The other pair of platinum wires are connected by a tellurium-bismuth thermo-couple, the junction of which just makes contact with the centre of the fine wire.
In the article Thermo Chemistry a general account of heats of formation of chemical compounds is given, and it is there shown that this constant measures the stability of the compound.
Among other subjects at which he subsequently worked were the absorption of gases in blood (1837-1845), the expansion of gases by heat (1841-1844), the vapour pressures of water and various solutions (1844-1854), thermo-electricity (1851), electrolysis (1856), induction of currents (1858-1861), conduction of heat in gases (1860), and polarization of heat (1866-1868).
The dimensions of a piece of iron, for example, its elasticity, its thermo-electric power and its electric conductivity are all changed under the influence of magnetism.
Abrupt alterations, take place in its density, specific heat, thermo-electric quality, electrical conductivity, temperature-coefficient of electrical resistance, and in some at least of its mechanical properties.
The temperature was determined by a platinum-rhodium and platinum thermo-j unction in contact with the metal.
It is remarkable that if a flow of heat be substituted for a current of electricity a closely allied group of " thermo-magnetic effects " is presented.
Attempts have been made to explain these various effects by the electron theory.4 Thermo-electric Quality.-The earliest observations of the effect of magnetization upon thermo-electric power were those of W.
The curves given by Houllevigue for the relation of thermo-electric force to magnetic field are of the same general form as those showing the relation of change of length to field.
Rhoads obtained a cyclic curve for iron which indicated thermo-electric hysteresis of the kind exhibited by Nagaoka's curves for magnetic strain.
Bidwell," who, adopting special precautions against sources of error by which former work was probably affected, measured the changes of thermo-electric force for iron, steel, nickel and cobalt produced by magnetic fields up to I Soo units.
In the case of iron and nickel it was found that, when correction was made for mechanical stress due to magnetization, magnetic change of thermo-electric force was, within the limits of experimental error, proportional to magnetic change of length.
Further, it was shown that the thermo-electric curves were modified both by tensile stress and by annealing in the same manner as were the change-of-length curves, the modification being sometimes of a complex nature.
In the case of cobalt no such relation could be traced; it appeared that the thermo-electric power of the unmagnetized with respect.
The sign of the thermo-electric effect for nickel, as given by Rhoads, is incorrect.
[[[Feebly Susceptible Substances]] different specimens were tested, all of which became, like iron, thermo-electrically positive to the unmagnetized metals.
As to what effect, if any, is produced upon the thermo-electric quality of bismuth by a magnetic field there is still some doubt.
Van Aubel I believes that in pure bismuth the thermo-electric force is increased by the field; impurities may neutralize this effect, and in sufficient quantities reverse it.
Hall proposed to overcome this difficulty by coating the plate thickly with copper on both sides, and deducing the difference of temperature between the two surfaces of junction of the iron and the copper from the thermo-electric force observed by means of a number of fine copper wires attached to the copper coatings at different points of the disk.
The advantage of the thermo-junction for this purpose is that the distance between the surfaces of which the temperature-difference is measured, is very exactly defined.
The disadvantage is that the thermo-electric force is very small, about ten-millionths of a volt per degree, so that a small accidental disturbance may produce a serious error with a difference of temperature of only 1° between the junctions.
The actual tempera ture of the metal itself can then be observed by inserting thermometers or thermo-couples at measured distances from the centre.
Trans., 1892), with the substitution of thermo-couples (following Wiedemann) for mercury thermometers.
The temperature at different heights was measured by iron wires forming thermo-junctions with the mercury in the inner tube.
It was also tacitly assumed that the thermo-electric power of the couples for the gradient was the same as that of the couples for the mean temperature, although the temperatures were different.
Duncan, the thermo-electric method, devised by Kohlrausch, and applied by W.
The chief difficulty is that of measuring the small change of resistance accurately, and of avoiding errors from accidental thermo-electric effects.
(b) The method of Kohlrausch, as carried out by Jaeger and Dieselhorst (Berlin Acad., July 1899), consists in observing the difference of temperature between the centre and the ends of the bar by means of insulated thermo-couples.
Surrounded By A Nickel Plated Steel Enclosure B, Forming The Bulb Of A Mercury Thermo Regulator, Immersed In A Large Water Bath Maintained At A Constant Temperature.
James Cumming (1777-1861) in 1823 (Annals of Philosophy, 1823) found that the thermo-electric series varied with the temperature, and J.
Ohm verified his law by the aid of thermo-electric piles as sources of electromotive force, and Davy, C. S.
His work on the electrodynamic qualities of metals, thermo-electricity, and his contributions to galvanometry, were not less massive and profound.
He concluded that the gases are due to the decomposition of an organic colouring matter, which has, however, no connexion with the fluorescence or thermo-luminescence of the mineral.
Many kinds of fluor-spar are thermo-luminescent, i.e.
In 1845 he showed, by means of a thermo-galvanometer, that the solar spots radiate less heat than the general solar surface (Proc. Am.