462 



NATURE 



[January 8, 1920 



At present the whole question of the water 

 resources, and especially of the water-power, of 

 the British Isles is being: investigated by a Com- 

 mittee of the Board of Trade, and on this account 

 Parliament may be inclined to postpone the con- 

 sideration of private Bills dealing with water, if 

 not of special urgency, until the Committee has 

 reported. There are few areas in England where 

 an unused gathering-ground exists at an altitude 

 allowing of the development of water-power, and 

 it may well be considered inexpedient to allocate 

 them finally before a hydrometric survey has been 

 carried out to enable the available power and its 

 cost to be calculated on a sure basis before work 

 is commenced. 



RADIO-COMMUNICATION AND THE 

 THERMIONIC VALVE. 

 (i) The Thermionic Valve ar.d its Developments in 

 Radiotelegraphy and Telephony. By Prof. J. A. 

 Fleming. Pp. xv + 279. (London : The Wire- 

 less Press, Ltd., 191 9.) Price 155. net. 

 (2) Text-hook on Wireless Telegraphy. By Prof. 

 Rupert Stanley. New edition in two volumes. 

 Vol. i. : General Theory and Practice. Pp. xiii + 

 471. \'ol. ii. : Valves and Valve Apparatus. 

 Pp. ix + 357. (London: Longmans, Green, and 

 Co., 1919.) Price 155. net per vol. 

 (i)QCIENTIFIC workers who desire to learn 

 1^ something about the latest developments 

 in radio-communication generally find that books 

 on the subject are either scientific but too tech- 

 nical, or not sufficiently scientific and so useless for 

 their purpose. It is little use to have illustrations 

 of the kenotron, the pliodynatron, the ultra-audion, 

 and the tungar, with diagrams of their connec- 

 tions, unless we have also some reasoned account 

 of their mode of action. The reader soon tires also 

 of vague accounts of the electron theory, which is 

 regarded by some authors as a kind of fetish 

 which must never be criticised and the mere men- 

 tion of which is supposed to explain everything. 



In the first chapter Prof. Fleming gives an inter- 

 esting and instructive historical introduction. So 

 far back as. 1883 he read a paper to the Physical 

 Society describing the molecular radiation in incan- 

 descent lamps with horse-shoe filaments. He 

 proved that the blackening of the bulb was due 

 to the scattering in straight lines of carbon par- 

 ticles from the filaments, one leg of the horse-shoe 

 filament protecting a long strip of the bulb from 

 being blackened. 



Later in the same year Edison discovered that a 



current would flow between the positive terminal of 



the filament and a metal plate sealed in the bulb. 



In those pre-electron days the phenomenon was 



NO. 2619. VOL. 104] 



considered by electricians hopelessly puzzling. In 

 1897 Sir J. J. Thomson first published an account 

 of his demonstration that negative electricity is 

 always associated with certain masses about 1800 

 times smaller than the mass of an atom of hydro- 

 gen, and that under certain conditions these elec- 

 tric corpuscles are emitted from hot bodies. It 

 then became possible to give a scientific explana- 

 tion of the Edison effect. It was not, however, 

 until 1904 that Prof. Fleming published his master 

 patent, which proved the utility of the Edison 

 effect in radio-telegraphy. 



The Fleming valve, which is the parent of all 

 the thermionic valves, allows electricity to flo\\ 

 from a heated filament to a cylinder, both being 

 enclosed in a vacuum bulb, provided the cylinder 

 be at a higher potential than the filament. If the 

 potential be lower than that of the filament, tlien 

 practically no current flows. The device thus Ects 

 as a true valve, allowing current to flow in one 

 direction, but not in the other. The high-frequency 

 currents in the aerial can thus be rectified, and the 

 consequent gushes of electricity in one direction 

 can magnetise the electromagnet of the telephone 

 and thus produce a sound. 



In chap. iii. a description is given of several 

 types of three-electrode valve and of the various 

 ways they can be connected up. Special stress is 

 laid on the historical side of the development of 

 this valve. In chap. iv. we are told of the (lis- i 

 covery that the three-electrode thermionic valve 

 could in certain circumstances act as a generator 

 of oscillations. It would be of interest to know 

 who suggested to Meissner that he should try 

 whether it was possible to make the thermionic 

 relay into a generator. Whoever it was deserves 

 great credit for his suggestion. 



Prof. Fleming points out how analogous the 

 action of the generator valve is to that of the 

 "humming telephone," which has been known 

 to electricians for the last twenty-five years, and 

 also, but not so obviously, to that of the Duddell 

 arc. 



The great advantage of the thermionic valve as 

 a detector in practical work is that it is not liable 

 to be damaged by electric atmospheric discharges, 

 which often cause endless trouble when coherers 

 or crystal detectors are employed. In chap. v. the 

 uses of the thermionic detector in radio-telephony 

 are described, the complicated diagrams being 

 quite easy to follow, partly because of the use of 

 the excellent system of symbols standardised by 

 radio-engineers. In chap. vi. descriptions are 

 given of the methods of using thermionic devices 

 in radio-telephony. We are pleased to rote that 

 due credit is given to •H. J. Round, of the Mar- 

 coni Co., for his numerous inventions. 



