4A6 Mr. J. Crosby Chapman on Homogeneous 



the tenth is only 29'812, the number of important vibrations 

 is enormous, and an analytical solution by the method o£ 

 Walker does not appear to be possible, and what the exact 

 result would be cannot apparently be predicted. But one 

 assertion may be made with certainty. The amplitudes of 

 the free vibrations of % and f are of the same order as those 

 of the forced vibrations, in any time for which the periodic 

 force would not be disturbed by other agencies, and it is quite 

 likely that the dissipation function defining the radiation 

 may not be capable of a negative value, with absorption as a 

 consequence instead of emission. 



These remarks apply of course only to the dielectric 

 electron with such a coefficient that its free fundamental 

 vibration shall be in the visible spectrum. For a conducting 

 electron, the expression for the radiation under a periodic 

 force, with its consequence of absorption for a certain range, 

 is not affected. But arguments against the possibility of the 

 non-deformable conducting electron can be found on other 

 grounds. 



It, seems probable that when k is nearly infinite, the sum 

 of the amplitudes of the forced vibrations (excepting that 

 corresponding to the conductor) would tend to zero, leading 

 to the results for a conductor. But when the vibration is 

 constrained to be in the visible spectrum, no such conclusion 

 can be drawn. 



LII. Homogeneous Rbntgen Radiation from Vapours. By 

 J. Crosby Chapman, B.Sc, Layton Research Scholar 

 of the University of London (King's College) ; Research 

 Student of Gonville and Caius College } Cambridge *. 



ALL bodies when exposed to Bontgen radiation emit 

 secondary X-rays. It has been shown f that these 

 secondary rays consist of two types — a scattered radiation 

 having the same penetrating power as the primary beam and 

 resembling it in that it is heterogeneous and an X radiation 

 characteristic only of the element used as radiator and 

 independent of the penetrating power of the exciting primary 

 beam. 



The elements belonging to the group w T ith atomic weights 

 from hydrogen to sulphur have been shown to give out, when 

 excited, a great preponderance of the first type of radiation 

 termed scattered radiation {, while those in the group from 



* Communicated by Prof. C. G. Barkla, M.A., D.Sc. 

 t Karlda & Sadler/ Phil. Mag. Oct. 1908. 

 \ Barkk, Phil. Mag-. June 1903. 



