1920] Thermionic Valve in Wireless Telegraphy & Telephony 163 



Another fact I observed very soon was, that the filament was 

 giving off torrents of negative electricity, and could discharge a 

 positively electrified conductor connected to the plate, but not a 

 negatively charged one. 



This is easily shown by connecting a gold leaf electroscope to the 

 collecting plate, and charging it alternately with negative and with 

 positive electricity when the filament is not alight. On making the 

 filament incandescent it instantly discharges the positively charged 

 electroscope, but not if it is negatively electrified. Furthermore, I 

 found that the vacuo as space between the filament and the plate 

 possessed a curious unilateral electric conductivity for low voltage 

 direct electric currents, and that even a single cell of a battery could 

 pass a current from the hot filament to the collecting plate if the 

 negative pole of the battery was in connection with the hot filament, 

 but not in the opposite direction. This fact had, however, been 

 previously noticed in another manner by W. Hittorf. These experi- 

 ments were made in 1888 or 1889, and at that time were not 

 satisfactorily explained. 



It was not until nearly ten years later that your distinguished 

 Professor of Natural Philosophy, Sir Joseph Thomson, published 

 accounts of his epoch-making and important researches in which he 

 proved that the agency we call negative electricity is atomic in 

 structure, and exists in indivisible units now named electrons, which 

 carry a certain electric charge and have a certain mass. This small 

 natural unit of electricity is such that the quantity we reckon as one 

 coulomb, viz., that which one ampere conveys in one second 

 through any section of a conductor, is equal to 6 J trillion electrons 

 (= 6*25 x 10 1S ). These negative electrons are constituents of all 

 chemical atoms. An electrically neutral atom which has lost one or 

 more electrons is called a positive ion, and neutral atoms which have 

 lost or gained electrons are said to be ionised. There are arguments 

 in favour of the view that the majority of the atoms in metals and 

 other good conductors of electricity are in a state of intermittent 

 ionisation, and that intermingled with the atoms or positive ions, say 

 in a wire of copper, tungsten or carbon, there are electrons which are 

 jumping from atom to atom with great velocity. If we apply to the 

 wire an electromotive force this causes a drift of these electrons at 

 the instant they are free, in the opposite direction to the force (on 

 usual conventions), which drift or unidirectional motion is super- 

 imposed on the irregular motion and constitutes an electric current. 

 The drift velocity may be very slow compared with the velocity of 

 the irregular motion. The drift motion of the electrons superim- 

 posed on the irregular motion may be compared with that of a swarm 

 of bees in which each insect is flying hither and thither rapidly, 

 whilst the whole swarm is being blown by a gentle breeze slowly 

 down a road. 



If the electrons merely surge to and fro, it gives rise to a form of 



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