112 MODERN THEORIES OF ELECTRICITY AND MATTER. 



Ingenious experiments have made it possible to count the globules 

 present in a cubic centimeter of cloud and thus to obtain the number 

 of ions present in this volume. By measuring, in addition, the total 

 charge of the ions of each sign in a cubic centimeter the individual 

 charge of the ions is determined — that is to say, the charge of a single 

 atom of electricity. This charge is equal to 3.4 times 10-^" electro- 

 static units. In order to show this phenomenon the gas may be 

 ionized by the introduction of a glowing platinum wire, and it will 

 be recognized that there is an energetic ionization of the gas sur- 

 rounding the incandescent body. 



We will now pass to the essential facts revealed by the study of 

 radio-active substances, and examine them from the point of view of 

 the hypothesis of the atomic transformation of matter. Among 

 the radioactive elements, some appear to be permanently active 

 (uranium, thorium, radium, actinium) while others lose their radio- 

 activity little by little (polonium). The most powerful representa- 

 tive of the permanently radioactive substances is radium. Accord- 

 ing to the theory of transformation this substance changes very 

 slowly, so that a given mass of radium would lose half its weight 

 only in several thousand years. Consequently the quantity of radimn 

 which disappears from a gram of this substance in an hour is 

 absolutely inaccessible to experiments. However, a gram of radium 

 disengages each hour about 100 calories of heat. To conceive how 

 enormous this disengagement of heat is, we remark that during the 

 life attributable to radium the complete transformation of a gram of 

 this substance would produce as much heat as the combustion of a 

 ton of coal. The transformation of radium, then, if transformation 

 there be, is not to be regarded as an ordinary chemical reaction, for 

 the quantity of heat involved is of a far higher order. One is led to 

 conceive, rather, that the atoms themselves are transformed, for the 

 quantities of energy j^ut in play in the formation of atoms are 

 probably considerable. 



Indeed, the phenomena of radioactivity has a palpably atomic 

 character which was brought to light in the beginning of researches 

 on the subject. It was precisely the absolute conviction that we were 

 dealing with an atomic phenomenon which led M. Curie and me to 

 the discovery of radium. If the radioactivity can not be separated 

 from the atom it is very difficult to conceive anything but the atom 

 itself involved in the transformation. 



The effects produced by radium are very powerful considering 

 how small is the quantity of this substance at disposal for experi- 

 ments. There is a spontaneous and continuous emission of rays, 

 analogous to those which w^e know are produced by means of an 

 induction coil in a Crookes tube, and these rays produce ionization 

 of gas in the same manner. They are able, for example, to produce 



