160 



THE NEW KNOWLEDGE. 



If these collections of corpuscles constituted atoms, the 

 mean of the atomic weights of the first and third would 

 be approximately the atomic weight of the middle one. 



Let us take another example: 



Again we find the same thing true. If the three col- 

 lections of corpuscles constituted three atoms they would 

 possess similar properties, and the mean of the atomic 

 weights of the first and third would be approximately the 

 atomic weight of the middle one. The two examples cited 

 are like those of sulphur, selenium and tellurium, and of 

 chlorine, bromine and iodine, page 21, and the curious 

 facts recited there find a simple rational explanation. 



THE PERIODIC LAW. 



' ' The properties of an element are a periodic function 

 of its atomic weight." 



This has been the great mystery of matter. If we ar- 

 range the elements of matter in the order of their atomic 

 weights, from lowest to highest, similar properties periodi- 

 cally recur. For example : With the element lithium cer- 

 tain properties are associated. The elements immediately 

 following lithium in the order of their atomic weights do 

 not possess these properties. They appear again, however, 

 when we come to sodium, then disappear until potassium 



