300 Sir Jamen Mackenzie Davidson [Feb- 2, 



helinm was one of its products. This discovery may be looked upon 

 as the first actual proof of the transmutation of elements. Chemists 

 had long l»een familiar with the energy evolved by the rearrangement 

 of molecules, such, for example, as in the explosion of dynamite, Imt 

 the enormous energy evolved l>y the disintegrating atom was found 

 to be almost incredilile. There is, however, this marked difference, 

 that while we have control over the molecular combinations, we have 

 no control whatever over the disintegration of the atom, which is a 

 purely spontaneous action. This disintegration proceeds at the 

 highest temperatures exactly in the same way as has been proved to be 

 the case in the lowest temperatures. The beautiful researches of Sir 

 J. J. Thomson have helped us to realise that an atom consists of a 

 large number of corpuscles. Soddy has stated that the amount of 

 heat evolved by any quantity of radium every hour is just about as 

 much as is required to raise an amount of water equal in weight to 

 the radium from the freezing-point to the boiling-point. The quan- 

 tity of radium obtainable is so small, being only one part in five 

 millions of the Ijest pitchblende, that it has never beeen experimented 

 with as a drug in the ordinary sense to any extent, and its biological 

 properties in this respect are consequently unknown. 



It is the radiant energy evolved by the disintegration of the radium 

 atom which is of value to us in medicine. The average life of radium 

 is 25U0 years, so that anyone who buys radium can have no personal 

 anxiety about its lasting qualities. So far as we are concerned this 

 evening we have to consider the three rays, called Alpha, Beta and 

 Gamma rays, which radium gives off. 



In the process of flying to pieces, or disintegration, the radium 

 atom first gives off an atom of helium, at a velocity of about twenty 

 thousand miles per second. This is called the alpha ray, which is 

 beautifully demonstrated by a little instrument devised by Sir William 



[Show spinthariscope.] 



Crookes and called the spinthariscope. The remainder of the atom 

 evolves as a gas or " emanation." The emanation in its turn decom- 

 poses, losing half its energy in about four days, and finally gives rise 

 to an active deposit of rapid change. In its turn also this deposit 

 gives off alpha, beta and gamma rays, and these are the three kinds 

 of rays, together with the emanation, which are of importance in the 

 consideration of the vital effects of radium. It is very probable that 

 the ultimate product of this disentegration is lead. 



Alpha Rays. — The alpha ray, as already mentioned, consists of an 

 atom of hehum travelling with a comparatively small velocity. It 

 lias a very feeble power of penetration, being stopped by two or three 

 centimetres of air, while a sheet of paper will suffice to prevent it 

 from issuing. The action of the alpha rays on living ceUs is uncertain. 



