420 Dr. Bar Ida and Mr. Sadler on Secondary 



Many proofs might be given of the same thing, but further 

 discussion of this point does not appear necessary. 



Of the results themselves there can be no question. [We 

 see from a note in ' Nature ' that Prof. Walter has verified 

 the observations made on the special penetrating power of the 

 secondary rays.] 



There are also so many experiments, the results of which 

 are so directly dependent on the structure of the atom and 

 which furnish numerical data (of varying degrees of accuracy) 

 pointing in independent ways to the same conclusion, that 

 we cannot but recognize the strength of the evidence that 

 the true atomic weight of nickel is approximately mid-way 

 between those of cobalt and copper. 



If the atomic weight of nickel were the usually accepted 

 value 587, we should from the first series of experiments be 

 compelled to conclude that the difference between atoms of 

 neighbouring atomic weights was in this case an exceptional 

 one ; in fact that the relation between atoms of nearly equal 

 weight was, so far as is known, in this case quite unique. 

 The fact that the position obtained by interpolation is between 

 cobalt and copper might be regarded as accidental. 



But the special power of the rays it emits of penetrating 

 certain substances shows that nickel behaves as a perfectly 

 normal substance with an atomic weight between those of 

 cobalt and copper. 



If the structure of the atom were an abnormal one, we 

 should expect the behaviour of the atom to be like that of 

 an atom of one weight in one property and that of another 

 weight in another property. To be more precise, if we con- 

 sidered the possibility of the accepted atomic weight of nickel 

 being correct, we should have to conclude that its constitution 

 is an irregular one, but that it behaves in all the ways dis- 

 cussed as an imaginary atom, built up in a perfectly regular 

 way, and possessing an atomic weight of about 61*4, whereas 

 we should have expected inconsistencies in the values indi- 

 cated by different experiments. 



We cannot conceive of two different systems — a real and 

 an imaginary one — possessing so many properties, identical 

 in quantity as well as quality. For these properties — 

 the. definite power of absorbing #-rays, of emitting under 

 a?- ray stimulus corpuscular radiation of definite ionizing 

 power, of emitting under a?-ray stimulus secondary /p-rays of 

 definite properties (the general and special properties referred 

 to) and the property of being susceptible to a definite extent 

 to #-rays of various penetrating powers — are evidently 

 dependent on the number, arrangement, and velocity of the 



