62 W. A, Norton on Molecular Physics. 
than antimony, and in fact than most other metals, and hence 
its surface molecules should imbibe and retain more heat than 
those of the antimony. The diamagnetic properties of bismuth 
also indicate, as will be seen hereafter, that its molecular atmos- 
pheres are remarkably expansible. If these peculiarities of bis- 
muth be admitted, we have an explanation of the fact that bis- 
muth is positive’ to other metals in its thermo-electric relations. 
The bismuth and antimony in the thermo-electric pair, it will be 
observed, hold the same relation to each other as the zinc and 
copper in the galvanic pair, and the heat does the same electri- 
eal duty in the one, that the oxygen does in the other. 
If the other ends of the two metals be brought together and 
led, the current will be reénforced, since the molecular at- 
mospheres of the bismuth will contract more than those of the 
antimony. (See effect of cold, p. 61.) 
It has been ascertained as the result of numerous experiments, 
that “increasing the temperature of the negative metal gener- 
ally increases the amount of deflection of the galvanometer 
needle produced by heating the junetion; while if the higher 
heat is applied to the metal which is positive at moderate tem- 
ratures, a current in the opposite direction is established.” To 
get at the explanation of these curious effects we must observe 
that the “ higher heat” spoken of is applied at a certain distance 
from the junction, and hence it is the inner sides of the surface 
molecules which first receive the heat from this second source, 
become positively polarized. Accordingly, the current should 
be strengthened in the first case, above mentioned, and weak- 
ened in the second. It has also been observed that a current 
may be excited with two wires of the same metal, by heating 
the end of one and bringing it in contact with the other; and 
that the direction of the current at the junction is from the cold 
to the hot wire.” In this case it is to be remarked that the hot 
wire is in the act of cooling, and hence there should be an elec- 
tric movement toward its surface (p. 61), or from the cold to 
the hot wire, through the junction. 
yro-electric tals—Tourmaline is the most conspicuous 
erystal belonging to thisclass. ‘A prism of tourmaline has dif- 
ferent secon planes at its two extremities, or, as it is ex- 
= is hemihedrally modified.” This peculiarity of crystal- 
erystal have different mechanical properties on opposite sides. 
n this condition of things we may reasonably suppose that the 
ecular atmospheres would expand unequally on opposite 
that which imparts, at the heated junction, 
This is often termed the negative . 
electrical state is negative (p, 245). 
