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Supplement to ''Nature" Septcno^y 15, 1923 



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 i)oint at the moment, for the importance 

 of a training in pure research has been generally recog- 

 nised. 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 for both 

 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 ad- 

 minister 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 here to refer very briefly to some 

 of the main features of that great advance in know- 

 ledge 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 

 to have any detailed knowledge of the dimensions 

 or structure of the atom. It was only necessary to 

 assume that the atoms acted as individual units, and 

 to know the relative masses of the atoms of the different 

 elements. In the next stage, for example, in the 

 kinetic theory of gases, it was possible to explain the 

 main properties of gases by supposing that the atoms 

 of the gas acted as minute perfectly elastic spheres. 

 During this period, by the application of a variety of 

 methods, many of which were due to Lord Kelvin, 

 rough estimates had been obtained of the absolute 

 dimensions and mass of the atoms. These brought out 

 the minute size and mass of the atom and the enormous 

 number of atoms necessary to produce a detectable 

 effect in any kind of measurement. From this arose 

 the general idea that the atomic theory must of 

 necessity for ever remain unverifiable by direct ex- 

 periment, and for this reason it was suggested by one 

 school of thought that the atomic theory should be 

 banished from the teaching of chemistry, and that the 

 law of multiple proportions should be accepted as the 

 ultimate fact o£ chemistry. 



Wliile the vaguest ideas were held as to the possiM- 

 structure of atoms, there was a general belief ani _ 

 the more philosophically minded that the atoms ol 

 the elements could not t)e regarded as simple un- 

 connected units. The periodic variations of ?'<• 

 proi)erties of the elements brought out by Mendrl- 1 

 were only explicable if atoms were similar struct i.r- ^ 

 in some way constructed of similar material, \\ir 

 shall see that the problem of the constitution of atoms 

 is intimately connected with our conception of the 

 nature of electricity. The wonderful success of the 

 electromagnetic theory had concentrated attention on 

 the medium or ether surrounding the conductor of 

 electricity, and little attention had l)een paid to the 

 actual carriers of the electric current itself. At the 

 same time the idea was generally g:i' ' 

 an explanation of the results of Far.i . 

 on electrolysis was only possible on the assunipii.n 

 that electricity, like matter, was atomic in nature. 

 The name " electron " had even been given to this 

 fundamental unit by Johnstone Stoney, and its 

 magnitude roughly estimated, but the full recognition 

 of the significance and importance of this conception 

 belongs to the new epoch. 



For the clarifying of these somewhat vague ideas, 

 the proof in 1897 of the independent existence of the 

 electron as a mobile electrified unit, of mass minute 

 compared with that of the lightest atom, was of 

 extraordinary importance. It was soon seen that the 

 electron must be of a constituent of all the atoms of 

 matter, and that optical spectra had their origin in 

 their vibrations. The discovery of the electron and 

 the proof of its liberation by a variety of methods 

 from all the atoms of matter was of the utmost 

 significance, for it strengthened the view that the 

 electron was probably the common unit in the structure 

 of atoms which the periodic variation of the chemical 

 properties had indicated. It gave for the first time 

 some hope of the success of an attack on that most 

 fundamental of all problems — the detailed structure of 

 the atom. In the early development of this subject 

 science owes much to the work of Sir J. J. Thomson, 

 both for the boldness of his ideas and for his ingenuity 

 in developing methods for estimating the number of 

 electrons in the atom, and in probing its structure. 

 He early took the view that the atom must be an 

 electrical structure, held together by electrical forces, 

 and showed in a general way lines of possible ex- 

 planation of the variation of physical and chemical 

 properties of the elements, exemplified in the jjeriodic 

 law. 



In the meantime our whole conception of the atom 

 and of the magnitude of the forces which held it 

 together were revolutionised by the study of radio- 

 activity. The discovery of radium was a great step 

 in advance, for it provided the experimenter with 

 powerful sources of radiation specially suitable for 

 examining the nature of the characteristic radiations 

 which are emitted by the radioactive bodies in general. 

 It was soon shown that the atoms of radioactive matter 

 were undergoing spontaneous transformation, and that 

 the characteristic radiations emitted, namely, the a-, /?-, 

 and y-rays, were an accompaniment and consequence 

 of these atomic explosions. The wonderful succession 

 of changes that occur in uranium and thorium, more 



