148 SOME OF THE LATEST ACHIEVEMENTS OF SCIENCE. 



elation several speakers, headed by Sir George Stokes, expressed their 

 conviction that the disturbed electric field caused by tho sudden stop- 

 page of the motion of an electrically-charged atom yielded the true 

 explanation of the phenomena extraneous to the Crookes high-vacuum 

 tubes — phenomena so excellently elaborated by Lenard and by Ront- 

 gen. More recently Sir George Stokes has restated his "pulse" 

 theory and fortified it with arguments which have an important bear- 

 ing on the whole theory of the refraction of light. He still liolds to 

 their essentially transverse nature in spite of the absence of polariza- 

 tion — an absence once more confirmed ))y the careful experiments of 

 Dr. L. Graetz. The details of this theory arc in process of elaboration 

 by Prof. J. J. Thomson. 



Meantime, while the general opinion of physicists seems to be settling 

 toward a wave or ether theory for the Rontgen rays, an opposite 

 drift is apparent with respect to the physical nature of the cathode 

 rays. It becomes more and more clear that cathode rays consist of 

 electrified atoms or ions in rapid progressive motion. My idea of a 

 fourth state of matter, propounded in 1881,^ and at first opposed at 

 home and abroad, is now becoming accepted. It is supported by Prof. 

 J. J. Thomson." Dr. Larmor's theory^ likewise involves the idea of 

 an ionic substratum of matter; the view is also confirmed by Zeeman's 

 phenomenon. In Germany — where the term cathode rays was invented 

 almost as a protest against the theory of molecular streams propounded 

 l)y me at the Sheffield meeting of the British association in 1879 — 

 additional proofs have been produced in favor of the doctrine that the 

 essential fact in the phenomenon is electrified radiant matter. 



The speed of these molecular streams has been approximately 

 measured, chiefly by aid of my own discover}" nearh^ twenty years 

 ago, that their path is curved in a magnetic field, and that they pro- 

 duce phosphorescence where they impinge on an obstacle. The two 

 unknown quantities, the charge and the speed of each atom, are 

 measurable from the amount of curvature and })y means of one other 

 independent experiment. 



It can not be said that a complete and conclusive theor}^ of these rays 

 has yet been formulated. It is generally accepted that collisions 

 among particles, especiall}^ the violent collisions due to their impact 

 on a massive target placed in their path, give rise to the interesting 

 , kind of extremely high frequency radiation discovered by Rontgen. 

 It has, indeed, for some time been known that, whereas a charged body 

 in motion constitutes an electric current, the sudden stoppage, or any 

 violent acceleration of such a body, must cause an alternating electric 

 disturbance, which, though so rapidly decaying in intensit}" as to be 

 practically "dead beat," yet must give rise to an ethereal wave or pulse 



iPhil. Trans., part 2, 1881, pp. 433-434. »Phil. Mag., December, 1897, p. 506. 



2 Phil. Mag., October, 1897, p. 312. 



