MODERN VIEWS ON MATTER. 291 



in accordance with what are called Faraday's laws; and in so far as 

 the mass of the atom itself is otherwise approximately known, the 

 quantity of electricity which can be associated with it is known with 

 a similar degree of approximate accuracy. 



3. Now mathematical data were given by J. J. Thomson in 1881 

 which enable us to say that if the charge of electricity usually asso- 

 ciated with a single monad atom of matter were concentrated on to 

 a spherical nucleus one-hundred-thousandth of an atom's dimension 

 in diameter, it would thereby possess a mass about one-thousandth of 

 that of the lightest atom known, viz., the hydrogen atom. 



Such a hypothetical concentrated unit of electricity it has become 

 customary to call an 'electron,' a name invented by Dr. Johnstone 

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

 electric charge. Every 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 which 

 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 nega- 

 tive 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 way; and each kind of matter possesses an intrinsic or char- 

 acteristic ionic velocity, when urged by 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 body which is dragged 

 along. The speed of travel through liquids 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 very many facts in both physics 

 and chemistry. 



