TRANSACTIONS OF WAGNER 

 74 



ETHER WAVES AND THE MESSAGES THEY BRING 



magnitude as the wave length of the waves to be studied. Rowland, of Johns 

 Hopkins University, ruled these gratings very successfully and they are much 

 used in the study of light. Now it occurred to Laue that if he had a grating 

 whose spacings were small enough, a spectrum of :r-rays could be produced, 

 provided they were, as he suspected, ether waves of very short wave length. 

 The hmit of physical possibility seemed to have been reached in the ruled 

 gratings, but it seemed to Laue that if the molecules of crystals are arranged 

 in planes, these planes might easily be so close together that their edges could 

 be used to diffract the a;-rays. Experiment proved that he was correct. 

 Using the experimental results he obtained, he computed the wave length of 



o 



the ::c-rays to be from i to lo Angstrom units. Tliis means that looo of them 

 would be about equal to the length of one light wave. In a few months after 

 these results were pubHshed Mr. W. L. Bragg, of Cambridge, England, an- 

 nounced that the x-rsLjs could be reflected from the face of a crystal. It is 

 found that crystal reflection differs from mirror reflection in that any given 

 wave length can be reflected only at certain angles. In this way the crystal 

 separates the various wave lengths in a beam of x-rays and arranges them in a 

 spectrum. Making use of this sort of x-ray spectroscope, Bragg found that 

 the various elements have characteristic x-ray spectra, just as they have char- 

 acteristic light spectra. The x-ray spectra of the various elements have been 

 studied and the elements classified according to them. The elements arrange 

 themselves in a certain order when thus classified, which is the same as their 

 order in the periodic system. Thus if the position of an element in the periodic 

 system be known, its radiations in the x-ray spectrum may be foretold, or, on 

 the other hand, if its x-ray spectrum be known, its position in the periodic 

 system has been determined. It has been stated that the x-rays of a given 

 wave length are reflected from crystals only at certain angles. These angles 

 are determined by the wave length and the distance between the planes of the 

 crystals. If any two of these are known, then the third can be determined by a 

 simple mathematical formula. Therefore, knowing the wave length of a beam 

 of x-rays and the angle at which it is reflected, it is possible to determine the 

 spacing of the planes in the crystal. 



The intensity of the reflected x-rays gives a clue as to whether the planes 

 are made up of light or of heavy atoms, for the heavier the atoms, the more 

 penetrating the reflected rayfe will be. Thus it is possible to show by the action 

 of the x-rays on crystals not only the spacing of the planes, but the arrange- 



