1990-04: Sir Ambrose Fleming

When 1 Think Back.. by Neville Williams Sir John Ambrose Fleming: He invented radio valves - or did he? Dr/Professor Sir John Ambrose Fleming is remembered primarily as the inventor of the Fleming thermionic, diode and the 'father' of radio valves, which were fundamental to the subsequent development of the industry. Whether or not this is strictly correct is debateable but, either way, Ambrose Fleming made a very considerable contribution to basic electrical and electronic technology. Curiously, one finds scant mention, in patent rights in respect to the ther- relevant textbooks, of Fleming's per- mionic diode; but more about that later! sonal background or his academic ca- Sir John Ambrose Fleming - a gifted reer. Beyond the fact that he was born Fleming the academic scientist of his day. in 1849, the texts to which I had access Curious about Fleming's academic ca- make little or no reference to his birth- reer, I checked through a number of old I have little doubt that the 'rules-of- place, his family or the steps in his ca- reference books in my possession. thumb' we were invited to memorise in reer which led to his ultimate knight- First off, a brief entry in a 60-year old other days were devised by John Am- hood. Pear's encyclopedia indicated that Flem- brose Fleming, the subject of this pre- The British technical writer/consultant ing's involvement with the University sent article. S. Handel comes closest in The Elec- College spanned 40-odd years, from There is no ambiguity, however, tronic Revolution (Penguin Books, UK, 1885 to 1926, by which time he would about the Dr J.A. Fleming whose work 1967). I quote: have been in his mid '70s. features prominently in another old Next in line was a 1931 copy of the textbook: The Calculation and Measure- At the turn of the century Fleming, Admiralty Handbook. Prompted by the ment of Inductance and Capacity, by then a young professor of electrical engi- index, I re-discovered several long-for- W.H. Nottage of the Marconi Works, neering at University College in London, gotten references to Fleming's left-hand Chelmsford (Wireless Press, London, was appointed scientific adviser to the and right-hand rules, which correlate 1916). Edison Electric Light Company of Lon- current flow, the direction of magnetic Nottage quotes basic research into ca- don and became familiar with Edison's flux and the mechanical force in mag- pacitance by Fleming, as described in lamp experiments. He subsequently be- netic systems (Fig.1). his book The Principles of Electric came a consultant to the British Marconi The 'Fleming' responsible is not iden- Wave Telegraphy, 2nd Edition, page Company which was looking for a better tified by the Admiralty Handbook, but 179. detector of wireless signals than the clumsy and troublesome devices used by Marconi. It so happens that Handel was, him- self, educated at the same University. Clearly, in the 50-odd years between 1849 and the turn of the century, Flem- ing had earned sufficient recognition at an academic and practical level to com- Fig.1: Fleming's mend him as an independent consultant left-hand rule for remembering the to the Edison & Swan Electric Light relationship group and later (in 1889) to the newly between motion, formed British Marconi company. magnetic field As a consultant, he had ready access and induced to Edison's lamp technology and to voltage. Marconi's pioneering ventures into wireless telegraphy — involvements that complicated subsequent litigation about 20 ELECTRONICS Australia, April 1990 A further reference is to adjustable mionic diode appears to be in relatively waveform filters devised by Fleming and low key. A snippet of a letter to Marco- Dyke, to facilitate their investigations ni, in his own handwriting, reproduced into power factor and the conductivity with the above-mentioned Practical of dielectrics. (j.I.E.E. , xlix 1912, Wireless article gives no hint that Flem- p.323). ing's evaluation of the diode extended Again, a method of measuring capaci- beyond his immediate area of concern tance is described, with a low-resistance — a potentially useful method of sensing battery as a DC source. Attributed to wireless telegraphy signals. It reads: Fleming & Clinton, it used a spinning I have found a method of rectifying commutator to pulse charge the un- electrical oscillations that is making the known, capacitance at a rate of typically Fig.4: The Fleming-Anderson bridge, flow of electricity all in the same direc- 100pps and to pulse discharge it alter- developed to measure inductance. tion, so that I can detect them with an nately at the same rate through a ballis- ordinary mirror galvanometer. tic galvanometer, the readout being in- I have been receiving signals on an terpreted in terms of capacitance. The Fleming-Anderson bridge (Fig.4) aerial with nothing but a galvanometer (Fig.2). provided a means of measuring induct- and my device, but at present only on a ance. According to the text, it could be laboratory scale. used with alternating current input or This opens up a wide field of work, as with direct current in conjunction with a I can now measure exactly the effect of buzzer-interrupter or a make-and-break the transmitter. key. It was nulled by adjusting for I have not mentioned this to anyone minumum sound in the phone T, but yet as it may become very useful. could reportedly yield more accurate re- Yours very sincerely, sults with the benefit of measurement J.A. Fleming. methodology described in Watson's Fig.2: Fleming and Clinton devised Practical Physics. Contemporary paper this simple system for measuring If the above is more characteristic of capacitance, using a galvanometer. Fleming & the diode an academic than an enthusiast and a According to Nottage, the method While there is ample evidence as visionary, the same goes for his contem- was detailed in Dr Fleming's books: above of an active and innovative aca- porary paper on the thermionic diode, a Wireless Telegraphist's Pocket Book demic career, the fact remains that most copy of which was made available to me and The Principles of Electric Wave biographical references to Fleming con- some time ago by Mr C.H. Scott of Ip- Telegraphy and Telephony, published at centrate on his rationalisation of the so- the time by Wireless Press, UK. called 'Edison effect' culminating, in (A similar contemporary title by November, 1904, in the almost legend- Fleming, An Elementary Manual of Ra- ary Fleming diode. diotelegraphy and Radiotelephony was For sure, it was an important break- quoted as a reference by Peter Jensen through in its in own right, but to ac- for his article 'Spark: an old-time Induc- claim Fleming's elementary thermionic tion Coil' in the April and June '89 diode as the the original radio valve and issues of this magazine). the genesis of the electronic revolution But back to Nottage: the measure- may be open to question. ment bridge illustrated in Fig.3 is cred- That he was so acclaimed is evidenced ited to Fleming and Dyke and was used by the fact that, in 1927, a landmark by them to measure capacitance or, year for wireless broadcasting, full-page more importantly, in researching power advertisements in popular wireless factor and the conductivity of dielec- magazines for Amplion horn loudspeak- trics. ers carried a personalised product en- dorsement by Dr J.A. Fleming, described as 'the original inventor of the thermionic valve' (see illustration). More recently, on the 60th anniversary of the Fleming diode, the well known English journal Practical Wire- less for January 1965 published a com- memorative article under the heading: 'FLEMING ... AND THE DIODE — 60th Anniversary of the invention of the Thennionic Valve by Sir Ambrose Fleming FRS.' Quite a few writers insist, however, Fig.3: The capacitance measurement that some of the credit allocated to Fleming's first experimental diode bridge attributed to Fleming and Fleming really belongs to others. Again detector valve, developed in 1904. it Dyke, by Nottage. It also measured — more about this later! became the subject of considerable dielectric performance. Fleming's own reaction to the ther- legal argument. ELECTRONICS Australia, April 1990 21 When I Think Back swich, Qld. It comes from Technics, a monthly publication from George Newnes, London, dated April 1905. Contemplating such an innovation, one rather expects a title along the lines of: 'A New and Revolutionary Method of Detecting Wireless Signals'. Instead, we have the bland and predominately academic heading: 'On the Electric Conductivity of a Vacuum' by J.A. Fleming, MA, DSc, FRS. Perhaps wireless communication and a device based on electron emission was The Marconi wireless station at Poldhu, in Cornwall, UK, pictured in 1901. such a non-issue to readers of Technics Designed by Fleming, it was used for the first trans-Atlantic communication. in 1905 that the notion of an electrically conductive vacuum was judged to be minium plate, in some electrolyte yield- the applied voltages, along with phos- more titillating; that's certainly the way ing oxygen, then a current of positive phorescence and other phenomena to it's presented by the author. electricity can pass from the carbon to do with Crookes and Roentgen tubes. In the paper, Fleming envisages a the aluminium but not in the reverse di- He also makes the point that current glass tube containing two electrically ac- rection. due to the presence of free electrons To explain conduction by an evacu- cessible platinum plates, the whole as- can be drawn off by inserting a carbon sembly being sealed and evacuated to ated thermionic diode, along with a rec- or water-cooled iron probe into the ac- tifying action, Fleming says: one hundred-millionth of an atmos- tive, ionised region of an arc.

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