62 Prof. L. Lorenz on the Determination of 



artificially produced difference of temperatures, if we apply the 

 laws discovered by Dufour, is diminished by the process of dif- 

 fusion itself. Accordingly we find between thermodiffusion and 

 Dufour's discovery a reciprocity analogous to that between heat 

 and electricity in the ordinary thermo-current and Peltier's phe- 

 nomenon. 



If the forces set free by thermodiffusion appear mostly to be 

 trifling, yet it cannot be forthwith maintained that this pheno- 

 menon plays only a quite subordinate part in the economy of 

 nature; for the conditions of its occurrence may at least be 

 widely spread. 

 Davos, 26th December, 1872. 



VI. Determination of Degrees of Heat in Absolute Measure. 

 By L. Lorenz, of Copenhagen*. 



ONE of the most important means of modern times, for elu- 

 cidating the connexion between various forces indepen- 

 dently of all physical hypotheses, is the determination of the 

 magnitudes dependent on these forces by the same absolute 

 units. While the system of absolute measures has been carried 

 out in the sciences of magnetism and of electricity, the degree 

 of heat has only been determined arbitrarily; and thus, so to 

 speak, the thread has been broken which connects heat with the 

 other physical forces. The object of the present investigation is 

 to establish a definition of the absolute degree of heat in a purely 

 empirical manner, and by introducing it into science to illustrate 

 more clearly the relation in which heat and electricity stand to 

 each other. 



The absolute units introduced by Gauss and Weber, which we 

 shall use in the sequel, are the millimetre as unit of length, the 

 second as unit of time, and the milligramme as unit of mass. By 

 means of these units the electromagnetic unit of current -intensity 

 is denned as being the intensity of that current which, travers- 

 ing the unit of surface, acts upon a magnetic pole as an infi- 

 nitely small magnet whose moment is unity. Weber has further 

 defined the unit of the quantity of electricity as being that quan- 

 tity of positive electricity which in the unit of time moves, in 

 the direction of positive electricity, in a current whose intensity 

 is unity, it being presumed that the same quantity of negative 

 electricity is simultaneously transferred in the opposite direction. 

 In what follows we shall, in common with many other authors, 

 define the unit of electricity as being the sum of the quantities 

 of positive and negative electricity which, moving in opposite 

 directions through a circuit, produce the unit intensity of current. 

 * Translated from Poggendorff's Annalen, No. 11, 1872. 



