WHAT IS ELECTRICITY? — HEYL 



223 



We have now brought this somewhat hurried survey of electrical 

 history up to the present day. We have seen that past speculations 

 as to the nature of electricity fall into four classes, each correspond- 

 ing to an era of thought. In the first of these eras, beginning prob- 

 ably with the earliest observations of electrical attraction, and 

 terminating in the middle of the sixteenth century, electricity was 

 regarded as a soul or spirit. The second era may be said to have 

 been opened by Cardan in 1551 and closed by Maxwell in 18G5. Dur- 

 ing these three centuries electricity was regarded as a material fluid 

 of one or two kinds. It is worthy of note that during this period 

 the concept of the electrical fluid showed a trend toward the imma- 

 terial, from Cardan's " fatty and glutinous humor " to the impalpable 

 and imponderable fluid of the early nineteenth century. In the 

 third era electricity in its various manifestations was regarded as 

 some kind of an ether disturbance of a continuous nature. The 

 fourth concept emphasized the atomic or discontinuous structure of 

 electricity without any suggestion as to the ultimate nature of these 

 atoms. 



But though speculation as to the ultimate nature of electricity has 

 been in abeyance since the opening of the twentieth century, it will 

 certainly arise again, and, within limits, it is well that it should. We 

 may, therefore, turn now to an examination of the wealth of material 

 which the last 40 years have placed at our disposal and see what it 

 may contain that is likely to be of importance in guiding and sug- 

 gesting future speculation as to the nature of electricity. 



The emphasis laid by the twentieth century on the structure, 

 rather than the nature, of electricity is natural, for structure is much 

 more easily determined than nature, and, moreover, a knowledge of 

 the first is likely to give us some useful hints as to the second. It 

 appears that the discontinuous structure of electricity goes almost 

 hand in hand with that of matter. A tabular view of the known 

 elementary particles of matter with their associated charges of 

 electricity will be useful. 



Charge 



Mass: Heavy. 

 Mass: LiRht.. 



Proton 



+Electron 



-Electron 



Neutron 

 (Neutrino) 



The heavy particles now known, the proton and the neutron, have 

 a mass equal to that of a hydrogen atom; the light particles have 

 about 1/1800 of this mass. The light neutral particle has not yet 

 been discovered, but so urgent is the demand for it in current nuclear 

 theory that it has been named before its advent. 



