i68 POPULAR SCIENCE MONTHLY. 



determinations, the more probable it seemed that in reality cobalt, and 

 not nickel, as demanded by theory, has the greater weight. The whole 

 subject has been very carefully investigated in the last few years by 

 Prof. Theodore W. Eichards at Harvard University, and there seems 

 now to be no doubt but that Nature has unexpectedly and inexplicably 

 reversed the position of these elements. 



Another instance that seems to be of the same nature is that as far 

 as the most accurate determinations go, tellurium has an atomic weight 

 greater than that of iodin, instead of less. At present it is impossible 

 to explain these abnormalities, but they assure us of the possibility that 

 argon may have a higher atomic weight than potassium, and yet belong 

 to the eighth group. 



What now is the present position of the philosophy of matter from 

 the light thrown upon it by the Periodic Law? In the first place, draw- 

 ing our deduction from the marvelously accurate determinations of. 

 the relative weights of the atoms of the different elements, to which 

 chemists have been incited by the Periodic Law, it may be considered 

 as absolutely settled that the elements are not groups of hydrogen 

 atoms, nor are they composed of half or quarter hydrogen atoms. As 

 enunciated by Prout, the hypothesis which goes by his name may be 

 considered as finally proved untenable; the atomic weights are not 

 multiples of the weight of the hydrogen atom, nor any simple fraction 

 thereof. But while this is the case, it is perfectly clear from the 

 Periodic Law that the properties of an atom are a periodic function of 

 its atomic weight. It would seem that this can be true only if the 

 material of which all atoms are made is the same. This does not 

 necessarily mean that there is but one kind of matter, and that all 

 atoms are merely different quantities of this 'urstoff.' There may be 

 several kinds of matter, and different kinds of atoms may represent 

 varying proportions of a few constituents. 



There have been many attempts to reduce the Periodic Law to 

 mathematics, in order to find a numerical value for the function which 

 expresses the relation between atomic weight and an element's place 

 in the series. Such efforts have been thus far wholly unsuccessful. It 

 is by no means impossible that such relations will be found in the 

 future, but at present the atomic weights of comparatively few ele- 

 ments have been determined with great accuracy. When this work 

 has been extended to a greater number of elements, and when the 

 position of the rare elements and of the inert atmospheric gases haa 

 been definitely settled, we may hope for more light upon the principles 

 underlying the Periodic Law. 



At present this law occupies much the same position as two other 

 great generalizations of natural science. The fact of gravitation was 

 long ago discovered. The laws by which it acts are well known, and 



