30 SECTIONAL ADDRESSES. 
minds of the most imaginative of us. The ideas which revolutionise 
Science are just those of which our theories give no indications. Theories 
are the very life-blood of Physics, most of the researches in our laboratories 
originate in an attempt to test a theory; theory, however, may be 
injurious if it makes us concentrate our attention exclusively on the 
particular problem it suggested, and to treat as an annoyance, to be 
avoided by a change in method, any anomaly in the experiment which 
interferes with our progress to the goal; the anomaly may be the outcrop 
of a vein rich in new phenomena. After Réntgen had discovered X-rays, 
another physicist who had been working with somewhat similar apparatus 
said that he had noticed that any photographic plates near his tube got 
fogged and spoiled; he moved his plates further away and left it at that. 
The discovery of argon by Lord Rayleigh arose from some vexatious 
discrepancies in a series of weighings. 
I do not think that there is any danger of the supply of new physical 
phenomena being exhausted and of Physicists joining the ranks of the 
unemployed. Rather do I believe that as each successive Centenary 
comes round the President of Section A will be able to say that the growth 
of Physics in the century which has just passed is comparable with that 
in any of its predecessors. 
