PHYSICS 329 



electric charge. These processions are always double, the atomic 

 carriers of the positive charge moving in one direction, those carrying 

 the negative charge in the other. The same quantity of positive elec- 

 tricity is carried by one procession, as negative electricity by the other. 

 We have not only measured the charge carried by a single atom, but the 

 average speed with which the atoms traverse the solution. It has been 

 found, further, that atoms of the different chemical elements having the 

 same mating value, technically called valence, always carry the same 

 unvarying charge, whether the atoms themselves be light or heavy. 

 These charged atoms, in some cases atom groups, are spoken of as ions. 



Such electrolytic experiments as these have led to two surprising 

 results. First : no electric charge smaller than that carried by an atom 

 of the hydrogen valence has yet been found. Second : all other small 

 charges are exact multiples of this value. 



We have long been familiar with the idea of atoms of matter, but 

 here for the first time we come across something which looks very like 

 an atom, or natural unit, of electricity. The justification for calling it 

 an atom of electricity is like the argument for the atom of matter. 

 Moreover, we know some eighty different kinds of material atoms, but 

 only two kinds of electric atoms, a positive and a negative. Thus the 

 electric atom of the two has the greater claim to simplicity. When we 

 speak of an electric atom disregarding for the time the matter asso- 

 ciated with it, we call it, not an ion, but an electron. Evidence will 

 later be given suggesting ways by which we may wrench a negative 

 electron wholly free from matter, and experiment with it in its detached 

 and pure state. 



We are now in a position to consider the role electric forces play in 

 holding atoms together within a compound molecule, for, from the 

 foregoing, it appears when a molecule is broken in two, the fragments 

 are always found equally and oppositely charged, and they doubtless 

 held these charges within the molecule. But the distance separating 

 the two parts was then so small that all the lines of force from the 

 positive charge ended at once on the equal negative charge, and no 

 force lines strayed beyond the molecular boundary. Hence no evidence 

 of an electrical charge could be found in the ether outside the molecule. 

 It seems probable, therefore, that the electric force between the atoms 

 of matter in the molecule supplies the chemist with the cement he has 

 long called chemical affinity. 



The ratio of the electric charge to the mass of the particle on which 

 it rides (in our processions) has come to be one of the most important 

 quantities in physics. As we know both the quantity of matter and 

 quantity of electricity transferred by a given electric current, we can 

 express this ratio for each chemical element. Hydrogen gives the 

 largest ratio found in solutions. 



Systematic study of the conduction of electricity in gases is of more 



