PROFESSOR THOMSON ON THE ELECTRO-DYNAMIC QUALITIES OF METALS. 651 
3. All properties, then, of electric and thermal conductivity, of magnetic inductive 
capacity and retentiveness, and of thermo-electric rank and its variations from one 
temperature to another, may be characterized as electro-dynamic ; and the degrees 
to which these properties are possessed by different substances may be called their 
electro-dynamic qualities. Again, the variation which absolute magnetic inductive 
capacity, and magnecrystallic axial differences, experience with change of tempe- 
rature may obviously be made the means of a transformation of heat into common 
mechanical energy, and we have thus a set of magneto-dynamic properties of matter 
which may almost in the present state of science be regarded as intrinsically electric, 
but which at all events (when we consider that the motions contemplated, taking 
place as they do under magnetic force, cannot but be accompanied by electric 
currents) may be fairly classed under the general designation of electro-dynamic. 
The variations of intrinsic magnetism, of magnetic inductive capacity, and of magne- 
crystallic properties, produced by variations of temperature, are therefore included 
among the electro-dynamic qualities of metals which I propose to investigate, although 
I have as yet made no progress in this branch of the subject. 
PART I. ON THE ELECTRIC CONVECTION OF HEAT. §§ 4 to 77. 
4 to 18. Theoretical Indications. 
4 to 9. Origin of the Investigation. 
4. In first attempting an application of the principles of the Dynamical Theory of 
Heat to show the mechanical relation between cause and effect in thermo-electric 
currents, I supposed the effects thermal and mechanical that can be produced by a 
thermo-electric current in any part of its circuit to be, as first suggested by Joule, 
due to the heat absorbed, according to Peltier’s discovery, at the liot junction in 
virtue of the current crossing it, and I pointed out that the current crossing the cold 
junction must evolve a quantity of heat which, were this supposition true, would be 
less than that absorbed at the hot junction, by an amount precisely equivalent to all 
the effects, produced by the current in the rest of the circuit*. 
5. Introducing Carnot’s principle, as modified in the Dynamical Theory of 
another is electricity set into a state of motion ; that this electric motion subsides wholly into heat in most 
cases, either close to its origin and instantaneously, as when the solids are both of metal, or at sensible distances 
from the actual locality of friction and during appreciable intervals of time, as when the substance of one or both 
the bodies is of low conducting power for electricity ; and that it only fails to produce the full equivalent in 
heat for the work spent in overcoming the friction, when the electric currents are partially diverted from closed 
circuits in the two bodies and in the space between them, and are conducted away to produce other effects in 
other localities. Still, no hypothesis need be implied by using the expression “ the frictional generation of 
heat by an electric current,” as defined in the passage quoted, and it is introduced into the present paper with 
no other justification than its convenience. 
* Dynamical Theory of Heat, March 17, 1851, § 17. 
MDCCCLVI. 4 R 
