2 80 Mr. W. Sutherland on 



rays are absorbed, and most powerfully where the absorption 

 is most powerful : this corresponds with all the facts as to 

 the place of origin of Ronigen rays. 



As to what must be the order of magnitude of the length 

 of the waves in the aether produced by the internal vibrations 

 of the electrons, we can form no a priori estimate, but under 

 the circumstances we are at liberty to assume that, like the 

 size of the electron, it is small compared to that of atoms, and 

 small also compared to molecular interspaces. We shall 

 then have to do with systems of waves, which, when they 

 fall on a body, can travel freely in the molecular interspaces, 

 but are liable to absorption near the surfaces of molecules. 

 The propagation of such a system of waves would take place 

 almost entirely in the a?ther of the interspaces, as sound travels 

 through a loose pile of stones mostly by the air-spaces ; the 

 molecules cause absorption, but do not act as if they loaded 

 the sether. Therefore when our system of waves enters a 

 body it experiences no refraction. As to reflexion at the first 

 layer of molecules which it encounters, we must remember 

 that our wave-length is small compared to the radius of a 

 molecule or atom, and that therefore in studying reflexion it 

 suffices to study that from a single molecule ; whereas, with 

 ordinary light, where the wave-length is large compared to 

 atomic radius, we have to take the effect of a large number 

 of contiguous molecules, if we are to reason out results com- 

 parable with those observed in ordinary reflexion. Now the 

 reflexion of our small waves from a single molecule will be of 

 the same nature as reflexion from a sphere, and will be similar 

 to diffuse scattering, a good deal of the scattering being 

 towards the neighbouring interstices. Thus the attempt to 

 reflect these waves from a material plane surface will be 

 similar to that of attempting to reflect ordinary light from a 

 large number of smooth spheres whose centres lie in a plane. 

 If we take the average effect of a large number of molecules 

 whose centres are by no means in a plane, as must be the 

 case with our best reflecting surfaces, we see that a diffuse 

 scattering of our small waves must take the place of re- 

 flexion, and this is the experimental result with the Rontgen 

 rays. 



Any polarization that our system of waves might possess 

 could not be detected by the ordinar}' optical appliances, 

 because these depend on actions exercised by the molecules 

 on the vibrations of light, whereas, as our small waves travel 

 by the interstices between the molecules, their character is 

 not controlled to any appreciable extent by the molecular 

 structure. This result also agrees with the experimental one 



