INAUGURAL ADDRESS. ZO 



interfering with the motion of the negative. The effect was not an- 

 ticipated on the pulse theoiy. It is now proposed to modify that 

 theoiy, so as to explain a certain amoimt of dissjaiimetry, but it seems 

 to me that it will be very difficult to explain the completely unidirec- 

 tional movement of the beta ray. On the whole, therefore, it seems 

 proper to class the gamma and the Rontgen rays with the alpha and 

 beta, the nature of which is more certain ; and to ascribe a material 

 character to them all. In this way they would stand entirely differen- 

 tiated from the radiations which we call light and heat ; and the 

 absolute dift'erence in the i)roperties of the two classes of radiation 

 woidd imply an absolute dift'erence in their natures. In one we should 

 see the travelling to and fro through space of those aether waves 

 which we have been investigating for centuries ; in the other a con- 

 tinuous dance of atomic particles. Just as the theory of gases teaches 

 us to think of the gaseous molecules moving rapidly from collision to 

 collision with each other, and the seemingly quiet air to be the seat 

 of the most vivid movement, so the lessons of radio-activity show us 

 a, continuous movement far finer still in which the parts of atoms torn 

 from their normal places tly about at inconceivable speeds encounter- 

 ing only each other. Though there is a strong family likeness Ijetween 

 all in their properties, yet there is also a most interesting variety in 

 their natures and histories. Some may be set in motion in the vacuum 

 tube under the action of electric forces, but the alpha, the beta, and 

 the gamma rays arise from the disintegration of the atom. Certain 

 forms are interchangeable as we have seen. The life of each ray is 

 veiy short, and it may be that as the appearance of the ray is the 

 sign of an atomic breakdown, so in some cases the disappearance is 

 really contributory to atomic growth. Some of the rays as they move 

 through a gas cause the aj^pcarance of delta rays, and throw the gas 

 for a time into a state of '' ionisation." 



If we now ask to Avhat extent tliis radiation exists, whether, for 

 example, it is prevalent and influential enough to aft'ect the events of 

 our existence, it is not easy to give a satisfactory answer at present. 

 Of the great scientific importance of our new knowledge there can be 

 Tio doubt; of the magnitude of the part which it plays in the working 

 ■of the universe our knowledge is insufficient as yet. We can see 

 importance enough in a science which deals with the evolution and 

 destruction of the atoms of which all materials are made. We can 

 ^rasp the significance of the fact that r^io-active material exists in 

 our earth and air in sufficient quantities to have great influence on the 

 temperature of the globe and on the electric state of the atmosphere. 

 But it also seems likely that in a thousand waj's yet unsuspected tlie 



