X rays and crystal structure . B and C were in reality close doublets, andthey gave the following values of the glancingangles of the rays (now five) of platinum : 9°28, 9°47, ii°i7, ii°28, and i3° estimated that these values were correct toone minute of arc. The crystal face was rock salt(100). They also measured the relative intensityof the general radiation in different parts of thespectrum. Moseley afterwards undertook a systematic in-vestigation of the spectra emitted by all the knownelements which could be brought under results are given in two papers published in\
X rays and crystal structure . B and C were in reality close doublets, andthey gave the following values of the glancingangles of the rays (now five) of platinum : 9°28, 9°47, ii°i7, ii°28, and i3° estimated that these values were correct toone minute of arc. The crystal face was rock salt(100). They also measured the relative intensityof the general radiation in different parts of thespectrum. Moseley afterwards undertook a systematic in-vestigation of the spectra emitted by all the knownelements which could be brought under results are given in two papers published in\^& Philosophical Magazine for December, 1913, andApril, 1914. They constitute a most remarkableand important contribution to the subject, * Second Solvay Congress (October, 1913). \ Phil. Mag. July, 1913. 76 X-RAY SPECTRA The experimental difficulties in the case of someof the substances examined were verv order to absorb the rays emitted by the variousanticathodes as little as possible, the X-ray bulb. Fig. 21. was provided with a thin aluminium window, throughwhich the rays passed on their way to the crystal,and thence to the photographic plate which regis-tered them. Some substances emitted rays so softthat goldbeaters skin had of necessity to be substi- X-RAY SPECTRA 77 tuted for the aluminium ; and, in addition, the wholespectroscope had to be enclosed in an evacuatedchamber, since the rays could not penetrate a fewcentimetres of air. Others, such as calcium, couldonly be submitted to the rays for very short periods,because they gave off gas which lowered thevacuum. Certain substances could only be examinedin alloy with others, or as chemical compounds, suchas oxides. A number of the photographic results obtained byMoseley are illustrated in Fig. 21, which is takenfrom his earlier paper. The figure displays thespectra of the characteristic radiations of certainmetals, ranging from calcium to zinc, the latterhaving been investigated as a constituent of
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