Intelligence and Miscellaneous Articles. 755 



conclusions drawn from the analysis, will be published in due 

 course. 



The Committee would be greatly aided in the organization of 

 this investigation if those possessing the necessary facilities and 

 willing to make observations during the eclipse would communicate 

 with the Hon. Secretary, Dr. W. Eccles, University College, 

 London, W.C., at the earliest possible date. 



ON THE RECOMBINATION OF IONS MADE BY a RAYS. 



To the Editors of the Philosophical Magazine. 



Gentlemen, 



In a paper in the December number of the Philosophical 

 Magazine Mr. Ogden describes some experiments on initial recom- 

 bination of ions. As the exact nature of the effect appears to 

 have not yet been made quite clear by the various experiments on 

 the subject (Moulin's explanation is not sufficient), I would like 

 to point out one of the causes operating (of which there are 

 probably several) which would make a dense pencil of ions in a 

 gas behave different from a uniform distribution. This may be 

 helpful in carrying out further investigations on the subject. If 

 each of the electrons ejected by the a, particle on the average does 

 not form a cluster as the result of a single collision with a neutral 

 molecule, there would exist initially principally general recombi- 

 nation between free negative ions or electrons and positive ions. 

 The disappearance of ions would thus to a certain extent depend 

 on the average period of life of an electron before forming a cluster, 

 and on the coefficient of recombination of free electrons and posi- 

 tive ions. I have obtained experimental evidence that an electron 

 undergoes a large number of collisions before it successfully forms 

 a cluster, which will be dealt with fully in a paper which will 

 appear shortly. The period of life of an electron and the co- 

 efficient of recombination of electrons and positive ions probably 

 depend considerably on the nature of the gas. We do not know 

 anything yet about the latter quantity, but it is probably greater 

 than the coefficient of recombination measured in the usual way, 

 in which case recombination occurs between negative clusters and 

 electrons and the positive ions. This would explain the intense 

 effects obtained. 



Yours faithfully, 



E. D. Kleemax. 



lo tlie Editors of the Philosophical Magazine, 



Gentlemen, 



In a paper published in the Proceedings of the Royal Society, 

 A. vol. S3, p. 376 (1909), I showed that the collision current 

 between an aluminium plate and leaf in a gas at a pressure o\' 



