the Corpuscular Hypothesis of the 7 and X Rays, 393 



Again, the absorption and scattering coefficients of liquids 

 and compounds for j3 rays have lately been the subject of 

 careful measurement by Schmidt* in Giessen, and by 

 Borodowsky f in Manchester, and the additive principle was 

 fully confirmed in this case also. 



A radiant entity, therefore, acts on one atom at a time; 

 and if its direction of motion is altered by a collision, the 

 alteration is determined by the mutual relations of the entity 

 and the atom alone. Neighbouring atoms have nothing to 

 do with it, and it is quite immaterial whether or no there is 

 a surface close by which separates one lot of atoms from 

 another. On the other hand, specular reflexion, such as the 

 reflexion of light in a mirror, depends on the conjoint action 

 of the atoms of the reflecting surface. It cannot be supposed, 

 therefore, that one part of the scattered /3 radiation examined 

 by McClelland consists of rays reflected like light; and this 

 being so, it is probable that the description of the remainder 

 as a true secondary is wrong also. In fact there is a much 

 more direct explanation of the whole effect. 



When an entity passes into an atom there is a chance of 

 deflexion through any given angle. Radii may be drawn 

 from the atom, each representing by its length the chance of 

 deflexion into the direction in which it is drawn. The 

 extremities of these radii will lie on a surface the form of 

 which will represent graphically the probable results of the 

 encounter ; and its form will vary with the atom, with the 

 nature of the entity, its speed, and so forth. As a rule the 

 lighter the atom the more eccentric is the oval surface. The 

 surface is one of revolution, the axis being the original line 

 of motion of the entity. A section through the axis will 

 therefore express all there is to express ; and such a section 

 may be called a " deflexion oval." It must be one of the 

 objects of experiment to determine the forms of the deflexion 

 ovals in all possible cases, for clearly, until we know the 

 probable results of an encounter between a given entity and 

 a given atom, we cannot calculate the result of the attempt 

 of an entity to pass -through a plate which is an aggregate 

 of many atoms ; in other words, we are not in a position to 

 calculate with safety the absorption coefficients or reflexion 

 coefficients of /3 rays. Although we do not yet know the 

 exact form of the oval when a /3 ray impinges on an atom, 

 we do know that it is far more eccentric for an aluminium 

 atom than for a lead one. The heavy atom is much more 

 likelv to swing round the electron than the light one : when 



* Phys. Zeit. xi. V . 262 (1910). 

 t Phil. Ma-. April 1910. 



