the Corpuscular Hypothesis of the y and X Rays. 411 



cannot have much influence on the relative values of M for 

 the different linings. Mr. Porter finds that the figures are 

 indeed somewhat altered when the radium is moved about 

 into different positions, but the alterations are such as would 

 be expected from the variations in the quality of the 7 rays. 

 In some positions the 7 rays pass more obliquely through the 

 walls, and therefore through a greater thickness of lead, so 

 that they are so much the more hardened. 



When all allowances for error are made we still have a 

 set of figures which show with considerable accuracy the 

 relative values of kd in certain substances, and, since k is 

 practically the same for all of them, the relative values of d, 

 the range of the /3 particle. It may be well to point out 

 once more that this range does not give directly the power 

 of penetrating screens of different metals ; and indeed it 

 varies in the opposite direction. The power of penetration 

 depends also on the form of the deflexion oval which represents 

 the scattering effect. In the definition of the range, and in 

 the experiment which measures it, scatterings or reflexions, 

 or so-called secondary radiations, have no part at all. In 

 fact these experiments allow us to investigate separately one 

 of the three main subjects of measurement already referred 

 to, viz. the expenditure of energy along the track of the 

 /3 particle, since this must determine the length of the 

 track. 



In order to complete a proper set of investigations of the 

 ft particle phenomena, it is further necessary to find the form 

 of the deflexion oval in all cases. This may be done by 

 observing the scattering of the /3 rays in various directions 

 as they pass through very thin plates, since in such cases the 

 scatterings are due to one encounter with an atom in each 

 case, as Madsen has shown Qoc. cit.). The third subject of 

 measurement is the conversion of form : so far as we know 

 this is unimportant in the case of the /3 ray, but it is just 

 possible that an effect of this kind has been overlooked. 



Until satisfactory investigations have been made under 

 these heads, it is impossible to find true foundations for cal- 

 culation of the effects to be observed when sheets of material 

 are placed over a substance emitting ft rays, that is to say, of 

 the so-called absorption coefficients. For these coefficients 

 must necessarily vary in a complicated manner from material 

 to material and thickness to thickness, since they are involved 

 functions of the range and of the scattering. It is too much 

 to attempt a theory of the absorption of /3 rays until these 

 intermediate steps have been hewn into shape. H. W. 

 Schmidt has tried to fill up the gap by arguing back from a 



