272 MODERN SCIENCE READER 



ing them, recent theories relative to electricity and to 

 matter. 



But though radioactivity is in close relation to physics 

 and chemistry above all, it is not foreign to other domains 

 of science, and in these acquires increasing importance. 



Radioactive phenomena are so varied, their manifesta- 

 tions are so diverse and so widespread in the universe, that 

 they should be taken into consideration in the study of the 

 natural sciences, especially in physiology and therapeutics, 

 in meteorology and geology. 



Many laboratories actually devote themselves to the study 

 of radioactivity. Institutes are being created for the cen- 

 tralization of relatively important quantities of radium, 

 the principal instrument of research in this new domain. 

 And by reason of these efforts the importance of the subject 

 must still further increase. 



I published in 1903 a small volume entitled Researches 

 Upon the Radioactive Substances, in which was reviewed 

 the state of the subject at that period. In 1905 appeared 

 the excellent treatise of Professor Rutherford, which has 

 had a more complete recent edition and has rendered great 

 service. 



In the present work I have tried to give an exposition as 

 complete as possible of the phenomena of radioactivity, in 

 the actual state of our present knowledge. 



The plan of my first book has been preserved in part, but 

 the work comprises a much more ample field, corresponding 



to the sudden development of the science. 



******** 



Radioactivity is a new property of matter which has been 

 observed in certain substances. Nothing warrants us in 

 actually affirming that this is a general property of matter, 

 though this opinion presents nothing a priori impossible, 

 and may even seem quite natural. 



Radioactive bodies are sources of energy whose disen- 

 gagement manifests itself by diverse effects: the emission 

 of radiations, of heat, of light, of electricity. 



