Page:Popular Science Monthly Volume 61.djvu/175

Rh 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 electricity' as defined by Kelvin, was for any given substance directly proportional 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 suggestions for which Lord Kelvin had already given. Under Tait's 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 temperatures 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 gives 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 greeting 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."