February, 1913. 



KNOWLEDGE. 



77 



the Rationalists and the Intellectualists, that we must have 

 arrived at our conceptions of the Universe by utilization 

 and development of notions derived from our primary and 

 direct sense-perceptions of Motion, of Speed, and of Force. 

 Other essays deal with the philosophy of M. Bergson ; with 

 the definition of wealth ; with social reforms, and with one of 

 Sir Oliver's most practical contributions to the community's 

 immediate well-being — SmoUe Prevention. 



E. S. G. 



PHYSICS. 



The Principle! : or the First Principles of Natural 

 Things. To which are added the Minor Principia and 

 Summary of the Principia. — By Emanuel Swedenborg. 

 Translated from the Latin by James R. Rendell, B.A., and 

 Isaiah Tansley, B.A. With an Introduction by Isaiah 

 Tansley, B.A., and a Foreword by Sir William Barrett, 

 F.R.S. 2 vols. 1340 pages. 104 figures. 8^-in. X 5i-in. 



(The Swedenborg Society. Price 21/- net.) 



Swedenborg- is best known, perhaps, by his later philo- 

 sophical and theological worUs. But during the last few 

 years an increasing interest has been taken in his earlier 

 works on natural science, it having become apparent that he 

 anticipated some of the important discoveries and theories of 

 modern times in physics and cosmology. This excellent and 

 carefully prepared translation of Swedenborg's Principia will, 

 therefore, be welcomed by all physicists and cosmologists who 

 are interested in the history of science. Swedenborg con- 

 ceived of nature as the expression of the Divine Will, but 

 according to him, this Will always operates according to fixed 

 laws of order and sequence. Consequently, although 

 Swedenborg, as a philosopher, took a transcendental view of 

 nature, regarding it as a miracle ; as a worker in science he 

 treated nature as a machine, and attempted to work out a 

 complete theory of natural phenomena based on mechanics 

 and geometry. His position in this respect, is somewhat 

 similar to the attitude of that particularly clear thinker of the 

 present time, Dr. C. Lloyd Morgan. 



Whenever experimental facts were obtainable, Swedenborg 

 utilised them. But experimental science was in its merest 

 infancy in Swedenborg's day. and consequently he was 

 frequently obliged to argue a priori. This led him, in his 

 Principia, to make assumptions, which, nowadays, would not 

 be allowed. Nevertheless, his genius was far in advance of 

 his time, and enabled him more than once to get at the true 

 explanation of phenomena. He was the first to put forward 

 the concept of a vortex-atom. He regarded light as produced 

 by undulations in the ether (a theory already put forward by 

 Huygens, but discredited by Newton). He also regarded heat 

 and electricity as having an etheric origin. His explanation 

 of the reason of the magnetisation of iron, by stroking with a 

 magnet, is perfectly correct ; and his words on this point 

 might, as Sir William Barrett points out in his valuable and 

 appreciative Foreword, be those of a modern student. More- 

 over, his explanation of the orgin of the solar system must be 

 regarded as an anticipation of the theory of Laplace. Indeed, 

 Swedenborg seems to have been a man of extraordinary 

 mental abilities, whose works have been too much neglected. 

 An Appendix containing critical and explanatory notes by 

 Professor Very adds to the value of the present translation. 



H. S. Redgrove. 



RADIOACTIVITY. 



Radioactive Substances and their Radiations. — By E. 

 Rutherford, D.Sc, F.R.S. 699 pages. 8}-in.X6-in. 



(The Cambridge University Press. Price 15/- net.) 



It is eight years ago since Professor Rutherford published 

 what was rightly regarded as the authoritative work on the 

 emanations of radioactive substances, and from that volume 



many which have been written since are largely derivative. 

 In 1904 the theory of the disintegration of the atom, of which 

 Rutherford made use to explain the phenomena of the 

 expulsion of atoms and electrons, and of rays as yet not 

 entirely accounted for, was still under discussion. Lord 

 Kelvin was not entirely convinced ; and there was an alterna- 

 tive theory, not without advocates, which was that the energy 

 of radium was first taken in from an external source, and was 

 than transformed into radioactive energy by a kind of surface 

 osmosis. Professor Rutherford's answer to this suggestion 

 was to dissolve a speck of radium bromide in a solution of 

 radium chloride which was a thousand times the speck of 

 radium's bulk, and then to show that there was no alteration 

 in the rate or quality of the radiation such as there should 

 have been if the radiation had been dependent on external 

 sources of energy. 



One recalls the experiment as something almost archaic, 

 so soundly now does the disintegration theory seem estab- 

 lished. But it is of importance to notice the rate at which 

 confirmation of the theory grew. Confirmation was given to 

 it by the increasing knowledge of the transformations which 

 radium and other radioactive substances underwent, because 

 it was evident that the mechanism of transformation was the 

 same or similar in succeeding cases, and with the accumu- 

 lation of instances it became clear that the idea of unstable 

 atoms disintegrating under the influence of a disturbance to 

 the units of their atomic systems, was the only one which 

 would cover all the cases. In 1905 twenty of these trans- 

 formations in radioactive substances were known. The 

 number now is thirty-two, and Professor Rutherford remarks 

 that there is some evidence to show that a few transforma- 

 tions still remain undetected. They are not easy to find, 

 because the transformations are so extremely rapid : and in 

 consequence the lives of the elements produced by them are 

 extremely short. Radium has a life of respectable pro- 

 portion, though it is so far below the career enjoyed by its 

 venerable ancestor Uranium : but the one thousand seven 

 hundred and sixty years which are the '" half-life of radium," 

 are a comparative immortality by the side of the lifetime of 

 that element derived from the emanation of thorium, whose 

 life is only fourteen-hundredths of a second, or of the actinium 

 derivative, the lifetime of which is one five-hundredth of a 

 second. 



These are some of the results of the eight years of investi- 

 gation conducted in every physical laboratory of the world, 

 and summarised in what is, in all respects but that of theory, 

 a new volume. The eight years, however, besides affording 

 a vast amount of information, have been fecund in new 

 methods and in new ideas. The most singularly useful of 

 the new methods is, perhaps, that due to the discovery of ways 

 of counting single a particles. This has not merely extended 

 the knowledge of the a particle, but it has been of the 

 greatest importance in obtaining accurate data for the calcula- 

 tion of a number of important radioactive quantities and 

 atomic magnitudes. It must not be forgotten that it is since 

 1904 that physicists have learnt to weigh the negative 

 corpuscle. 



Again, the discovery of the recoil of radioactive particles 

 when an a particle has been expelled, has proved to be useful 

 as a means of separating radioactive substances : it has also 

 furnished a new kind of corpuscular radiation for study. The 

 importance of secondary radiations ; the light they throw on a 

 possible positive particle of electricity ; the nature of gamma 

 rays and their probable identity with Rbntgen rays — these 

 are the things which are now of most importance in the study 

 of radioactivity. To them all, as well as to the influence 

 which emanations of radioactive substances exert on the 

 electrical state of the atmosphere, Professor Rutherford gives 

 exactly the right kind of judgment and consideration. His 

 new work is one of those which are inevitably and indubitably 

 standard works : and the only corollary we could have wished 

 to add to it would be a more extended consideration of 

 Professor Bragg's theory on the nature of " electric doublets " 

 and the Rbntgen rays. H s< Kedgrove. 



