600 Mr. Alan A. CampbeU Sivinton [Feb. 4, 



of a single transverse wave or ripple, but the pulses following one 

 another in no regular order, or at any regular frequency as do the 

 trains of vibration of ordinary light. 



Then again, there is the question of the mechanism by means of 

 which the Routgen rays are produced. They are generated by the 

 impact of the cathode rays upon the anti-cathode, and it is now 

 becoming more and more certain that the cithode rays consist of 

 negatively charge! at)ms travelling at enormous velocity. If we 

 accept this view, tliere are obvii;usly several methods by which we 

 may imagine the Eontgen rays being generated by the impact of the 

 travelling atoms upon the anti-cathode. Each cathode ray at(mi 

 carries a negative charge, while the anti-cathode is positively charged, 

 so that when the two come into contact an electrical discharge will 

 take place between tliem. An electrical oscillation will thus take 

 l^lace in the atom just as in the brass balls of a Hertz oscillator, and 

 transverse electro-mnguetic waves will be propagated through the 

 ether in all available directions. As the electro-static capacity of 

 the atom must be exceedingly small, the periodicity of oscillation 

 and the wave frequently will be enormous, while at the same time 

 the oscillation will probably die out with sufficient rapidity to admit 

 of only one or two corai)lete periods. At the same time the greater 

 the difference of potential between atom and anti-cathode at the 

 moment of impact the greater will be tha amplitude of oscillation, 

 and the more vigorous and far-reaching the etheric disturbances. 



Or we may imagine a more purely mechanical origin for the 

 Eoutf'en rays. It is believed that tlie velocity of the cathode rays 

 is enormous, being, as recently measured by J. J. Thomson, over 

 10,000 kilometres per second, and though Lodge, in his well-known 

 endeavours to detect a movement of the etlier by dragging a material 

 body through it, obtained only negative results, of course he could not 

 i)ossibly obtain any velocity at all comparable to this. Assuming that 

 at the velocity of the cathode ray atoms these do appreciably drag the 

 ether with them, there may be some ether effect produced analogous 

 to the atmospheric effect that is noted as the crack of a whip or a 

 clap of the hands, as each atom hits the anti-cathode and rebounds.* 



Or agiin, it is conceivable that the phenomenon is merely one 

 of heating, and that the cathode ray atoms are by impact with the 

 anti-cathode raised to such an enormous temperature that they give 

 off for a short space of time supor-ultra-violet light. Taking a 

 velocity for the atoms of 10^ centimetres per secon i, as found by 

 J. J. Thomson to be the minimum velocity of the cathode rays, and 

 calculating the temper i^^ure to which a nitrogen atom would be raised 

 if, when travelling at this speed, it w^ere instantly brought to rest 



* Since the above was written, Ihe writer's attention lias been drawn to 

 Professor J. J. Tliomsou's paper, " A Theoi y of tlie Connection between Cathode 

 andRoiitgen Rays," in the 'Philosophif-al Magazine 'for February, ia which it is 

 suggested that Rontgen rays consist of very tliin ami intense tlectro-niagnetic 

 pulses produced in the etlier by the sudden stoppage by the anti-cathode of the 

 ekctiifled particles of the cathode rays. 



