August 22, 1913] 



SCIENCE 



275 



E = charge of an a ray ; 

 m = mass of an o ray; 

 u = velocity of an a ray. 



More recently, Geiger and Marsden° have per- 

 formed a very thorough series of experiments 

 which verify this formula, within an experi- 

 mental error of about 20 per cent., for wide 

 variations of ni, u and <^. In addition, by 

 testing foils of various metals they found that 

 P is proportional to the square of the atomic 

 weight of the bombarded metal, other things 

 being the same. Their experiments prove, 

 then, that, for gold, platinum, tin, silver, 

 copper and aluminium, 



P = K- 



m 



where A is the atomic weight. The striking 

 agreement of their results with the predictions 

 of the Rutherford theory certainly lend it 

 great support. It surely deserves careful con- 

 sideration to see whether other conclusions 

 from it may be tested experimentally and 

 whether other atomic phenomena may be ex- 

 plained by it. Assuming the correctness of the 

 Rutherford formula, Geiger and Marsden com- 

 puted from an absolute determination of Q 

 and the other quantities involved, the positive 

 charge which must be assumed to be concen- 

 trated at the centers of the atoms of the metals 

 investigated ; and they found that it is, within 

 20 per cent., numerically equal to half the 

 atomic weight in each case times the charge of 

 an electon; that is. 



^ = 4 (1 ^ 



:.2); 



a most important conclusion, if true. 



Evidently, since hydrogen can not have as 

 a nucleus a charge of -j- Je, it must be an ex- 

 ception ; the above law can not hold for all the 

 elements. In this connection some experiments 

 of Kleeman* on the relative ionization in vari- 

 ous gases, are of interest. He found that the 

 ionization per cubic contimeter of various com- 

 pound gases by a given agent can be predicted 

 from the ionization by the same agent of the 



= PML Mag., 25: 604, April, 1913. 

 *Proc. Soy. Soc, 79A: 220, 1907; 

 1910. 



separate elements composing the compounds; 

 that is, ionization is roughly an additive, 

 atomic property. From the results obtained 

 with a number of simple and compound gases, 

 he computed approximately the atomic ioniza- 

 tion for various elements as given in the fol- 

 lowing table:" 



83A: 530, 



While other factors enter, such as the valence 

 or the position of the elements in the periodic 

 table and chemical linkage with other atoms, 

 atomic ionization seems to depend primarily 

 on the atomic weight, which is probably pro- 

 portional to the number of electrons in the 

 atom. The fact that hydrogen has approxi- 

 mately twice the atomic ionization which 

 should correspond to its atomic weight, sug- 

 gests that it may have twice as many electrons 

 in proportion to its atomic weight as the other 

 elements — in agreement with the above con- 

 clusion from the Rutherford theory. It is 

 also noteworthy that canal ray deflection ex- 

 periments performed by Sir J. J. Thomson, 

 Wien, Koenigsberger and others have given 

 no evidence for the existence of doubly 

 charged hydrogen atoms in a discharge tube, 

 whereas doubly charged atoms of other gases 

 are often present. This would tend to con- 

 firm the conception of the hydrogen atom 

 as a small positive nucleus with a single elec- 

 tron revolving as a satellite around it. 



As for helium, we may suppose, perhaps, 

 that a particles, since they are projected from 

 radioactive substances with such enormous 

 velocities, are stripped of all satellite elec- 

 trons; that a particles are merely positive 

 nuclei with a charge of + 2e. If so, the num- 

 ber of satellite electrons in the neutral helium 



'Proc. Boy. Soc, 79A: 220, 1907. 



