1898.] on Some New Studies in Cathode and Rontgen Badiafions. 599 



at one of the two points of greatest curvature of each ellipse, the 

 Hontgon rays are produced more actively than in the remaining 

 portion, where the cathode rays impinge on the anti-cathode more on 

 the slant. This is still more marked in Fig. 2i, which shows what 

 are practically sectiims through the major and minor axes of one of 

 the images shown in Fig. 28. They were taken similarly to the 

 others, b:;t with the pin-hole and photographic plate almost in the 

 j)lane of the antl-cathodc. 



By some it is imagined that because the Rontgen rays are so very 

 penetrating, therefore they are of the nature of an invisible light of 

 great intensity, which though not affecting the human retina acts 

 upon photograpliic })lates very powerfully. This is quite erronous, 

 and as a matter of fact the photographic effect of Kontgen rays is 

 relatively very feeble. I have investigated this by means of two 

 photograpliic plates which I have exposed respectively to a very 

 powerfully excited l^ontgen ray tube, screened by black paper to 

 remove the visible luminosity, and to the light of a single standard 

 candle. The Rontgen ray tube was employed at a distance of two 

 feet, and the candle at a distance of ten feet, so that according to the 

 law of inverse squares, which holds good for Rontgen rays as for 

 light, tlie intensities of the two radiations, supposing them to be 

 equal to start with, would be in the projiortion of 25 to 1. Each 

 p^ate was exposed in sections for varying lengths of time, five, ten, 

 fifteen seconds, and so on, each succeeding section being exposed 

 live seconds longer than the preceding one. By sliding tho two nega- 

 tives past one another it is possible to compare them very accurately, 

 and the section exposed to the light of the standard candle for ten 

 seconds is almost exactly of equal density to the section exposed 

 to the Rontgen rays for twenty-five seconds. The photographic 

 power of this particular Rontgen ray tube — and it was a very good one 

 — was therefoe less than one-sixtieth of that of one standard candle. 



With regard to the true nature of the Rontgen rays there have 

 been many theories. There is the original suggestion of Rontgen 

 himself, that they may possibly consist of longitudinal waves in the 

 ether. Others have thought that they were possibly ether streams or 

 vortices. There is a theory propounded by Tesla and others that 

 they consist of moving material particles, atoms or corpuscles, 

 similar to the cathode ruys, which reminds one of Newton's corpus- 

 cular theory of light. There is the more generally received doctrine 

 that they are simply exceedingly short transverse ether waves similar 

 in all respects to the waves of light, only so much shorter than tlie 

 most ultra-violet waves hitherto known that they pass between the 

 molecules of matter, and are consequently neither refracted nor easily 

 absorbed or reflected by any media. Lastly, there is the theory first 

 suggested to the writer early in 1896 by Professor George Forbes, 

 and recently independently enunciated and elaborated by Sir George 

 Stokes, v;liich imagines them to bo frequently but irregularly repeated, 

 isolated, and indbpendent disturbances or jnilses of the ether, each 

 pulse being similar 2)erha2)S to a single wave of light, and consisting 



2 R 2 



