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THE PRESIDENTIAL ADDRESS. 3 
the fundamental problem, while the development of new methods and 
appliances required for technical purposes often provides the investi- 
gator with means of attacking still more difficult questions. This 
important reaction between pure and applied science can be illustrated 
in many branches of knowledge. It is particularly manifest in the 
industrial development of X-ray radiography for therapeutic and indus- 
trial purposes, where the development on a large scale of special X-ray 
tubes and improved methods of excitation has given the physicist much 
more efficient tools to carry out his researches on the nature of the rays 
themselves and on the structure of the atom. In this age no one can 
draw any sharp line of distinction between the importance of so-called 
pure and applied research. Both are equally essential to progress, 
and we cannot but recognise that without flourishing schools of research 
on fundamental matters in our universities and scientific institutions 
technical research must tend to wither. Fortunately there is little 
need to labour this point at the moment, for the importance of a training 
in pure research has been generally recognised. The Department of 
Scientific and Industrial Research has made a generous provision of 
grants to train qualified young men of promise in research methods in 
our scientific institutions, and has aided special fundamental researches 
which are clearly beyond the capacity of a laboratory to finance from 
its own funds. Those who have the responsibility of administering the 
grants in aid of research both for pure and applied science will need all 
their wisdom and experience to make a wise allocation of funds to 
secure the maximum of results for the minimum of expenditure. It 
is fatally easy to spend much money in a direct frontal attack on some 
technical problem of importance when the solution may depend on 
some addition to knowledge which can be gained in some other field of 
scientific inquiry possibly at a trifling cost. It is not in any sense my 
purpose to criticise those bodies which administer funds for fostering 
pure and applied research, but to emphasise how difficult it is to strike 
the correct balance between the expenditure on pure and applied science 
in order to achieve the best results in the long run. 
It is my intention this evening to refer very briefly to some of the 
main features of that great advance in knowledge of the nature of 
electricity and matter which is one of the salient features of the interval 
since the last meeting of this Association in Liverpool. 
In order to view the extensive territory which has been conquered 
by science in this interval, it is desirable to give a brief summary of 
the state of knowledge of the constitution of matter at the beginning 
of this epoch. Ever since its announcement by Dalton the atomic 
theory has steadily gained ground, and formed the philosophic basis 
for the explanation of the facts of chemical combination. In the early 
stages of its application to physics and chemistry it was unnecessary 
