( 716 ) 



or changes its direction considerably l ) in a centre of' exceedingly 

 strong electromagnetic action ; in the great majority of cases it will, 

 by the abundance of* vacant space in the interior of the atom 2 ), fly 

 across it without experiencing a considerable decrease of velocity. 



In this way the greater part of the electrons will pierce thousands 

 or tens of thousands of atoms before being stopped, and we find 

 easily explained the great penetrating power of the cathode-rays, 

 which may still in appreciable quantity pass through a layer of 

 aluminium 10 ft 3 ) thick or a layer of atmospheric air, some cm thick 4 ). 



If we consider the values given by the diffraction-experiments 

 for the order of magnitude of the thickness of R. -waves as correct, 

 it follows from Wii.n's experiments — apart from a possible 

 catalytic action of the R.-rays — that the radiation of the cathode-ray 

 corpuscles, by the simple fact of their stoppage, could account only for 



something like or - of the whole energy of the R.-rays. Conse- 



b 20 100 bj j 



quently for by far the greater part this energy must, if Lenard's 

 views may be accepted, have a different origin. What this can be, 

 is obvious. The atoms namely will by no means remain undisturbed 

 during the sudden passage of an electron. Themselves probably con- 

 sisting of negative and positive corpuscles, they will see their electro- 

 magnetic tields during the passage altogether altered and at the same 

 time will no doubt send out a pulse or wave of disturbance 5 ) into 

 the surrounding ether. About the character or shape of these pulses, 

 which moreover may vary from one case to an other, we can, 

 without making any more definite assumptions as to the structure 

 of the atom, say little; but there is one important point, in which 

 all these pulses will be to a certain degree similar, viz. their duration. 



1 ) Together with the expulsion of electrons originally belonging to the atom, 

 which will often occur at the same time, these changes of direction could very 

 well account for the diffusion of the cathode-rays according to Lenard. 



2 ) Lenard calculates (Dfudes Ann. d. Ph. 12, p. 739, 1903) that only 10-9 of 

 the volume of an atom is occupied by the "dynamids", of which he considers it 

 to consist. 



3) Lenard. Wied. Ann. 51, p. 233, 1894. 

 l ) Id., Ibid., p. 252. 



5 ) Lenard expresses himself ('Ueber Kathodenstrahlen", Nobel-vorlesung, p. 37, 

 Leipzig 1906) as follows : "Das durchquerende Strahlenquant" — the electron — 

 "wird vermöge der abstossenden Krafte, welche es auf die anderen, dem Atom 

 eigenen, negativen Quanten ausübt, eine gewaltige Störung innerhalb des Atoms 

 hervorbringen können", and then continues thus: "und als Folge dieser Störung 

 kann ein dem Atom gehüriges Quant aus ihm hinausgeschleudert werden (sekundare 

 Kathodenstrahlung)"; but he does not speak of a radiation emitted by the atom. 



