488 Sir E. Rutherford on the 



include the possibility that the part of f thus arising, is not 

 negligible we might have defined <p(v) rather differently as 

 the excess at emission of the internal kinetic energy over the 

 mean value f . In that case some of the other conclusions 

 would require reconsideration. Also, the results which have 

 been given are not easily harmonized with the values of the 

 specific heats of bodies at low temperatures. For these 

 reasons, the formulation outlined above is to be taken as illus- 

 trative rather than final. Another direction in which it 

 is practically certain that the foregoing theory is too 

 much simplified is in the assumption of only one critical 

 frequency v . I hope to be able to return to the discussion 

 of these questions later. 



Palmer Physical Laboratory, 

 Princeion, N. J. 



L VII. The Structure of the Atom. By Sir Ernest Rutherford, 

 F.R.S., Professor of Physics, University of Manchester*. 



ri^HE present paper and the accompanying paper by 

 JL Mr. C Darwin deal with certain points in connexion 

 with the " nucleus " theory of the atom which were pur- 

 posely omitted in my first communication on that subject 

 (Phil. Mag. May 19ll). A brief account is given of the 

 later investigations which have been made to test the theory 

 and of the deductions which can be drawn from them. At 

 the same time a brief statement is given of recent observa- 

 tions on the passage of a particles through hydrogen, which 

 throw important light on the dimensions of the nucleus. 



In my previous paper (loc. cit.) I pointed out the import- 

 ance of the study of the passage of the high speed « and [3 

 particles through matter as a means of throwing light on 

 the internal structure of the atom. Attention was drawn 

 to the remarkable fact, first observed by Geiger and 

 Marsden f, that a small fraction of the swift « particles 

 from radioactive substances were able to be deflected 

 through an angle of more than 90° as the results of an 

 encounter with a single atom. It was shown that the type 

 of atom devised by Lord Kelvin and worked out in great 

 detail by Sir J. J. Thomson was unable to produce such 

 large deflexions unless the diameter of the positive sphere 

 w«s exceedingly small. In order to account ior this large 

 angle scattering of a particles, I supposed that the atom 

 •consisted of a positively charged nucleus of small dimensions 



* Communicated by the Author. 



t Proc. Poy. Soc. A. lxxxii. p. 495 (1909). 



