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Memoir of Fleeming Jenkin, a non-fiction book by Robert Louis Stevenson |
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_ NOTE ON THE CONTRIBUTIONS OF FLEEMING JENKIN TO ELECTRICAL AND ENGINEERING SCIENCE. BY SIR WILLIAM THOMSON, F.R.S., LL D., ETC., ETC. IN the beginning of the year 1859 my former colleague (the first British University Professor of Engineering), Lewis Gordon, at that time deeply engaged in the then new work of cable making and cable laying, came to Glasgow to see apparatus for testing submarine cables and signalling through them, which I had been preparing for practical use on the first Atlantic cable, and which had actually done service upon it, during the six weeks of its successful working between Valencia and Newfoundland. As soon as he had seen something of what I had in hand, he said to me, 'I would like to show this to a young man of remarkable ability, at present engaged in our works at Birkenhead.' Fleeming Jenkin was accordingly telegraphed for, and appeared next morning in Glasgow. He remained for a week, spending the whole day in my class-room and laboratory, and thus pleasantly began our lifelong acquaintance. I was much struck, not only with his brightness and ability, but with his resolution to understand everything spoken of, to see if possible thoroughly through every difficult question, and (no if about this!) to slur over nothing. I soon found that thoroughness of honesty was as strongly engrained in the scientific as in the moral side of his character. In the first week of our acquaintance, the electric telegraph and, particularly, submarine cables, and the methods, machines, and instruments for laying, testing, and using them, formed naturally the chief subject of our conversations and discussions; as it was in fact the practical object of Jenkin's visit to me in Glasgow; but not much of the week had passed before I found him remarkably interested in science generally, and full of intelligent eagerness on many particular questions of dynamics and physics. When he returned from Glasgow to Birkenhead a correspondence commenced between us, which was continued without intermission up to the last days of his life. It commenced with a well-sustained fire of letters on each side about the physical qualities of submarine cables, and the practical results attainable in the way of rapid signalling through them. Jenkin used excellently the valuable opportunities for experiment allowed him by Newall, and his partner Lewis Gordon, at their Birkenhead factory. Thus he began definite scientific investigation of the copper resistance of the conductor, and the insulating resistance and specific inductive capacity of its gutta-percha coating, in the factory, in various stages of manufacture; and he was the very first to introduce systematically into practice the grand system of absolute measurement founded in Germany by Gauss and Weber. The immense value of this step, if only in respect to the electric telegraph, is amply appreciated by all who remember or who have read something of the history of submarine telegraphy; but it can scarcely be known generally how much it is due to Jenkin. Looking to the article 'Telegraph (Electric)' in the last volume of the old edition of the 'Encyclopaedia Britannica,' which was published about the year 1861, we find on record that Jenkin's measurements in absolute units of the specific resistance of pure gutta-percha, and of the gutta-percha with Chatterton's compound constituting the insulation of the Red Sea cable of 1859, are given as the only results in the way of absolute measurements of the electric resistance of an insulating material which had then been made. These remarks are prefaced in the 'Encyclopaedia' article by the following statement: 'No telegraphic testing ought in future to be accepted in any department of telegraphic business which has not this definite character; although it is only within the last year that convenient instruments for working, in absolute measure, have been introduced at all, and the whole system of absolute measure is still almost unknown to practical electricians.' A particular result of great importance in respect to testing is referred to as follows in the 'Encyclopaedia' article: 'The importance of having results thus stated in absolute measure is illustrated by the circumstance, that the writer has been able at once to compare them, in the manner stated in a preceding paragraph, with his own previous deductions from the testings of the Atlantic cable during its manufacture in 1857, and with Weber's measurements of the specific resistance of copper.' It has now become universally adapted - first of all in England; twenty-two years later by Germany, the country of its birth; and by France and Italy, and all the other countries of Europe and America - practically the whole scientific world - at the Electrical Congress in Paris in the years 1882 and 1884. An important paper of thirty quarto pages published in the 'Transactions of the Royal Society' for June 19, 1862, under the title 'Experimental Researches on the Transmission of Electric Signals through submarine cables, Part I. Laws of Transmission through various lengths of one cable, by Fleeming Jenkin, Esq., communicated by C. Wheatstone, Esq., F.R.S.,' contains an account of a large part of Jenkin's experimental work in the Birkenhead factory during the years 1859 and 1860. This paper is called Part I. Part II. alas never appeared, but something that it would have included we can see from the following ominous statement which I find near the end of Part I.: 'From this value, the electrostatical capacity per unit of length and the specific inductive capacity of the dielectric, could be determined. These points will, however, be more fully treated of in the second part of this paper.' Jenkin had in fact made a determination at Birkenhead of the specific inductive capacity of gutta-percha, or of the gutta-percha and Chatterton's compound constituting the insulation of the cable, on which he experimented. This was the very first true measurement of the specific inductive capacity of a dielectric which had been made after the discovery by Faraday of the existence of the property, and his primitive measurement of it for the three substances, glass, shellac, and sulphur; and at the time when Jenkin made his measurements the existence of specific inductive capacity was either unknown, or ignored, or denied, by almost all the scientific authorities of the day. The original determination of the microfarad, brought out under the auspices of the British Association Committee on Electrical Standards, is due to experimental work by Jenkin, described in a paper, 'Experiments on Capacity,' constituting No. IV. of the appendix to the Report presented by the Committee to the Dundee Meeting of 1867. No other determination, so far as I know, of this important element of electric measurement has hitherto been made; and it is no small thing to be proud of in respect to Jenkin's fame as a scientific and practical electrician that the microfarad which we now all use is his. The British Association unit of electrical resistance, on which was founded the first practical approximation to absolute measurement on the system of Gauss and Weber, was largely due to Jenkin's zeal as one of the originators, and persevering energy as a working member, of the first Electrical Standards Committee. The experimental work of first making practical standards, founded on the absolute system, which led to the unit now known as the British Association ohm, was chiefly performed by Clerk Maxwell and Jenkin. The realisation of the great practical benefit which has resulted from the experimental and scientific work of the Committee is certainly in a large measure due to Jenkin's zeal and perseverance as secretary, and as editor of the volume of Collected Reports of the work of the Committee, which extended over eight years, from 1861 till 1869. The volume of Reports included Jenkin's Cantor Lectures of January, 1866, 'On Submarine Telegraphy,' through which the practical applications of the scientific principles for which he had worked so devotedly for eight years became part of general knowledge in the engineering profession. Jenkin's scientific activity continued without abatement to the end. For the last two years of his life he was much occupied with a new mode of electric locomotion, a very remarkable invention of his own, to which he gave the name of 'Telpherage.' He persevered with endless ingenuity in carrying out the numerous and difficult mechanical arrangements essential to the project, up to the very last days of his work in life. He had completed almost every detail of the realisation of the system which was recently opened for practical working at Glynde, in Sussex, four months after his death. His book on 'Magnetism and Electricity,' published as one of Longman's elementary series in 1873, marked a new departure in the exposition of electricity, as the first text-book containing a systematic application of the quantitative methods inaugurated by the British Association Committee on Electrical Standards. In 1883 the seventh edition was published, after there had already appeared two foreign editions, one in Italian and the other in German. His papers on purely engineering subjects, though not numerous, are interesting and valuable. Amongst these may be mentioned the article 'Bridges,' written by him for the ninth edition of the 'Encyclopaedia Britannica,' and afterwards republished as a separate treatise in 1876; and a paper 'On the Practical Application of Reciprocal Figures to the Calculation of Strains in Framework,' read before the Royal Society of Edinburgh, and published in the 'Transactions' of that Society in 1869. But perhaps the most important of all is his paper 'On the Application of Graphic Methods to the Determination of the Efficiency of Machinery,' read before the Royal Society of Edinburgh, and published in the 'Transactions,' vol. xxviii. (1876-78), for which he was awarded the Keith Gold Medal. This paper was a continuation of the subject treated in 'Reulaux's Mechanism,' and, recognising the value of that work, supplied the elements required to constitute from Reulaux's kinematic system a full machine receiving energy and doing work.
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