214 Prof. Thomson on the Dynamical Theory of Heat. 



parts of pure bismuth. This result may be taken, I feel satisfied, 

 as the correct ratio upon which to base calculations in the esti- 

 mation of bismuth. Upon this datum the standard solutions pre- 

 viously described are prepared. 



In conclusion I may say, that the method I propose for the 

 determination of bismuth recommends itself by the accuracy of 

 its results, facility of execution, and neatness of manipulation, 

 joined to the permanency of the test-agent employed. 



Dr. Angxis Smith's Laboratorj', 



Grosvenor Square, Manchester. 



XXVII. On the Dynamical Theory of Heat.— VQ.viYl. Thermo- 

 electric Currents. By William Thomson, M.A., Professor 

 of Natural Philosophy in the University of Glasgow"^. 

 [Continued from vol. ix. p. 531.] 

 Preliminary §§ 97-101. Fundamental Principles of General 



Thermo-dynamics recapitulated. 

 97. 1% /TECHANICAL action may be derived from heat, and 

 lYX heat may be generated by mechanical action, by 

 means of forces either acting between contiguous parts of bodies, 

 or due to electric excitation ; but in no other way known, or 

 even conceivable, in the present state of science. Hence thermo- 

 dynamics falls naturally into two divisions, of which the subjects 

 are respectively, the relation of heat to the forces acting between 

 contiguous parts of bodies, and the relation of heat to electrical 

 agency. The investigations of the conditions under which 

 thermo-dynamic efi"ects are produced, in operations of any fluid 

 or fluids, whether gaseous or hqvxid, or passing from one state 

 to the other, or to or from the solid state, and the establishment 

 of universal relations between the physical properties of all sub- 

 stances in these difi'erent states, which have been given in Parts 

 I.-V. of the present series of papers, belong to that first great 

 division of thermo-dynamics — to be completed (as is intended 

 for future communications to the Royal Society) by the exten- 

 sion of similar researches to the thermo-elastic properties of 

 solids. The second division, or thermo-electricity, which may 

 include many kinds of action as yet undiscovered, has hitherto 

 been investigated only as far as regards the agency of heat in 

 producing electrical efi'ects in non-crystalline metals. In a 

 mechanical theory of electric currents, communicated to the 

 Royal Society, Dec. 15, 1851 f, the application of the general 



* From the Transactions of the Royal Society of Edinburgh, vol. xxi. 

 part 1 ; read 1st May, 1854. 



t See 'Proceedings' of that date, or Philosophical Magazine, 1852, 

 where a sufficiently complete account of the investigations and principal 

 results is given. 



