MODEEN VIEWS ON MATTER. 217 



Such a h3"pothetical concentrated unit of electricity it has become 

 customary to call an ''electron,'"' a name invented by Dr. Johnstoi.e 

 Stoney to designate the so-to-speak "atom" or smallest known unit of 

 electric charge. Eyery electric charge is to be thought of as due to 

 the possession of a number of electrons, but a fraction of an electron 

 is at present considered impossible, meaning that no indication of any 

 further subdivision has ever loomed even indistinctly above the 

 horizon of practical or theoretical possibility. 



The electrification of an atom of matter consists in attaching such 

 an electron to it or in detaching one from it. An atom of matter 

 possessing an electron in excess is called an "ion;" and there is reason 

 to know that, considered as a charged body, its charge is that Avhich 

 we have been historically accustomed to designate ' ' negative ;" whereas 

 an atom of matter with one electron in defect is that which has his- 

 torically been called a "positive" ion. 



This inversion in the natural use of the names positive and negative 

 is inconvenient but accidental and not really serious; it dates from the 

 time of Benjamin Franklin. 



These ions or traveling particles of matter have been long known. 

 A liquid or a gas conducts because of the locomotion of its charged 

 particles. The particles travel in an electric field because of their 

 attached charges, all the positive going one way, and all the negative 

 the other wa}^; and each kind of matter possesses an intrinsic or char- 

 acteristic ionic velocity, when urged b}' a given field through a given 

 solution. The charges may be likened to horses or other propelling- 

 agency, and the atom to the vehicle or heavy bod}" which is dragged 

 along. The speed of travel through li(|uids is very slow, but through 

 gases is considerably quicker, partly because there is less resistance, 

 and partly because it is easier to maintain a steep gradient of potential 

 in a medium where the ions are not too numerous. 



The act of production of such ions is styled "ionization," and the 

 process has been employed to explain ver}- many facts in both phj^sics 

 and chemistry. 



As an example, Rontgen rays passing through air ionize it and 

 so render it conducting for a time; wherefore they arc able readil}' to 

 discharge electrified bodies in this secondary way. 



It may be convenient here to emphasize the dimensions of an electron 

 as above specified, for the arguments in favor of that size are ver}^ 

 strong, though not absoluteh" conclusive; we are sure that their mass 

 is of the order one thousandth of the atomic mass of hydrogen, and 

 we are sure that if they are pui'ely and solely electrical their size must 

 be one hundred-thousandth of the linear dimensions of an atom; a size 

 with which their penetrating power and other behavior is quite con- 

 sistent. Assuming this estimate to be true, it is noteworthy how very 

 small these electrical particles are, compared with the atom of matter 



