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Updated: May 20, 2025
Calorific conductivity is due, in fact, to an exchange of electrons between the hot and the cold regions, the heated electrons having the greater velocity, and consequently the more considerable energy. The calorific exchanges then obey laws similar to those which govern electric exchanges; and calculation even leads to the exact values which the measurements have given.
It is to a German physicist, Giese, that we owe the first notions on the mechanism of the conductivity of gases, as we now conceive it. In two memoirs published in 1882 and 1889, he plainly arrives at the conception that conduction in gases is not due to their molecules, but to certain fragments of them or to ions.
Why principally the negative flame returns may be explained in two ways either the point of the flame loses much by radiation, or the base of the flame is a bad conductor. The former explanation would agree with the experiments made by Wiedemann and Ruhlmann, the latter with Erdman's theory of unipolar conductivity of flames.
Such a surface, therefore, is always an equipotential. In the language of alchemy, conductivity is a mercurial property. In the presence of such a body, therefore, no Salt-Sulphur contrasts can obtain. In view of what we found above as the mean position of the metals in the alchemic triad, it is significant that they, precisely, should play so outstanding a role as electrical conductors.
The varying conductivity of the different strata in relation to heat and electricity may have been an important factor. Trap dikes frequently enrich veins where they approach or intersect them, and they have often been the primum mobile of vein formation, but chiefly, if not only, by supplying heat, the mainspring of chemical action.
It has allowed us to show, as M. Brillouin has done, that the coefficient of diffusion of two gases does not depend on the proportion of the gases in the mixture; it gives a very striking image of the phenomena of viscosity and conductivity; and it leads us to think that the coefficients of friction and of conductivity are independent of the density; while all these previsions have been verified by experiment.
The gas, which till then has behaved as a perfect insulator, suddenly acquires a remarkable conductivity.
Between the two points in question there are, first, the material media such as the air, the earth, and the water. For a long time we have used for transmissions to a distance the elastic properties of the air, and more recently the electric conductivity of the soil and of water, particularly that of the sea.
More directly, as an antecedent to the discovery, should be quoted the remark made by Varley in 1870, that coal-dust changes in conductivity when the electromotive force of the current which passes through it is made to vary.
The reversed currents are, then, arrested during their passage; and, in order to collect them, it becomes necessary to considerably diminish the gaseous pressure of the aeriform conductor interposed in the discharge; to increase its conductivity; or to open to the current a very resistant metallic derivation.
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