16 CONTEMPORARY SCIENCE 



metical series ; that is, which will come up by steps, one, 

 two, three, etc. That is exactly what we found. We 

 have experimented with thousands of drops and scores of 

 different substances, and they always work exactly that 

 way. Both positively and negatively charged drops are 

 found to act in quite the same way, showing that both 

 positive and negative electrical charges are built up of 

 specks of electricity. Further we can count the number 

 of those specks, which we will call electrons, in a given 

 drop, with the same certainty with which you can count 

 the number of fingers that are on your hand. And 

 again since Rowland showed that an electrical current is 

 nothing but a charge in motion, you have here the proof 

 that the electrical current that goes through these lamps, 

 for example, is nothing except the motion of a certain 

 number of electrical specks through or over the filament 

 of the lamp. Add to that J. J. Thomson's discovery made 

 in 1881, that an electrical charge possesses inertia, the 

 only distinguishing property of matter, and you have made 

 it perfectly legitimate to say that an electrical current in 

 a wire is a definite, material, granular something which 

 is moving along that wire. 



The fifth great discovery of modern physics is the. bring- 

 ing forward of evidence for the electrical origin of mass. 

 I have just said that electricity is material. Can we turn 

 it around, and say that all matter is electrical in origin? 

 The last is not exactly the same as the first, and it needs 

 evidence. When we have proved that an electrical charge 

 possesses inertia or mass we have not shown that there is 

 no inertia in matter which is not electrical in its origin. 

 Now we have a certain amount of evidence upon this point 

 and I wish to state what that evidence is. We can meas- 

 ure the inertia of the negative electron and it is found to 

 be one-one thousand eight hundred and forty-fifth part of 

 the inertia of a hydrogen atom, but the positive electron is 

 never found with an inertia less than the inertia of a hy- 

 drogen atom. Let us consider the inertia of the negative. 



