Supplement to ''Nature,'' September 15, 1923 



419 



outlook, is able to achieve results which far transcend the 

 imagination alpne of the greatest natural philosopher. 

 Experiment without imagination^ or imagination with- 

 out recourse to experiment, can accomplish little, 

 but, for effective progress, a happy blend of these two 

 powers is necessary. The unknown appears as a dense 

 mist before the eyes of men. In penetrating this 

 obscurity we cannot invoke the aid of supermen, but 

 must depend on the combined efforts of a number of 

 adequately trained ordinary men of scientific imagina- 

 tion. Each in his own special field of inquiry is enabled 

 by the scientific method to penetrate a short distance, 

 and his work reacts upon and influences the whole body 

 of other workers. From time to time there arises an 

 illuminating conception, based on accumulated know- 

 ledge, which lights up a large region and shows the 

 connexion between these individual efforts so that a 

 general advance follows. The attack begins anew on 

 a wider front, and often with improved technical 

 weapons. The conception which led to this advance 

 often appears simple and obvious when once it has 

 been put forward. This is a common experience, and 

 the scientific man often feels a sense of disappointment 

 that he himself had not foreseen a development which 

 ultimately seems so clear and inevitable. 



The intellectual interest due to the rapid growth of 

 science to-day cannot fail to act as a stimulus to young 

 men to join in scientific investigation. In every branch 

 of science there are numerous problems of fundamental 

 interest and importance which await solution. We 

 may confidently predict an accelerated rate of progress 

 of scientific discovery, beneficial to mankind certainly 

 in a material, but possibly even more so in an intellectual 

 sense. In order to obtain the best results, certain 

 conditions must, however, be fulfilled. It is necessary 

 that our universities and other specific institutions 



should be liberally supported, so as not only to be in 

 a position to train adequately young investigators of 

 promise, but also to serve themselves as active centres 

 of research. At the same time there must be a reason- 

 able competence for those who have shown a capacity 

 for original investigation. Not least, peace throughout 

 the civilised world is as important for rapid scientific 

 development as for general commercial prosperity. 

 Indeed, science is truly international, and for progress 

 in many directions the co-operation of nations is as 

 essential as the co-operation of individuals. Science, 

 no less than industry, desires a stability not yet achieved 

 in world conditions. 



There is an error far too prevalent to-day that science 

 progresses by the demolition of former well-established 

 theories. Such is very rarely the case. For example, 

 it is often stated that Einstein's general theory of 

 relativity has overthrown the work of Newton on 

 gravitation. No statement could be further from the 

 truth. Their works, in fact, are scarcely comparable, 

 for they deal with different fields of thought. So far 

 as the work of Einstein is relevant to that of Newton, 

 it is simply a generalisation and broadening of its basis ; 

 in fact, a typical case of mathematical and physical 

 development. In general, a great principle is not 

 discarded, but so modified that it rests on a broader 

 and more stable basis. 



It is clear that the splendid period of scientific 

 activity which we have here reviewed owes much of its 

 success and intellectual appeal to the labours of those 

 great men in the past, who wisely laid the sure founda- 

 tions on which the scientific worker builds to-day, or 

 to quote from the words inscribed in the dome of the 

 National Gallery, " The works of those who have stood 

 the test of ages have a claim to that respect and 

 veneration to which no modern can pretend." 



Scientific Problems and Progress.^ 



Summaries of Addresses of Presidents of Sections of the British Association. 



The Origin of Spectra. 



THE focus of Prof. McLennan's remarks in his. pre- 

 sidential address to Section A (Mathematics and 

 physics), to be delivered on September 17, is Bohr's 

 leory of the origin of radiation and of atomic structure. 

 Evidence in support of the theory is drawn largely 

 fom recent researches on the spectra of the elements. 

 Am Mil the subjects discussed are the significance 

 tlie iirie structure of the spectral lines of hydrogen 

 id the recent attempts to devise a model of the 

 ielium atom capable of accounting for the ciiaracter- 

 istics of the helium spectrum. 



In dealing with the question of the genesis of atoms 

 '»f various tvpcs, illii>trations are given of the view 

 rcccntlv put lurward bv Bohr that the fundamental 

 process tliut iiuist apply rDnsists in the successive 

 binding of electrons 1)\- ;i nmlciis oriuinalK iiiikcd. 

 iiohr's scheme of electronic orbits lor tin jtoni.-. of 

 different elements provides ;i nicjiis ot (■■.tablishing a, 



' All 1:, .1 in full in ''The Adv..nce- 



connexion between spectral series formulae of different 

 types and the energy levels in atoms and, also, of 

 deducing the values of resonance and ionisation 

 potentials, hitherto undetermined, for a number of 

 elements. Special attention is paid to the elements 

 of the lead-tin and chromium-manganese groups. 



A number of illustrations are given of the Kossel- 

 Sommerfeld Displacement Law, and the importance 

 of the recent work of Fowler and of Paschen in this 

 connexion is emphasised. Spectroscopic data, recently 

 obtained, that are likely to lead to extensions of this 

 work are also discussed. 



In dealing with the magnetic properties of certain 

 contiguous elements, anomalies are referred to that 

 apparently do not find so ready an explanation with 

 Bohr's scheme of electronic orbits for the atoms of 

 successive elements as the Kossel-Sommerfcld Dis- 

 placement Law. Reference is also made to the prin- 

 ( iple of quantisation in space recently lironglu into 

 prominence by the interesting experiments of (Icrlacli 

 and Stern and by the work of K. VV. Wood and Ellett. 



