154 PROFESSOR W. THOMSON ON THE 
magnetization; and may be said to be inductively crystalline. Or again, minute 
fragments of non-crystalline substances may be put together, so as to constitute 
solids, which, on a large scale, possess the general characteristic of homogeneous 
crystalline substances; and such bodies may be said to possess the crystalline 
characteristic by structure, or to be structurally crystalline. 
148. As regards thermo-electric currents, the characteristic of crystalline sub- 
stance must be, that bars cut from it in different directions would, when treated 
thermo-electrically as linear conductors, be found in different positions in the 
thermo-electric series; or that two bars cut from different directions in the sub- 
stance would be thermo-electrically related to one another like different metals. 
This property has been experimentally demonstrated by SvanBERG, for crystals of 
bismuth and antimony; and there can be no doubt but that other natural metallic 
crystals will be found to possess it. I have myself observed, that the thermo- 
electric properties of copper and iron wires are affected by alternate tension and 
relaxation in such a manner, as to leave no doubt but that a mass of either 
metal, when compressed or extended in one direction, possesses different thermo- 
electric relations in different directions. Fragments of different metals may be 
put together so as to form solids, possessing by structure the thermo-electric 
characteristic of a crystal, in an infinite variety of ways. Thus, a structure con- 
sisting of thin layers alternately of two different metals, possesses obviously the 
thermo-electric qualities of a crystal with an axis of symmetry. I have inves- 
tigated the thermo-electric properties in all directions of such a structure, in terms 
of the conducting powers for heat and electricity, and the thermo-electric powers, 
of the two metals of which it is composed; and bars made up of alternate layers 
of copper and iron, one with the layers perpendicular, another with the layers 
oblique, and a third with the layers parallel, to the length, illustrating the theo- 
retical results, which were communicated along with this paper, were exhibited to 
the Royal Society. The principal advantage of considering metallic structures 
with reference to the theory of thermo-electricity is, as will be seen below, that 
we are so enabled to demonstrate the possibility of crystalline thermo-electric 
qualities of the most general conceivable type, and are shown how to construct solids 
(whether or not natural crystals may be ever found) actually possessing them. 
149. The following two propositions with reference to thermo-electric effects 
in a particular case of crystalline matter are premised to the unrestricted treat- 
ment of the subject, because they will serve to guide us as to the nature of the 
agencies for which the general mathematical expressions are to be investigated. 
Prop. I. If a bar of crystalline substance, possessing an axis of thermo-electric 
symmetry, has its length oblique to this axis, a current of electricity sustained in 
it longitudinally will cause evolution of heat at one side, and absorption of heat 
at the opposite side, all along the bar, when the whole substance is kept at the 
same temperature. 
NS wen Age 
