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XXI. Evidence that Rontgen Rays are Ordinary Light, 

 To the Editors of the Philosophical Magazine, 

 Gentlemen, 



YOU will oblige me very much if you afford me space to 

 supply an omission from the paper in the June number 

 of the Philosophical Magazine which adduces evidence that 

 Eontgen rays are ordinary light of shortwave-length ; and if 

 you also allow me to present a summary of the results arrived 

 at in that paper. 



Summary of Results. 



Eontgen rays consist of two distinct undulations which 

 present themselves in succession. They are an irregular 

 progression of independent pulses in the first part of their 

 course — from the target upon which the kathode-rays impinge 

 up to the object which is being skiographed. Beyond that 

 object, between it and the fluorescent screen, they are a 

 different undulation. 



For, as proved in the June number of the Magazine, the 

 radiation from the target is the same physical (and not merely 

 kinematical) event as the simultaneous advance over the same 

 ground of trains of w r aves, some of long others of short wave- 

 lengths. Since the resolution into these trains of waves is 

 physical, the trains advance independently of one another; so 

 that if by any contrivance some of them can be stopped, the 

 rest will be unaffected and will proceed. Now the flesh of 

 the human hand is a contrivance of this kind : it is opaque 

 to the wave-lengths of all visible light and of much ultra- 

 violet light, but allows waves that are below a certain limit of 

 shortness to pass through it. Accordingly, the trains of suffi- 

 ciently short wave-lengths are the only physical constituents 

 of the first undulation which can get past this obstacle ; 

 and are what produce, by their coexistence in the space 

 beyond, that second part of the Eontgen undulation which 

 lies between the object and the fluorescent screen. 



Correction. 

 The numerical factors made use of on p. 535 of the June Magazine 

 should have been repeated a number of times that may be increased 

 without limit. Accordingly, the reader is requested to substitute the 

 following paragraphs, in which this omission is supplied, for the second 

 and two following paragraphs on that page. 



Next form the series of ascending prime numbers, viz.: — 

 2, 3, 5, 7, 11, 13, 17, 19, &c, 

 and call the continued product of the first n of these 



K 

 Phil. Mag. S. 5. Vol. 46. No. 279. Aug. 1898. T 



