RECENT ADVANCES IN SCIENCE 209 



3 x icr 13 cm. Physicists have on occasion assumed the inverse 

 square law to hold down to distances of the order 3 x io -12 cm., 

 without reaching conclusions discrepant with observation ; but 

 this distance of approach is ten times as small, and at such a 

 distance — comparable with the dimensions of the electron 

 itself — assumptions as to point charges and inverse square law 

 must become very doubtful. Rutherford points out that at 

 such a close distance an a particle composed of four hydrogen 

 nuclei and two electrons would exert a very complicated field of 

 force with rapid variations in direction and magnitude ; further, 

 that the very considerable forces involved between two positive 

 nuclei at such a distance — about 5 kilograms weight on the 

 inverse square law — must distort not only the structure of the 

 nucleus itself, but even of the electron. It is probably this 

 distortion, and the consequent alteration in the magnitude and 

 direction of the forces involved, which are responsible for the fact 

 that a greater proportion of the collisions are of the " head-on " 

 or nearly " head-on " type than could be anticipated on the 

 simple theory of point-charges. 



The second of the papers deals with an investigation by the 

 usual magnetic and electrostatic deflexion methods of the 

 velocity and e/m ratio of the swift particles in these experiments, 

 yielding support to the assumption that they are H nuclei. 

 The third deals with experiments on collision between a particles 

 and atoms of nitrogen and oxygen. Theoretically it is to be ex- 

 pected that all atoms of weight not greater than that of oxygen, 

 and carrying unit electronic charge, might be detected in such 

 experiments beyond the range of the impinging a particles ; 

 thus N atoms could have a maximum range 1*33 times as great, 

 and O atoms 1-12 times as great, as the range of the a particles. 

 Preliminary experiments have been made with other atoms, 

 but they are difficult to cany out, and the results rather incon- 

 clusive ; but for elements in the gaseous state, such as N and O, 

 conditions are much better. Briefly, Rutherford finds evidence 

 for the existence of swift N and O particles in air, nitrogen, 

 oxygen, and carbon dioxide, with maximum range about 9 cms. 

 in air. As in the case of H atoms, the observed numbers for any 

 given fraction of the range and over are larger than the numbers 

 calculated on simple theory, and a similar explanation must 

 hold here. It is in the fourth paper that Prof. Rutherford 

 really deals with a matter of supreme importance — viz., the 



