PETER GUTHRIE TAIT. 169 



effect, between two points whose difference in temperature is 1°C, when 

 a unit quantity of electricity passes between them. And Tait's work 

 amounted to showing experimentally that the 'specific heat of elec- 

 tricity/ as defined by Kelvin, was for any given substance directly pro- 

 portional to the absolute temperature. This is sometimes spoken of as 

 Tait's Law. 



From these experimental results Tait suggested the well-known 

 form of the thermo-electric diagrams, the rough preliminary sugges- 

 tions for which Lord Kelvin had already given. Under Taitfs 

 development the diagrams exhibit not merely the relative thermo- 

 electric positions of the metals at various temperatures, with their 

 neutral points, but also the specific heat of electricity in each metal in 

 terms of temperature, the amount of the Peltier effect, and the e. m. f. 

 (and its direction) for a circuit of any two metals with given tempera- 

 tures of the junctions.* 



2. Tait also discovered a multiplicity of neutral points for thermo- 

 electric couples of certain substances, such as circuits of iron coupled 

 with various alloys of platinum with iridium, nickel and copper. In 

 each of these cases there are at least two neutral points below the 

 temperature of white heat, and others at still higher temperatures. 



Professor Chrystal givesf the following vivid picture of Tait: 



Ready to take a blow, he did not always spare his strength in giving one, 

 and his opponents did not always relish his rough play. It may be doubted 

 whether many of them carried for long any resulting bitterness; but undoubtedly 

 some of them were led, temporarily at least, greatly to mistake his character. 

 Personal contact with him at once dissipated any such misconception. To feel 

 the magic of his personality to the full it was necessary to visit him in the 

 little room at the back of his house, the Spartan simplicity of whose plain deal 

 furniture and book-shelves, unpainted, unvarnished, ink-spotted, littered with 

 books and pamphlets and with piles of manuscript bristling with quaternion 

 symbols, was finely in tune with the tall, rugged figure, the loud, hearty greet- 

 ing and the radiant, welcoming smile of the kindly host. Ten minutes in that 

 sanctum would have made a friend of the bitterest foe. Thither at various 

 times came Joule, Andrews, Kelvin, Stokes, Helmholtz, Rankine, Clerk Maxwell, 

 Balfour Stewart, Rowland, the Wiedemanns (father and son), Adams, Newcomb, 

 Huggins, Newton, Lockyer, Hamilton (at least in spirit), Cayley, Sylvester, 

 Hermite, Cremona, Clifford, Klein, Bierens de Haan and many more, the 

 majority, alas, now departed like their common friend." 



* For a discussion of these diagrams see J. J. Thomson's Elec. and Mag., 

 pp. 499-505. 



t Nature, July 25, 1901. 



