REVIEWS 699 



these days of two and three circle goniometers such tables would be prepared with 

 the minimum of trouble and calculation. 



One of the most valuable features of the book is the description of the delicate 

 apparatus devised by the author for carrying out the exact measurements which his 

 researches necessitated. The cutting and grinding goniometer by which thin 

 sections in any required direction may be obtained with the greatest accuracy ; 

 the monochromatic illuminator by which light of any required wave-length is 

 available for optical work ; the interferometer which enables the most trifling 

 movement of a plane surface in the direction of its normal to be observed ; and 

 the dilatometer and elasmometer by which such observations are applied to the 

 determination of the linear expansion with increase of temperature and of the 

 elasticity of crystal plates. 



Dr. Tutton has resisted the temptation to indulge in the speculations on crystal 

 structure to which the subject and his results would so easily lend themselves, 

 preferring to dwell on the important and suggestive facts which his careful work 

 has revealed. He has not always, however, we learn from the introductory pages, 

 restrained his scientific imagination so severely. He gives us an interesting 

 quotation from an essay published as early as 1884 in the Science Schools Journal, 

 entitled " Protylian Vapourings " : 



" Let us say that an atom of hydrogen contains x primary particles or atoms, 

 held together by their inertia of revolution, then our theory says that sodium 

 contains 23.1' primary atoms ; consequently the ring must be more closely packed, 

 and less energy can be externally manifested. Similarly potassium has 39^ 

 primary particles to the atom, and mercury 200 .r primary particles." 



If, as Dr. Tutton suggests, we read "electronic corpuscles" for "primary 

 particles," the passage represents very fairly the views now held on the con- 

 stitution of matter. 



John W. Evans. 



The Interpretation of Radium. By Frederick Soddy, M.A. [Pp. viii + 256.] 



(London : John Murray, 1909. Price 6s. net.) 



This book contains an accurate presentation in non-technical language of the 

 modern interpretation of radium, namely, that it is an element undergoing spon- 

 taneous disintegration. The text is based upon the subject-matter of a course 

 of lectures delivered recently by the author in the University of Glasgow. It is 

 pointed out at the beginning that the science of Radioactivity is not an expansion 

 or extension of existing principles but a new step regarding the ultimate nature of 

 the atom. The fact that the author, in conjunction with Prof. Rutherford, carried 

 out much of the work which laid the foundations of the hypothesis of atomic 

 disintegration, increases considerably the interest of the book. 



The opening chapters deal with the experimental effects of radioactivity, the 

 continuous emission of energy by radio-elements, and the properties of the o-, £-, 

 and y-rays. The two alternatives, as to whether the energy of radioactive 

 elements comes from outside sources or from within the atom itself are discussed, 

 and it is shown that the weight of evidence is in favour of the latter assumption. 

 The book then deals with the properties of the various bodies which are formed by 

 radioactive changes. Starting with Uranium (atomic weight, 238) the changes are 

 traced down to Radium G (atomic weight, 206. Lead ?). Many admirable experi- 

 ments are described in the text : the spinthariscope for counting a-particles, the 

 radium clock, the geological interest attaching to radioactivity and many other 

 interesting subjects are dealt with. 



