10 president's address 



The modern conception of the elements was much strengthened by 

 Dalton's revival of the Greek hypothesis of the atomic constitution of 

 matter, and the assigning to each atom a definite weight. This 

 momentous step for the progress of chemistry was taken in 1803 ; the 

 first account of the theory was given to the public with Dalton's consent 

 in the third edition of Thomas Thomson's ' System of Chemistry ' in 

 1807; it was subsequently elaborated in the first volume of Dalton's 

 own ' System of Chemical Philosophy, ' published in 1808. The notion 

 that compounds consisted of aggregations of atoms of elements, united 

 in definite or multiple proportions, familiarised the world with the 

 conception of elements as the bricks of which the Universe is built. 

 Yet the more daring spirits of that day were not without hope that the 

 elements themselves might prove decomposable. Davy, indeed, went 

 so far as to write in 1811 : ' It is the duty of the chemist to be bold 

 in pursuit ; he must recollect how contrary knowledge is to what appears 

 to be experience. ... To inquire whether the elements be capable of 

 being composed and decomposed is a grand object of true philosophy.' 

 And Faraday, his great pupil and successor, at a later date, 1815, was 

 not behind Davy in his aspirations, when he wrote : ' To decompose 

 the metals, to re-form them, and to realise the once absurd notion of 

 transformation — these are the problems now given to the chemist for 

 solution.' 



Indeed, the ancient idea of the unitary nature of matter was in 

 those days held to be highly probable. For attempts were soon made 

 to demonstrate that the atomic weights were themselves multiples of 

 that of one of the elements. At first the suggestion was that oxygen was 

 the common basis; and later, when this supposition turned out to be 

 untenable, the claims of hydrogen were brought forward by Prout. 

 The hypothesis was revived in 1842 when Liebig and Eedtenbacher, and 

 subsequently Dumas, carried out a revision of the atomic weights of 

 some of the commoner elements, and showed that Berzelius was in 

 error in attributing to carbon the atomic weight 12.25, instead of 12.00. 

 Of recent years a great advance in the accuracy of the determinations 

 of atomic weights has been made, chiefly owing to the work of Eichards 

 and his pupils, of Gray, and of Guye and his collaborators, and every 

 year an international committee publishes a table in which the most 

 probable numbers are given on the basis of the atomic weight of oxygen 

 being taken as sixteen. In the table for 1911, of eighty-one elements 

 no fewer than forty-three have recorded atomic weights within one- 

 tenth of a unit above or below an integral number. My mathematical 

 colleague, Karl Pearson, assures me that the probability against such 

 ft condition being fortuitous is 20,000 millions to one. 



The relation between the elements has, however, been approached 

 from another point of view. After some preliminary suggestions by 



