292 POPULAR SCIENCE MONTHLY. 



As an example, Eontgen rays passing through air ionize it and 

 so render it conducting for a time: wherefore they are able readily 

 to discharge electrified bodies, in this secondary way. 



It may be convenient here to emphasize the dimensions of an 

 electron as above specified, for the arguments in favor of that size are 

 very strong, though not absolutely conclusive; we are sure that their 

 mass is of the order one thousandth of the atomic mass of hydrogen, 

 and we are sure that if they are purely and solely electrical their size 

 must be one hundred-thousandth of the linear dimensions of an atom; 

 a size with which their penetrating power and other behavior is quite 

 consistent. Assuming this estimate to be true, it is noteworthy how 

 very small these electrical particles are, compared with the atom of 

 matter to which they 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 rep- 

 resented by the size of this theater, an electron is represented on the 

 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 

 relatively 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 be 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 fly 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 off 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 extraordinary 

 penetrating power rendered such a hypothesis difficult of belief, and 

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

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

 windmills, to heat platinum to redness, and to charge an electro- 

 scope; they are also able to penetrate thin sheets of metal and to 

 affect photographic plates or phosphorescent substances on the other 

 side. They are not so penetrating, however, as are some of the 

 Eontgen rays. 



