This method is briefly described. Description of the Spectrometer.-A detailed description of the spectrometer with a plan and side elevation are given. Adjustments.-The processes involved in the adjustment of the spectrometer for precision measurements on X-ray wave-lengths are explained in detail. Verification of the Fundamental Assumption on which
... umption on which the "Method of Displacement" is Based.-The method requires that a portion of the length of a beam of X-rays, after reflection, shall be of constant width. The possibility of this has been previously demonstrated on theoretical grounds. An exploration of the reflected beam for the ax line of the K series of silver has been made and the results are found to agree with theory. PRINCIPLE. A METHOD has been devised for measuring wave-lengths in the ^~^ X-ray region of the spectrum, by Professor H. S. Uhler, 1 which promises to eliminate many of the errors involved in earlier methods. The method requires the use of two slits of equal width between the source of rays and the crystal and a means of displacing the photographic plate in a straight line parallel to the line of collimation of the spectrometer, the plate undergoing no rotation during the displacement. The glancing angle of reflection at the crystal is then determined solely by the distance apart of the spectral lines, taken on both sides of the direct image of the slits in the two positions of the plate, and the distance through which the plate has been displaced. These distances can both be measured on the same comparator, thus making the determination of glancing angles depend solely on two linear measurements in the same units. This method of displacement for determining glancing angles was given a preliminary trial by Uhler and myself 2 in our work on the K series of gallium. The spectrometer we then used had not been constructed originally for this method, but the results obtained with the remodelled apparatus encouraged us to believe that with a properly designed instrument the method would be capable of great precision.