434 THE POPULAR SCIENCE MONTHLY 



while the two possess the same charge, the inertia or mass which, so far 

 as we know, is inseparably associated with a positive nnit is that of a 

 Iwdrogen atom, while that inseparably associated with the negative unit 

 is 1/1, 760th as much. The negative units, furthermore, or electrons, 

 are so small in volume and are separated from one another within 

 the atom by so large spaces, that one of them can shoot through 

 hundreds and thousands of atoms without hitting anything or doing 

 anything whatever to these atoms. Its diameter is about one one- 

 hundred-thousandth of that of the atom. It is the smallest thing 

 we know anything about so far — probably the smallest thing in 

 existence. Such an enumeration of properties is as near to a definition 

 of electricity as we can come now or are ever likely to be able to come. 

 For, since electricity is the most fundamental thing thus far known to 

 us, it is obviously incapable of definition in terms of anything more 

 fundamental. Its elementary unit, according to the best determina- 

 tion which we have yet been able to make, is 4.80 times 10~^° so called 

 electrostatic units, a quantity so small that the electrical charge pro- 

 duced by a single stroke of a cat's back contains billions of them, while 

 the number which courses each second through the filament of a common 

 16 candle power incandescent lamp is about a billion billion. The 

 electron is thought by many reputable scientists of the present day to 

 be the primordial thing out of which all matter is built up, so that from 

 this point of view the different atoms of ordinary matter are merely 

 different groupings of these fundamental electrical units. 



Turning next to the kinetic theory of matter, what have the present 

 experiments to do with it ? There are three different ways in which they 

 bring to it powerful support. When these experiments were begun it 

 was anticipated that jjositively charged ions would be caught by nega- 

 tively charged oil drops and negatively charged ions by positively 

 charged oil drops, but it had not been predicted that positively 

 charged drops would catch positive ions and negatively charged drops 

 negative ions; for since electrical charges of like sign always repel each 

 other, it might be thought that positive drops would push away positive 

 ions and negative drops negative ions. As a matter of fact, however, 

 positive ions were found to be caught by positive drops about as readily 

 as the negative ions and vice versa. The above table shows several 

 catches of this kind. Whence, then, do positive ions obtain the energy 

 which enables them to push themselves up to the surface of a positive 

 drop against the electrical repulsion existing between the two? This 

 energy could not have been obtained from the field, since the capture of 

 the ions occurred when the field was not on. It could not have been 

 obtained from any explosive process which frees the electron from the 

 molecule at the instant of ionization, since in this case, too, ions would 

 have been caught as well, or nearly as well, when the field was on as when 



