SECTIONAL TRANSACTIONS.— A. 353 



The electrons in number N, which surround the nucleus of an atom of 

 atomic number N, are distributed in a certain number of regions, each 

 characterised by the work wiiich it is necessary to expend in order to remove 

 an electron from the region under consideration and bring it to the exterior 

 of the atom; if the levels of these regions are designated by the letters K, L, 

 M, ... we can attribute to them energies of extraction having the values 

 Wk, Wl, Wm. . . . 



What appears to happen is that if light of frequency y strikes one of these 

 electrons, situated for example in the region K, it communicates energy equal 

 to h" in order to extract the electron from the atom ; it is clear that the cor- 

 puscle, once removed from the atomic edifice, will possess a resultant energy 

 equal to 



hi' - Wk. 



This, if we wish, we may regard as a form of the equation formerly pro- 

 posed by Einstein in the case of photo-electric phenomena ; Sir Ernest Ruther- 

 ford, some time ago, used considerations of this nature for the purpose of 

 specifying a possible connection between the natural fS and y rays of radio- 

 active substances. 



Certain expejimefital results obtained by Barkla have led him to believe that 

 ail the 13 rays excited by a beam of mono-chromatic X-rays have the same 

 energy, but other conclusions due to Lewis Simons would point, on the contrary, 

 to the role of the levels of energy. 



The method of the magnetic spectra of /3-ray velocities enables us to analyse 

 the complex bundle of corpuscles emitted by a certain radiator under X-ray 

 illumination ; experience shows that one finds there precisely all those groups of 

 electrons which can be anticipated as a consequence of the preceding considera- 

 tions ; each line of the spectrum of the incident X-rays re-echoes on each level 

 of the illuminated atom in such a way that we obtain at once an analysis both 

 of the spectral lines of the illuminating beam and of the Bohr levels of the 

 illuminated atom. 



This analysis is made without the intervention of a crystal, that is to say. 

 without encountering the limitation which results from its use in the case 

 of diffraction spectra. It furnishes by means of the measurement of the curva- 

 ture of a ray and of a magnetic field a method of checking the crystal spacings 

 which have been used in the beautiful work of Sir William Bragg and his son 

 as the basis for the evaluation of the wave-lengths of X-rays. 



INIr. Ellis has been able to show that the relation found for X-rays extends 

 also to y.rays, and makes available for the study of these rays a new device 

 already full of rich promise. 



10. Prof. E. Whiddington. — X-Ray Electrons. 



11. Sir Napier Shaw, F.E.S. — Convection in the Atmosphere. 



12. Prof. J. Proudman. — Lecture on Tides, with special reference 



to the North Sea. 



Monday, September 11. 



13. Joint Discussion with Section I on Physical Instruments 



for Biological Purposes. Opener: Prof. A. V. Hill, F.E.S. 



14. Prof. H. H. Turner, F.E.S. — Report of Seismology Committee. 



(See p. 253.) 



15. Prof. H. H. Turner, F.E.S. described the proposed new 54-ft 



Interferometer for Mount Wilson Observatory. 



16. Exhibition of Physical Apparatus for Biological Purposes. 



(a) By Major W. S. Tucker, i. Apparatus for Testing Hearing. 



This apparatus consists of two essential parts : (1) the source of sound, called 

 the transmitter, (2) the receiver. 



B B 2 



