Laws regarding Direction of Thermo-electric Currents. 509 



Berget, o£ 2 others according to Wiedemann and Franz, and 

 on the electrical conductivities o£ 12 o£ them according to 

 Latimer Clark, and of 1 other according to Becqnerel. Of 

 the heat conductivities of the 9 metals thus obtained 

 M. Thomas states himself that he modifies 4 by amounts 

 varying from 2 to 10 per cent, in order to make the values 

 of the products fit in with his laws *. As he had no values 

 for the heat conductivities of the remaining 6 metals, 

 nor for the electrical conductivities of 3 of the metals, he 

 states himself that he assumes values for these quantities 

 which fit in with his lawf. 



It cannot be claimed that such a method of treatment pro- 

 vides a firm support for the theory advanced by M. Thomas, 

 and it is necessary to examine it more critically in the light of 

 the more accurate values of the constants which are available. 



In the first place, it is possible to put the theory into a 

 more compact form than that adopted by M. Thomas. 

 According to him, if electrical conductivity of the better 

 •electrical conductor x heat conductivity of the worse electrical 

 conductor is greater than electrical conductivity of the worse 

 electrical conductor x heat conductivity of better electrical 

 conductor the thermo -current flows from hot to cold in the 

 better electrical conductor. 



If, on the other hand, electrical conductivity of better 

 electrical conductor x heat conductivity of worse electrical 

 conductor is less than electrical conductivity of worse elec- 

 trical conductor x heat conductivity of better electrical con- 

 ductor the thermo-current flows from hot to cold in the worse 

 electrical conductor. 



Dividing the inequalities through by the product of the heat 

 conductivities of the two metals, the statements become : — 



T „ electrical conductivity • .' .. , . . , 



It — r — i 5 — rr-r. — - or better electrical conductor 



heat conductivity 



> electrical conductivity , i i • i i .i 



_- — i ; : — rr—r, — - or worse electrical conductor the 



^- neat conductivity 



* With regard to the values for these four metals— copper, gold, iron, 

 And lead — M.Thomas says (p. 904): — "Si je les acceptais tels qu'ils 

 sont, j'aurais necessairement un petit nombre de couples dont le sens du 

 courant ne repondrait pas a mes lois. Je les ai done modifies legerernent 

 ainsi qu'il suit : — " 



f Of the latter quantities M. Thomas says (p. 906) : — " Je ne connais 

 ni les coefficients de conductibilite" electrique, ni les coefficients de con- 

 •ductibilite" calorifique du cobalt,, du manganese et de l'arsenic, .... Je 

 prendrai done par hypothese pour coefficients du conductibilite electrique 

 du cobalt, du manganese, et de l'arsenic les nombres 1380, 1000, et 200." 



