December 26, 1907] 



NA TURE 



177 



units of length, mass and time. Moreover, toward the 

 end of the 'fifties, electric measurement, in the hands of 

 the cable engineers, had become much developed, and 

 instruments of a precision exceeding anything known 

 then in the physical laboratory had been devised for 

 practical use. In i86i Lord Kelvin secured the 

 appointment by the British Association of a committee 

 on electrical standards, a committee of which also 

 Wheatstone, Matthiessen, Fleeming Jenkin, and, 

 later, Siemens, Clerk Maxwell, Joule, and Carey 

 Foster were members. Year after year this com- 

 mittee, with younger men added, has produced its 

 reports with little intermission, and the system of 

 units which it evolved is practically that which is 

 internationally recognised and of legal force. Twice 

 Lord Kelvin gave public expositions of the system in 

 set addresses, at a South Kensington conference in 

 1876, and before the Civil Engineers in 1SS3. The 

 latter of these discourses is in Lord Kelvin's most 

 characteristic style, and even now, after twenty years, 

 some of it is hard reading for any but a professed 

 physicist. But mere hardness never daunted Lord 

 Kelvin. In the same lecture, speaking of a particular 

 point in tlie system of absolute measurement, he said : — 

 " It mav be hard to accept, but the harder it is the 

 more it is worth thinking of." The acceptance and 

 rapid development of the international system, based 

 on the centimetre, the gram, and the second, is due 

 to Lord Kelvin more than to any other man. 



After the adoption of the new units by the Inter- 

 national Congress at Paris in 188 1, Lord Kelvin de- 

 voted much attention to the production of commercial 

 instruments for the measurement of current, potential, 

 and electric power. Relying confidently on the right- 

 ness of abstract principles, he produced a series of am- 

 pere-balances for currents of different strengths, thus 

 putting into the hands of practical engineers a set of 

 instruments of remarkably great accuracy and of re- 

 markable range. When occupied with the tides, in 

 tlie 'seventies, he had devised a machine for analysing 

 the harmonic components of the periodic tidal vari- 

 ations, the essential part of this harmonic analyser 

 being a mechanical integrating device of globe, disc, 

 and cylinder, first suggested by his brother," Prof. 

 James Thomson. It seemed a bold thing to apply 

 such mechanism to evaluate the integrals indicated 

 by Fourier's analysis; but Kelvin's machine justified 

 the hardihood of the conception. When in the 

 'eighties he had before him the problem of construct- 

 ing an electricity meter which should continuously 

 integrate the varying product of current and voltage 

 of an electric supply, he again had recourse to the 

 same integrating mechanism. And, here, it may be 

 remarked in passing that it is to Lord Kelvin's 

 evidence before the Parliamentary Committee in 1879 

 that we owe the circumstance that the Board of 

 Trade adopted as its official unit of electric energy 

 the value of one thousand volt-ampere-hours. It was 

 once upon a time proposed to denominate this unit — 

 now universally employed — by the name of one " kel- 

 vin." Lord Kelvin's innate modesty caused him to 

 reject the suggestion. Surely the time has now come 

 for the final incorporation of his name into the inter- 

 national system, thus linking it with those of Volta, 

 .Ampere, Ohm, Coulomb, Watt, Faraday, Joule, 

 Henry, and Gauss. 



Lord Kelvin had a peculiar predilection for illus- 

 trating recondite notions bv models. He once said 

 that he could never understand a thing until he could 

 make (or conceive) a model of it. His chain of gyro- 

 stats to illustrate the rigidity of the ether, his systems 

 of crystal models made of little wooden rods and balls 

 held in stable equilibrium by india-rubber bands, are 

 but two examples of a mode of using the concrete to 

 realise the abstract that he practised continually. He 



NO. iqqi, VOL. 77] 



was fond of introducing into abstract dynamics terms 

 derived from other sciences, geodesy, and crystallo- 

 graphy. .'Amongst the bye-products of his genius may 

 be found enshrined in the Proceedings of the Royal 

 Society a short paper containing the essentials of the 

 theory of the designing of wall-paper patterns; its 

 title, however, is " The Homologous Partition of 

 Space." 



Of Lord Kelvin's later work on molecular physics, 

 the " tactics of a crystal," the problems of aeolotropic 

 elasticity in relation to optical as well as magnetic and 

 electric phenomena, it is less easy to speak. The lec- 

 tures which he gave at Baltimore in 1S84 to " his 

 twenty-one coefficients," the members of the group of 

 accomplished physicists who then sat at his feet day 

 after day, while he led them through the mazes of the 

 elastic-solid theory and the newly-invented spring- 

 shell molecule, remain a witness to his extraordinary 

 fertilitv of intellectual resource. .All his life he had 

 been endeavouring to discover a rational mechanical 

 explanation for the most recondite phenomena — the 

 mvsteries of magnetism, the marvels of electricity, the 

 difficulties of crystallography, the contradictory pro- 

 perties of ether, the anomalies of optics. And during 

 the preceding decade he had been confronted with a 

 great generalisation which did not fit in with this 

 method of Intellectual apprehension, which had become 

 to him instinctive. While Kelvin had been seeking to 

 explain electricity and magnetism and light mechanic- 

 ally, or as mechanical properties, if not of matter, at 

 least of ether, Maxwell had boldly propounded the 

 electromagnetic theory of light, and had drawn all the 

 younger men after him in acceptance of the general- 

 isation that the waves. Lord Kelvin had never ac- 

 cepted Maxwell's theory. It is true that in 1888 he 

 gave a nominal adhesion ; but later withdrew it, pre- 

 ferring still to think of things in his own way. Kelvin's 

 Baltimore lectures of 1884, abounding as they do in 

 a host of brilliant and ingenious points, and ranging 

 from the most recondite problems of optics to specu- 

 lations on crystal rigidity and molecular dynamics, 

 leave one with a sense of being a sort of protest of a 

 man persuaded against his own instincts, and strug- 

 gling to find new expression of his thoughts so as to 

 retain his old ways of regarding the ultimate dynamics 

 of physical nature. During the last few years of his 

 life Lord Kelvin himself revised these lectures, enrich- 

 ing them with a variety of new materials, and coordin- 

 ating the old. He was intensely interested in the new 

 problems raised by the discovery of radium ; and in its 

 astonishing property of continuously emitting bent. 

 He combated strenuously the hypothesis of Ruther- 

 ford that this was to be explained by a spontaneous 

 decomposition of the atom ; and to the very last he was 

 seeking for other explanations. 



.\t the present time, when so much of the new 

 knowledge is in a state of flux, it would be entirely 

 premature to attempt to evaluate the ultimate import- 

 ance of Lord Kelvin's later writings on radium and 

 on the " electrions." Suffice it to say that he brought 

 to bear on these things the same illuminating genius, 

 the same keen analytical instincts, that he had shown 

 throughout his long career. 



To two generations, if not three, of scientific men 

 his work, his presence, his mathematical genius, his 

 enthusiastic faith in first principles, and his unfailing 

 gentle courtesy have been an inspiration and a per- 

 petual stimulus. So he rests from his labours, and his 

 works do follow him. Silvanus P. Thompson. 



Lord Kelvin's Funeral in Westminster Abbey. 

 The decision taken by the Dean of Westminster to 

 accord to Lord Kelvin burial in Westminster Abbey 

 met at once with a warm and responsive echo of satis- 

 faction on the part of men of science and the com- 



