August 5, 1922] 



NA TURE 



1S5 



oxygen scale, the helium atom has a mass very nearly 

 4-000, while the hydrogen atom has a mass 1-0077. 

 The mass of the helium atom is thus considerably less 

 than that of four free H nuclei. Disregarding the small 

 mass of the electrons, in the formation of 1 gram of 

 helium from hydrogen there would be a loss of mass 

 of 7-7 milligrams. 



It is now generally accepted that if the formation 

 of a complex system is accompanied by the radiation 

 of energy E, the reduction of the mass m of the system 

 is given by E=mc 2 , where c is the velocity of light. 

 This relation between mass and energy follows not 

 only as a direct consequence of the theory of relativity, 

 but can be derived directly from Maxwell's theory, as 

 pointed out by Larmor. On this relation, the energy 

 E liberated in the formation of 1 grm. of helium from 

 hydrogen is equal to 6-9 x io 18 ergs or i-6 x io 11 gramme- 

 calories. This is an enormous amount of energy, large 

 compared even w-ith the total energy emitted during 

 the complete disintegration of 1 grm. of radium and 

 its products, namely, about 3-7 x io 9 gramme-calories. 

 It can be calculated that the energy radiated in forming 

 one atom of helium is equivalent to the energy carried 

 by three or four swift a-particles from radium. On this 

 view we can at once understand why it should be im- 

 possible to break up the helium nucleus by a collision 

 with an a-particle. In fact, the helium atom should 

 be by far the most stable of all the complex atoms. 



It has been pointed out by Perrin and Eddington 

 that in all probability the energy of radiation from our 

 sun and the stars is derived mainly from the enormous 

 emission of energy accompanying the formation of 

 helium from hydrogen. If this be the case, it is easy 

 to show that sufficient energy can be derived from this 

 source for our sun to radiate at its present rate for 

 several thousand million years, whereas the older 

 theories of Kelvin and Helmholtz, in which the heat 

 of the sun is ascribed to the gradual concentration of 

 the material under gravity, make the life of the sun 

 much shorter than modern estimates of the age of the 

 earth and appear to be quite inadequate to provide 

 the requisite energy. 



This interesting suggestion of the probable origin of 

 the greater part of the enormous energy radiated by 

 the sun and stars is one of the first-fruits of the in- 

 vestigations on the structure of atoms. It is believed 

 that the formation of helium from hydrogen occurs 

 under certain conditions in the great central furnace 

 of the sun and stars, but there is no evidence, so far, 

 that this combination can be produced under laboratory 



conditions. It may be that it can be effected only 

 under conditions of very high temperature and 

 enormous intensity of radiation such as occur in the 

 interior of a sun. Even then the process of formation 

 may go on at a very slow rate and for periods measured 

 by millions of years. 



Most workers on the problem of atomic constitution 

 take as a working hypothesis that the atoms of matter 

 are purely electrical structures, and that ultimately 

 it is hoped to explain all the properties of atoms as a 

 result of certain combinations of the two fundamental 

 units of positive and negative electricity, the proton 

 and electron. Some of the more successful methods 

 of attack that have been made on this most difficult 

 of problems have been indicated. During recent years, 

 unexpectedly rapid advances have been made in our 

 knowledge, but we have only made a beginning in the 

 attack on a very great and intricate problem. 



Great difficulties arise the moment we consider why 

 the nucleus of an atom holds together, and progress 

 seems likely to be slow because it seems clear that 

 the ordinary laws of force between electrified particles 

 break down at such minute distances. There are, how- 

 ever, a number of obvious lines of attack that may yield 

 us very valuable information. In particular, a closer 

 study of the modes of transformation of radio-active 

 bodies, where the process of devolution of elements 

 takes place before our eyes, may be expected to give 

 much important data. During recent years the study 

 of the y- or very penetrating X-rays from radio-active 

 bodies has progressed very rapidly. The general 

 evidence indicates that the y-rays, like the a- and ji- 

 particle, have their origin in the nucleus. The study 

 of the y-rays thus gives us information of the frequency 

 of vibration of the electrons which form part of the 

 nuclear structure. In addition, Ellis has shown that 

 it appears probable that the laws of quantum dynamics 

 which govern the motions and vibrations of the outer 

 electrons apply also to the nuclear electrons. If this 

 conclusion can be verified, it offers the hope that we 

 may be able later to form some idea of the detailed 

 structure of nuclei. There are also a number of other 

 lines of evidence that will have to be taken into account 

 in formulating any definite theory of the evolution 

 of the elements ; for example, Harkins has pointed 

 out some very interesting relations that appear to exist 

 between the relative abundance of elements in the 

 earth and their atomic number, while the close study 

 of stellar evolution should ultimately throw much light 

 on the general problem. 



The Royal Botanic Society's Gardens. 



THE gardens of the Royal Botanic Society, 

 Regent's Park, are one of the landmarks of 

 London. They occupy the whole of the Inner Circle 

 of Regent's Park, an area of nearly 20 acres. The 

 accompanying aerophotograph shows very well their 

 main features. The Society was established by Royal 

 Charter in 1839, " for the promotion of botany in all 

 its branches, and its application to medicine, arts, and 

 manufactures, and also for the formation of extensive 

 botanical and ornamental gardens within the immediate 

 vicinity of the metropolis." The first president was 

 the Duke of Richmond, and the first secretary James 



NO. 2753, VOL. I io] 



De Carle Sowerby. a botanist and artist, whose father, 

 James Sowerby, was a well-known botanist in his time. 

 The latter was author of " English Botany," a classic 

 collection of coloured drawings of British plants, and 

 ] other works. The son, James De Carle Sowerby. in- 

 herited his father's tastes as a botanist and artist. He 

 also handed on to his son and grandson the office of 

 secretary, the latter resigning shortly before the war. 



Their Majesties the King and Queen and Queen 

 Alexandra, and H.R.H. the Prince of Wales are patrons 

 of the society, and the present President is Viscount 

 Lascelles. The grounds of the gardens were originally 



