238 MODERisr VIEWS ()]sr matter. 



almost completely tirrested l)y tli(> thinnest sheet of matter, electrons 

 will pass almost uno])structed throuo'h ordinary opaque bodies. 



The action of these emanations on phosphorescent screens is differ- 

 ent. The electrons strongly affect a screen of barium platinocyanide, 

 but onl}' slightly one of Sidot's zinc sulphide. On the other hand, 

 the heavy, massive, nondeflectable positive ions affect the zinc-s'ilphide 

 screen strongly, and the barium-piatinocyanide screen in a much less 

 degree. 



Both KcHitgen rays and electrons act on a photographic plate and 

 produc(^ images of metal and other substances inclosed in wood and 

 leather, and thi'ow shadows of bodies on a barium-piatinocyanide 

 screen. Electi'ons are much less penetrating than Rontgen rays, and 

 will not, for instance, show easily the bones of the hand. A photo- 

 graph of a closed case of instruments is taken by radium emanations 

 in thi-ee days and by Rontgen rays in three minutes. The resemblance 

 between the two pictures is slight and the dilferences great. 



The power with which radium emanations are endowed of discharg- 

 ing electriiied bodies is due to the ionizatioji of the gas through which 

 they pass. This can be effected' in many other w^ays; thus, ionization 

 is communicated to gases faintly 1)V the splashing of water, by ffames 

 and red-hot bodies, ])v ultraviolet light falling on negatively electri- 

 ffed metals, and strongly l)y the passage of Rontgen rays. 



According to Sir Oliver Lodge's electronictheory of matter, a chem- 

 ical atom or ion has a few extra negative electrons in addition to the 

 ordinary neutral atom, and if these negative electrons are removed it 

 there!)}" becomes positively charged. The free electron portion of 

 the atom is. small in comparison with the main bulk, in the proportion 

 in hydrogen of al)Out 1 to 7W. The negative charge consists of super- 

 added or unbalanced electrons — one, two, three, etc., according to 

 the chemical valenc}" of the body — whereas the main bulk of the atom 

 consists of paired groups, equal 2:)Ositive and negative. As soon as 

 the excess electrons are removed the rest of the atom, or ion, acts as 

 a massive positively charged body hanging tightly together. In a 

 high vacuum the induction spark tears the components of a rarified 

 gas apart; the positively charged ions, having great comparative 

 density, are soon slowed down by collisions, while the electrons are 

 driven from the negative pole with an enormous velocity, depending 

 on the initial electromotive force and the pressure of gas inside the 

 tube, but approaching at the highest exhaustions half that of light. 



After leaving the negative pole the electrons meet with a certain 

 resistance in a slight degree l)v physical collisions, but principall}^ by 

 reunion with the positive ions. 



Since the discovery of radium and the identiiication of one set of its 

 emanations with the cathode stream or radiant matter of the vacuum 

 tube, speculation and experiment hav<» gone hand in hand, and the 



