aS” ~ 
THE PRESIDENTIAL ADDRESS. 21 
require to know as many atomic weights as there are isotopes, and the 
chemist may well be appalled at such a prospect. All sorts of difficulties 
start up to affright him, such as the present impossibility of isolating 
isotopes in a state of individuality, their possible instability, and the in- 
ability of his quantitative methods to establish accurately the relatively 
small differences to be anticipated. All this would seem to make for 
complexity. On the other hand, it may eventually tend towards simpli- 
fication, If, with the aid of the physicist we can unravel the nature and 
configuration of the atom of any particular element, determine the 
number and relative arrangement of the constituent protons and elec- 
trons, it may be possible to arrive at the atomic weight by simple 
calculation, on the assumption that the integer rule is mathematically 
yalid. This, however, is almost certainly not the case, owing to the 
influence of ‘ packing.’ The little differences, in fact, may make all the 
difference. The case is analogous to that of the so-called gaseous laws 
in which the departures from their mathematical expression have been 
the means of elucidating the physical constitution of the gases and of 
throwing light upon such variations in their behaviour as have been 
observed to occur. There would appear, therefore, ample scope for the 
chemist in determining with the highest attainable accuracy the de- 
partures from the whole-number rule, since it is evident that much 
depends upon their exact extent. 
These considerations have already engaged the attention of chemists. 
For some years past, a small International Committee, originally 
appointed in 1903, has made and published an annual report in which 
it has noted such determinations of atomic weight as have been 
made during the year preceding each report, and it has from time 
to time made suggestions for the amendment of the Tables of Atomic 
Weights, published in text-books and chemical journals, and in use in 
chemical laboratories. In view of recent developments, the time has 
now arrived when the work of this International Committee must be 
reorganised and its aims and functions extended. The mode in which 
this should be done has been discussed at the meeting in Brussels, in 
June last, of the International Union of Chemistry Pure and Applied, 
and has resulted in strengthening the constitution of the Committee and 
in a wide extension of its scope. 
The crisis through which we have recently passed has had a pro- 
found effect upon the world. The spectacle of the most cultured and 
most highly developed peoples on this earth, armed with every offensive 
appliance which science and the inventive skill and ingenuity of men 
could suggest, in the throes of a death struggle must have made the 
angels weep. That dreadful harvest of death is past, but the aftermath 
remains. Some of it is evil, and the evil will persist for, it may be 
