104 MODERN THEORIES OF ELECTRICITY AND MATTER. 



to put the division of them beyond atoms and to admit the existence 

 of a kind of extremely small particles, able to enter into the com- 

 position of atoms, but not necessarily by their departure involving 

 atomic destruction. Looking at it in this light, we are led to con- 

 sider every atom as a complicated structure, and this supposition is 

 rendered probable by the complexity of the emission spectra which 

 characterize the different atoms. We have thus a conception suffi- 

 ciently exact of the atoms of negative electricity. 



It is not the same for positive electricity, for a great dissimilarity 

 appears to exist between the two "electricities. Positive electricity 

 appears always to be found in connection with material atoms, and 

 we have no reason, thus far, to believe that they can be separated. 

 Our knowledge relative to matter is also increased by an important 

 fact. A new property of matter has been discovered which has re- 

 ceived the name of radioactivity. Radioactivity is the property which 

 the atoms of certain substances possess of shooting oft' particles, some 

 of which have a mass comparable to that of the atoms themselves, 

 while the others are the electrons. This property, which uranium and 

 thorium possess in a slight degree, has led to the discovery of a new 

 chemical element, radium, whose radioactivity is very great. Among 

 the particles expelled by radium are some which are ejected with 

 great velocity, and their expulsion is accompanied with a consider- 

 able evolution of heat. A radioactive bod^' constitutes then, a source 

 of energy. 



According to the theory which best accounts for the phenomena 

 of radioactivity, a certain proportion of the atoms of a radioactive 

 body is transformed in a given time, with the production of atoms 

 of less atomic weight, and in some cases with the expulsion of elec- 

 trons. This is a theory of the transmutation of elements, but differs 

 from the dreams of the alchemists in that we declare ourselves, for 

 the present at least, unable to induce or influence the transmutation. 

 Certain facts go to show that radioactivity appertains in a slight 

 degree to all kinds of matter. It may be. therefore, that matter is 

 far from being as unchangeable or inert as it was formerly thought ; 

 ;ind is, on the contrary, in continual transformation, although this 

 transformation escapes our notice by its relative slowness. 



In the beginning of the last century Coulomb and Ampere 

 regarded each of the two kinds of electricity to be a fluid under tlie 

 influence of central forces — repulsion existing between particles of 

 the same fluid and attraction between particles of different fluids. 

 Such forces would be proportional in the electric charge of the par- 

 ticles, and would vary in inverse ratio to the square of the distance 

 between them. Starting with these hypotheses, and explaining 

 suitably the observed facts relative to the different nature of con- 

 ductors and dielectrics, they constructed a very perfect theory of 



