Valve Developments

Radio Record, Volume II, Issue 47, 7 June 1929, Page 30

Valve Developments

Review by Dr. as

Fleming

R. J. A. FLEMING, the famous scientist and inventor of the thermionie valve, has recently given a review of the subsequent development of his invention, together with some observations as to the possible future lines of discovery. Coming from one so intimately associated with the subject as Dr. Fleming, these remarks are of peculiar interest. You will remember that he discussed the question as to the source of the electrons which are emitted from the filament of a radio valve. It would appear that in the case of a pure metal filament-tungsten, for example-heat-ed by an electric current in a high vacuum, the electrons which escape from the filament as thermions are simply the free-moving electrons . which are considered to move in the inter-atomic spaces, and which are responsible for metallic conduction. this theory be correct, then obviously the electrons come originally from the batteries. You will find it very interesting to consider whether

they "come from the low-tension filament heating battery, or from the hightension battery. As ‘you know, you can get a considérable amount of electron emission by the use simply of a lowtension heating battery’ without any high-tension -battery at all, and therefore in his case it is cledr (assuming the electrons are not' due to changes in the atoms of the filament themselves) that they come from the filament heating battery. On the other hand, where a high-ten-sion battery is used, it is clear that this passes a current between the filament and anode, which current consists ‘of an electronic stream, and, therefore, it is reasonable to suppose that the current comes from the high-tension battery.