GENESIS OF THE ELEMENTS 161 



has stimulated speculative discussion to a degree previously 

 unknown. 



The ancient Greek philosophers might conceive systems of 

 the universe, based on ideas of motion or of matter, but as their 

 actual knowledge of nature was both limited to mere observation 

 and the results of observation often mistaken and always very 

 imperfect, their theories had no secure foundation. And even 

 down to the comparatively modern times of the eighteenth 

 century philosophical writers, Kant and Leibnitz and Laplace, 

 there was little to consolidate or support conclusions as to the 

 origin of matter and the cosmos. But through all the preceding 

 centuries it is remarkable how frequently the idea of an original 

 primal stuff, called by Aristotle v\rj, appears in the works of 

 philosophical writers. When, however, the definite discoveries 

 in chemistry made in the latter half of the eighteenth century, 

 and when the properties of hydrogen, especially its lightness, 

 became familiar it appeared to many chemists of that day as 

 though some of the speculations of the ancients were likely to 

 be fulfilled. 



The first, the crudest, and yet one of the most famous of the 

 modern forms of this idea is what appears in chemical literature 

 as " Prout's Hypothesis." William Prout was a physician and 

 chemist who lived from 1785 to 1850. He held the view that 

 the atomic weights of all the elements are integral multiples of 

 the atomic weight of hydrogen. But in the first place the atomic 

 weights in his day were but very inaccurately determined, and 

 the atomic weight of chlorine has always been found to approxi- 

 mate to 35 J when hydrogen is 1. He says in one of his essays : 

 " we may almost consider the Trpwrrj v\rj of the ancients to be 

 realised in hydrogen, an opinion, by the way, not altogether new." 



Some form of this hypothesis has doubtless hovered in the 

 minds of many chemists since that time, but in its original form 

 it has no basis in fact. 



The positive knowledge now derived from the discoveries of 

 J. J. Thomson as to the electric discharge in gases, and the work 

 of Rutherford, Soddy, Ramsay, and others on radio-active 

 substances seem to afford a justification for a reconsideration of 

 the subject. The world has also been influenced in many 

 directions by the use of ideas of evolution borrowed, in the first 

 instance, from the biological sciences though substantially 

 modified. So that in our own times speculation as to the origin 



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