182 J. MORISON : ADDRESS 



substance. They are bent by a magnet. They consist of 

 negatively electrified particles, each about -ru'co part the size of 

 a hydrogen atom, and they move with the velocity of 20,000 to 

 60,000 miles a second. In fact, they are in every respect 

 identical with the negative ions or corpuscles mentioned before. 

 When these rays of corpuscles are suddenly arrested, either by 

 impinging on the glass of the tube, or still more effectively by 

 striking a metal plate, they give rise to the well-known X or 

 Rontgen rays, which are not corpuscular, but are due to peculiar 

 vibrations or pulses in the ether. The Eontgen rays have 

 a remarkable power of penetrating solid matter which is opaque 

 to ordinary light. 



We get positive rays also from the anode or positive electrode. 

 They are much fainter and more inconspicuous than the cathode 

 rays, and move comparatively slowly. They have been called 

 the anode or canal rays. They are slightly deflected by a 

 magnet in the opposite direction to the cathode rays. They 

 consist of positively electrified particles, and are of atomic 

 dimensions, comparable in size to an atom of hydrogen or 

 helium. These positive ions are not all exactly similar to each 

 other, like the negative ions or corpuscles, but vary to some 

 extent according to the source from which they are derived. 

 J. J. Thomson considers that they are " atoms or groups of 

 atoms from which one or more corpuscles have been removed." 



Corpuscles or negative ions are produced under many different 

 conditions. All substances which are heated evolve them to some 

 extent. Wlaen metals and some other substances are exposed to 

 light, corpuscles are emitted. We can detect their emission from 

 some substances, such as lithium and an alloy of potassium and 

 sodium, even when cold. And there is reason to suppose that all 

 substances emit them to some extent. Corpuscles are produced 

 in large quantities when salts are put into flame. They are 

 continually being formed in very great numbers and emitted 

 with very great velocities by certain bodies which are called 

 radio-active. And according to J. J. Thomson there is good 

 reason to suppose that corpuscles reach us from the sun. Their 

 distribution is therefore very wide, and they appear to form part 

 of all kinds of matter under all sorts of conditions. From 

 whatever source they may be derived, they seem to be always 

 exactly similar to each other. 



Now let us deal with radio-activity and radio-active bodies. 



When the X rays were discovered in 1896 it was at first 

 supposed that the luminescence or phosphorescence of the glass 



