274 



NA TURE 



[July 19, 1906 



researches on radio-activity. At this time Prof. H. B. 

 Owens, of the engineering building, had noted the 

 peculiar inconstancy of the radiations from thorium, 

 and traced it to air currents. Prof. Rutherford then 

 made an exhaustive examination of the phenomena, 

 and he found that tliorium emitted a gaseous sub- 

 stance, to which he gave the name "emanation." 

 He also proved that the emanation had the remarlc- 

 able property of making other substances active by 

 a material surface deposit due to the emanation. 

 Assisted by Miss Brooks, he proceeded to measure 

 the rate of diffusion of the emanation from radium, 

 for he then saw, and saw correctly, that the emana- 

 tion was a gas and a distinct form of matter. 



At this point Mr. Soddy came from Oxford to 

 McGill University and worked with Prof. Rutherford. 

 Together they tried the effect of varying the physical 

 conditions, such as temperature, upon the emanating 

 power of radio-active substances, and in the course of 

 this work it was found that the emanation came 

 from thorium X, a substance which could be separated 

 from thorium. When they realised and clearly proved 

 that the emanation was produced from thorium X, 

 that thorium X constantly appeared from thorium, 

 and as constantly decayed, that the curves of decay 

 and of recovery were strictly complementary, and 

 followed with e.xactitude simple exponential laws, 

 that the rate of change was proportional to the 

 amount of material still unchanged, then for the 

 first time a most clear conception of the sequence 

 of production of matter in fresh forms, with distinct 

 chemical properties, was attained. The substances 

 thus discovered were in quantities too minute to be 

 detected by the balance or spectroscope. The new 

 theory of radio-activity was published in two papers 

 by Rutherford and Soddy in the Philosophical 

 Magazine of September and November, 1902. In 

 these papers the experimental evidence was first re- 

 viewed, and then the theory was stated that radio- 

 activity is an atomic phenomenon accompanied by 

 chemical changes in which new types of matter are 

 produced, that the changes must occur within the 

 atom, and that the radio-active substances must be 

 undergoing transformation. This theory on its first 

 appearance was regarded by many as a mere flight 

 of the imagination, and efforts were made to detect 

 a cause exterior to the atom. The theory was stoutly 

 championed by Rutherford in the face of doubt and 

 criticism, and it is now so thoroughly accepted bv 

 all who have investigated the subject that the initial 

 opposition is almost forgotten. It is remarkable that 

 a new subject should have reached the position of an 

 exact science with such great rapidity. 



Experimental research continued at McGill with 

 speed which was almost feverish. Having estab- 

 lished the fact that the highest temperatures obtain- 

 able had no effect on the rate of transformation of 

 the emanation of radium, it was desired to try the 

 effect of extreme cold. Again the good genius of 

 the Physics Building was invoked, and a complete 

 plant for making liquid air was presented. Within 

 a quarter of an hour after the first 100 c.c. of liquid air 

 were prepared the emanation had been condensed, 

 and the material nature of this gas had been proved 

 beyond question. 



It is noteworthy that in the paper on the cause 

 and nature of radio-activity in the Philosophical 

 Magazine of November, 1902, the speculation was 

 advanced that the presence of helium in minerals 

 associated with uranium and thorium might be con- 

 nected with their radio-activity. In T904 this forecast 

 was verified by the observation of the presence of 

 helium in the spectrum of the radium emanation bv 



NO. 1916, VOL. 74] 



Ramsay and Soddy in the laboratory of the former. 

 In the meantime Rutherford had proved by magnetic 

 deflection that the a particles carried a positive 

 charge. The remarkable heating effects of radium, 

 three-quarters of the total amount being due to the 

 emanation, were investigated and measured. At a 

 later date the heat generated by the 7 rays was 

 under observation and found to be very small, a result 

 of importance in estimating the nature of the rays. 

 In these heat determinations Prof. Rutherford was 

 assisted by Dr. Barnes. In 1902 Mr. Soddy left 

 McGill University, worked for a year with Sir William 

 Ramsay, and was then appointed lecturer in physical 

 chemistrv at Glasgow University. Prof. Rutherford 

 continued his research work with unabated energy 

 and success. Radio-tellurium and polonium were re- 

 legated to their proper places among the products of 

 radium, now grown to a family of six, the successive 

 offspring of the emanation. The theory of rayless 

 changes was advanced, and the coinplicated cases 

 arising therefrom were thoroughly explored, and the 

 results published in the Bakerian lecture delivered 

 before the Royal Society in 1904. The brilliant work 

 of Rutherford received recognition bv the award to 

 him of the Rumford medal. More recently he has 

 again directed his attention to the a particles, 

 deflecting in electric and magnetic fields the rays 

 from radium C and other substances, thus determin- 

 ing the charge and mass of the particles, and en- 

 deavouring to account for their abrupt disappearance 

 whilst their velocities are still very great. 



So much work and such novel theories have natur- 

 ally called forth criticism, but the discussions have 

 always been chivalrous, buttons have been on the 

 foils, and Rutherford's extreme care in verifying every 

 step by thorough experimental evidence has saved 

 him from error to a degree quite exceptional. A 

 prominent physicist in the early days of radio-activity 

 remarked that the subject was such a tangled skein 

 that it was almost hopeless to unravel it. This sufifi- 

 cientlv indicates the difficulty of the subject in the 

 initial stages. It is fortunate that so much of the 

 development centred in a man to whom the remark- 

 able instinct is given of rarely following side-issues. 

 .\s a result of this concentration a uniform system 

 of nomenclature has been adopted, and experimenters 

 are saved much time and trouble in following the 

 work of others, .\part from such concentration, it 

 is not difficult to imagine the state of chaos into 

 which the whole subject would have lapsed. Ruther- 

 ford's work, " Radio-activity," has passed rapidly 

 through two editions, has kept pace with discoveries, 

 and is the encycloDsedia of the subject. 



At the phvsics building Prof. Rutherford inspires 

 research students with some of his own enthusiasm 

 and enerary. He follows their results closelv. is readv 

 with advice and criticism, and is as deliarhted with any 

 of their discoveries as with hi.s own. He is generositv 

 itself in giving a full measure of credit to those who 

 do research work under his guidance. 



Reference may be made to some of the work done 

 by research students. Miss Brooks has published 

 several papers on various radio-active phenomena, and 

 this lady was one of the most successful and indus- 

 trious workers in the earlv days of the investigation 

 of the subject. H. L. Cooke discovered penetrating 

 rays from the earth, and made contributions on the 

 activitv of ordinarv matter. R. K. McClung deter- 

 mined the coefficient of re-combination of ions, and 

 worked with Rutherford on the energv required to 

 produce an ion, and on allied problems. S. J. .Mian 

 worked at the active deposit derived from the atmo- 

 sphere and from falling snow. Miss Gates ascer- 



