Chemistry and Physics. 461 



Professor E, Rutherford, in the Philosophical Magazine for 

 August, 1906, has an article on the "Retardation of the a-particle 

 from Radium in passing through Matter." " The photographic 

 effect of the a-particles toward the end of their path in air 

 decreases far more rapidly than the kinetic energy of the a-parti- 

 cles themselves. It is possible to determine with accuracy the 



7)% V 



value for the a-particles emitted by radium, radium A, and 



radium F by measurements of the retardation of the a-particles of 

 the single product radium C in passing through matter. Such a 

 result affords an almost certain proof that the value of e/mis 

 the same for the a-particles expelled from each of these products." 

 The same author discusses the intensity of radiation from radio- 

 active sources, and contrasts the photographic effect of radium 

 emanations through apertures of various forms with the radiation 

 of the sun. In the case of the latter, Lambert's law.of cosines 

 applies ; that is,- the intensity of radiation from any point varies 

 as the cosine of the an^le between the normal and the direction 

 of the emitted light. This law does not apply to a thin layer of 

 radio-active substance. Hence we find great inequalities in the 

 distribution of the photographic effects. A number of photo- 

 graphs accompany the paper (Phil. Mag., August, 1906). 



The September number of the same journal contains an article 

 by M. Levin, " On the Origin of the /3-rays emitted by Thorium 

 and Actinium." M. Levin has been working with Professor 

 Rutherford. It was found that actinium by itself is a rayless 

 substance. A remarkable similarity was found to exist between 

 the modes of transformation of thorium and actinium. The 

 same journal contains a paper " On the Radioactive Matter in 

 the Earth and the Atmosphere," by A. S. Eve, communicated by 

 Professor Rutherford. The author believes that emanation exists 

 in the atmosphere, but thinks that more experimental work must 

 be done before any exact value can be assigned to the number of 

 ions produced. 



" About 1*8 X10 -11 grams of radium bromide is the estimated 

 equivalent of the active matter per c.c. present in the earth's 

 crust sufficient to account for the penetrating radiation. This 

 appears to be about four times as large as the average amount 

 found by Strutt by direct observation of rock specimens. The 

 ionization of the atmosphere is due partly to penetrating radia- 

 tion from the active matter in the earth, partly to a-radiation 

 from the emanation in the atmosphere." J. t. 



8. Velocity of X-Rays. — E. Marx describes minutely his 

 investigation of this velocity. The method depends" primarily 

 upon the property which the X-rays possess of ionization of a 

 gas. Electric waves were produced along parallel wires accord- 

 ing to Lecher's system. The velocity of these waves was assumed 

 to be the same as the velocity of light. A Rontgen tube was, 

 therefore, so connected with the Lecher system, that the differ- 

 ences of potential due to the presence of nodes or ventral seg- 



