THERMOELECTRICITY 345 



luminous and visible. The stream passed between two plates which could 

 be brought at will to different electrical potentials. When the electric field 

 was established with the lines of force passing upwards, each negatively 

 charged particle was subject to a vertical force analogous to the force of 

 gravity in the case of the golf ball. The luminous stream showed the 

 path described by each particle. This corresponded to the golf ball path 

 when there was no underspin, as in fig. 4 on p. 341. A force analogous 

 to the upward force which acts on the properly spinning golf ball was then 

 applied to the moving electrified particles by introducing" a magnetic field, 

 with lines of magnetic force passing horizontally across the stream. The 

 moving particles were driven at right angles to their own motion and to 

 the line of magnetic force. By suitable adjustment of direction and strength 

 of magnetic field, the luminous stream could be made to assume forms 

 identical with those figured by Tait in the curves on page 341. By increasing 

 the strength of the field Sir J. J. Thomson obtained not only the kink figured 

 on page 342, which Tait had demonstrated with the light rubber balloon, 

 but he also obtained a succession of loops or kinks in the luminous stream. 



The following paragraphs contain additional notes on three aspects of Tait's 

 life and work. The first note discusses some recent developments of thermoelectric 

 theory, the second touches on the social side of Tait's character, and the third 

 supplies further information regarding the production of one of Tait's most characteristic 

 books. 



THERMOELECTRICITY. 



Mr J. D. Hamilton Dickson, M.A., of Peterhouse, Cambridge, has 

 recently discussed with remarkable skill and ingenuity the data supplied 

 by Sir James Dewar and Professor Fleming's measurements 1 of the thermo- 

 electric properties of various metals from 20x3 C. to + 100 C. His con- 

 clusions, which are of great interest and form an important extension of 

 Tait's early results, were read before the Royal Society of Edinburgh on 

 Nov. 7, 1910, and are being published in full in the Transactions of that 

 Society. 



As noted on page 79 above, one of Tait's main results was that through 

 a considerable range of temperature the electromotive force between a given 

 pair of metals was in general a parabolic function of the difference of 



1 Phil. Mag., July 1895, Vol. XL, pp. 95-119. 

 T. 44 



