THE BECQUEREL RAYS 1 



IT is remarkable how the writings of ancient authors often 

 contain a forecast of subsequent discoveries. Puck's pro- 

 jected girdle round the earth, which was promised com- 

 pletion in forty minutes, has been surpassed many hundred 

 times by the rate of the electric current in a telegraph- 

 wire ; and Robert Boyle's suggestions regarding the nature 

 of the air are on the high-road towards verification. He 

 wrote, about the year 1670: 'Our atmosphere, in my 

 opinion, consists not wholly of purer aether, or subtile 

 matter which is diffused thro' the universe, but in 

 great number of numberless exhalations of the terr- 

 aqueous globe; and the various materials which go to 

 compose it, with perhaps some substantial emanations from 

 the celestial bodies, make up together, not a bare indeter- 

 mined feculancy, but a confused aggregate of different 

 effluvia.' 



Up to 1894, it was supposed that our atmosphere con- 

 sisted mainly of the two gases, nitrogen and oxygen, together 

 with minute quantities of carbonic acid, water- vapour, 

 ammonia, peroxide of hydrogen, and ozone ; but in that 

 year it was shown to contain a not inconsiderable amount 

 of an inactive gas, argon ; and crude argon has since been 

 found to contain minute quantities of no fewer than four 

 other similar gases. Small traces of hydrogen have also 

 been discovered in air; although a large percentage of 



1 An article which appeared in the Contemporary Review, 1902. 



I 



