Lord Kelvin: An account of his scientific life and work

by Andrew Gray

The imperfect sketch of Lord Kelvin's scientific life and work which this book contains can only give a faint notion of the great achievements of the long life that has now ended. Beyond the researches which he carried out and the discoveries he made, there is the inspiration which his work and example gave to others. Inspired himself by Lagrange, Laplace, Ampère, and Fourier, and led to experimental research by the necessity for answers to the questions which his mathematical expression of the discoveries of the twenty-five years which preceded the establishment of his laboratory had suggested—the theories of electricity and magnetism, of heat, of elasticity, his discoveries in general dynamics and in fluid motion, the publication of "Thomson and Tait," all made him the inspirer of others; and there was no one, however eminent, who was not proud to acknowledge his obligations to his genius. Clerk Maxwell, before he wrote the most original treatise on electricity that has ever appeared, gave himself to the study of Faraday's Experimental Researches and to the papers of Thomson. And if some, like FitzGerald and others, have regretted that the electromagnetic theory of light to which Maxwell was led by Faraday, and, indeed, by Thomson himself, did not meet with a more sympathetic reception at his hands, they have not been unmindful of the source from which much of their illumination has come.

He has founded a school of thought in mathematical physics, of men in whose minds the symbol is always the servant of the ideas, whose motto is interpretation by dynamical processes and models as far as that is possible, who shirk no mathematical difficulties when they have to be encountered, but are never led away from the straight road to the goal which they seek to reach—the systematic and clear formulation of the course of physical action.

And in Lord Kelvin's mind there was blended with a clear physical instinct which put aside all that was extraneous and unessential to the main issue an extraordinary power of concentration on the problem in hand, and a determination that was never daunted by failure, which consented to postponement but never to relinquishment, and which led often after long intervals of time to success in the end. He believed that light would come at last on the most baffling of problems, if only it were looked at from every point of view and its conditions were completely formulated; but he could put what was for the time impossible aside, and devote himself to the immediately possible and realisable. And as often happens with every thinker, his mind, released from the task, returned to it of itself, and what before appeared shrouded in impenetrable mist stood out suddenly sharp and distinct like a mountain-top before a climber who has at last risen above the clouds.

With the great mathematical power and sure instinct which led him to success in physical research was combined a keen perception of the importance of practical applications. Sometimes the practical question suggested the theoretical and experimental research, as when the needs of submarine telegraphy led to the discussion of the speed of signalling and the evolution of the reflecting galvanometer and the siphon recorder. On the other hand, the mathematical theory of electricity and magnetism had led to quantitative measurement and absolute units at an earlier time, when the need for these was beginning to be felt clearly by scientific workers and dimly by those far-sighted practical men who dreamed—for a dream it was thought at the time—of linking the Old World with the New by a submarine cable. But the quantitative study of electricity in the laboratory threw light on economic conditions, and the mass of data already obtained, mainly as a mere matter of experimental investigation of the properties of matter, became at once a valuable asset of the race of submarine cable engineers which suddenly sprang into existence.

And so it has been with the more recent applications of electricity. The induction of currents discovered by Faraday could not become of practical importance until its laws had been quantitatively discussed, a much longer process than that of discovery; and we have seen how the British Association Committee, led by Thomson and Maxwell, brought the ideas and quantities of this new branch of science into numerical relation with the units of already existing practical enterprise. The electrical measuring instruments—first the electrometers, and more recently the electric current balances and other beautiful instruments for the dynamo-room and the workshop—which Lord Kelvin invented have brought the precision of the laboratory into the everyday duties of the secondary battery attendant and the wireman.

And as to methods of measurement, those who remember the haziness of even telegraph engineers as to the measurement of the efficiency of electrical currents and electromotive forces in the circuits of lamps and dynamos, in the early days of electric lighting, know how much the world is indebted to Thomson.[26] He it was who showed at first how cables were to be tested, as well as how they were to be worked; it was his task, again, to show how instruments were to be calibrated for practical measurement of current and energy supplied by the early contractors to consumers. He had in the quiet of his laboratory long before elaborated methods of comparing resistances, and given the Wheatstone balance its secondary conductors for the comparison of low resistances; he now showed how the same principles could be applied to measure the efficiencies of dynamos and to make up the account of charge and discharge for a secondary battery.

And if the siphon-recorder and the mariners' compass and the sounding machine proved pecuniarily profitable, the reward was that of the inventor, who has an indefeasible right to the fruit of his brain and his hand. But Lord Kelvin's activity was not confined merely to those practical things which have, to use the ordinary phrase, "money in them"; he gave his time and energies freely to the perfecting of the harmonic analysis of the tides, undertook again, for a Committee of the British Association, the investigation of the tides for different parts of the world, superintended the analysis of tidal records, and invented tide-predicting machines and improved tide-gauges.

Lord Kelvin's work in the theory of heat and in the science of energy generally would have given him a title to immortality even if it had stood alone; and there can be no doubt, even in the mind of the most determined practical contemner of the Carnot cycle, of the enormous importance of these achievements. Here he was a pioneer, and yet his papers, theoretical and yet practical, written one after another in pencil and despatched, rough as they were, to be printed by the Royal Society of Edinburgh, form, as they are collected in volume i of his Mathematical and Physical Papers, in some respects the best treatise on thermodynamics at the present time! There are treatises written from a more general standpoint, which deal with complex problems of chemical and physical change of means of thermodynamic potentials, and processes which are not to be found set forth in this volume of papers; but even these are to a great extent an outcome of his "Thermoelastic, Thermomagnetic and Thermoelectric Properties of Matter."

In hydrodynamics also Lord Kelvin never lost sight of practical applications, even while pursuing the most intensely theoretical researches into the action of vortices or the propagation of waves. In his later years he worked out the theory of ship-waves with a power which has made more than one skilful and successful cultivator of this branch of science say that he was no mere mathematician, but a man who, like the prophets of old, could divine what is hid from the eyes of ordinary mortals. Of the ultimate importance of these for practical questions of the construction of ships, and the economy of fuel in their propulsion, there can be little doubt. Unhappily, the applications will have now to be made by others.

It is interesting to note that the investigation of waves in canals with which Lord Kelvin recently enriched the Proceedings of the Royal Society of Edinburgh have been carried out by a strikingly ingenious adaptation of the Fourier solution of the differential equation of the diffusion of heat along a bar, or of electricity along a slowly worked cable. Thus, beginning with Fourier mathematics in his earliest researches, he has in some of his last work applied the special exponential form of Fourier solution of the diffusion equation to a case, that of wave propagation, essentially different in physical nature, and distinct in mathematical signification, from that for which it was originally given.