ELECTRICAL STRUCTURE OF MATTER RUTHERFORD 163 



vides the investigator 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 radio- 

 graphy for therapeutic and industrial purposes, where the develop- 

 ment 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 lino 

 of distinction between the importance of so-called pure and applied 

 research. Both are equally essential to progress, and Ave can not 

 but recognize that without flourishing schools of research on funda- 

 mental matters in our universities and scientific institutions technical 

 research must tend to wither. Fortunately there is little need to 

 labor this j)oint at the moment, for the importance of a training in 

 pure research has been generallj'^ recognized. 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 funda- 

 mental researches which are clearly beyond the capacity of a labora- 

 tory to finance from its own funds. Those who have the responsi- 

 bility 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 direct frontal attack on some technical problem of im- 

 portance when the solution may depend on some addition to know- 

 ledge 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 

 criticize those bodies w^hich administer funds for fostering pure and 

 applied research, but to emphasize 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 be- 

 ginning of this epoch. Ever since its announcement by Dalton the 

 atomic theory has steadily gained ground, and formed the philo- 

 sophic basis for the explanation of the facts of chemical combina- 

 tion. In the early stages of its application to physics and chemis- 

 try it was unnecessary to have any detailed knowledge of the di- 



