218 MODERN VIEWS ON MATTER. 



to vvliicli tlicv are attached. If an electron is represented by a sphere 

 an inch in diameter, the diameter of an atom of matter on the same 

 scale is a mile and a half. Or if an atom of matter is represented by 

 the size of this theater, an electron is represented on th^ same scale 

 by a printer's full stop. It is well to bear this extreme smallness in 

 mind in what follows. 



An atom is not a large thing, but if it is composed of electrons, the 

 spaces between them are enormous compared with their size — as great 

 relative!}^ as are the spaces between the planets in the solar system. 



4. My next thesis is that these electrons or minute-charged cor- 

 puscles can exist separately, for they can l)e detached from their atoms 

 of matter at an electrode, not only in electrolytic liquids but also in 

 gases, and when thus released from their thousandfold more massive 

 atom, they flj^ away from the negative electrode with prodigious speed, 

 because they are acted on by the same electrical propelling force as 

 before, but now have hardly anything to move. 



These isolated flying particles travel a long distance in rarefied 

 gas, and are known as cathode rays. They were studied by Hittorf, 

 Crookes, Lenard and others, both inside and outside vacuum tubes, 

 and they are now known to be flung ofl' spontaneously from many 

 substances. When stopped suddenly by a massive obstacle, they give 

 rise to the X radiation discovered by Rontgen. At first these cathode 

 rays were thought to be atoms of matter, though their extraordinar}^ 

 penetrating power rendered such a hypothesis diflicult of belief, and 

 caused Crookes to speak of them as matter in a fourth state. They 

 are, however, certainly energetic bodies, being abfe to propel light 

 windmills, to heat platinum to redness, and to charge an electroscope; 

 they are also able to penetrate thin sheets of metal and to affect pho- 

 tographic plates or phosphorescent substances on the other side. They 

 are not so penetrating, however, as are some of the Rontgen rays. 



The final definite establishment of the fact that these flying par- 

 ticles are not atoms of matter, ])ut are bits chipped off the atoms, frac- 

 tions of an atom, as it were, the same identical kind of bits being- 

 chipped off every kind of chemical atom, their mass always about one- 

 thousandth of that of a hydrogen atom, and moving under favorable 

 circumstances with something not much less than the speed of light, is 

 due to the researches of Prof. J. J. Thomson and his coadjutors in the 

 Cavendish Laboratory, Cambridge, and represents a long series of 

 measurements devised and executed with consummate skill. 

 ■ I have no time to go into detail concerning these important and 

 elaborate and most interesting investigations. Suffice it to say that 

 portions of them are due to your own Wykeham professor of physics, 

 Professor Townsend, working in conjunction and collaboration with 

 others, under the leadership of Prof. J. J. Thomson; and that this 

 whole series of Cavendish Laboratory researches may be said to con- 



