This will be composed of a conduction and a convection current, the latter due to rising or falling air currents carrying ions.
A closed stove acts mainly by convection; though when heated to a high temperature it gives out radiant heat.
Since the only cause for these convection currents is the statical instability produced by radiation, and the rapid stifling of radiations within the body produces there a temperature gradient falling very slowly, they would be for the most part extremely slight.
The potential diagrams already given have been drawn on this assumption, that the Thomson effect is not really due to convection of heat by the current, but is the measure of an E.M.F.
In the vast majority of cases the bacilli are in the lymphatic or the circulatory system, and aerial convection, even for a short distance, seems highly improbable.
Ann., 1875), who regarded electricity as consisting of atoms much smaller than those of matter, and supposed that heat was the kinetic energy of these electric atoms. If we suppose that an electric current in a metal is a flow of negative electric atoms in one direction, the positive electricity associated with the far heavier material atoms remaining practically stationary, and if the atomic heat of electricity is of the same order as that of an equivalent quantity of hydrogen or any other element, the heat carried per ampere-second at o C., namely P, would be of the order of 030 of a joule, which would be ample to account for all the observed effects on the convection theory.
Wilson considers that convection currents in the upper atmosphere would be quite inadequate, but conduction may, he thinks, be sufficient alone.
The quantity of heat liberated by convection as the current flows from hot to cold is represented in the equation by dP=d(pT).
Lead, in which one junction is at o° C. and the other at t° C. For this reason the potential diagrams on the convection theory are more simple and useful than those on the contact theory.
It is not difficult in such compact species to distinguish between superficial cells, whose chief function is assimilation, subjacent cells charged with reserve material, and a core of tissue engaged in the convection of elaborated material from part to part.
In measuring conduction of heat in fluids, it is possible to some extent to eliminate the effects of molar convection or mixing, but it would not be possible to distinguish between diffusion, or internal radiation, and conduction.
Indeed it seems that, in the final distribution of density throughout the part which is not subject to violent convection currents, it must increase slightly from the centre outwards, since the currents would cease altogether as soon as 'a uniform state was restored.
- The idea of convection of heat by an electric current, and the phrase " specific heat of electricity " were introduced by Thomson as a convenient mode of expressing the phenomena of the Thomson effect.
Because the surface layers of water are too light, on account of the low salinity due to ice-melting, to enable even the cold of a polar winter to set up a downward convection current.
Ice forms over fresh water if the temperature of the air has been for a sufficient time at or below the freezing-point; but not until the whole mass of water has been cooled down to its point of maximum density, so that the subsequent cooling of the surface can give rise to no convection currents, is freezing possible.
Before 1868 Maxwell conducted the experiment by sending light from the illuminated cross-wires of an observing telescope forward through the object-glass, and through a train of prisms, and then reflecting it back along the same path; any influence of convection would conspire in altering both refractions, but yet no displacement of the image depending on the earth's motion was detected.
These conditions cannot be consistent with sensible convection of the aether near the earth without involving discontinuity in its motion at some intermediate distance, so that we are thrown back on the previous theory.
The convection of a medium thus polarized involves electric disturbance, and therefore must contribute to the true electric current; the determination of this constituent of the current is the most delicate point in the investigation.
The establishment and convection of a single polar atom constitutes in fact a quasi-magnetization, in addition to the polarization current as above defined, the negative poles completing the current circuits of the positive ones.
He also determined the effect of change of temperature distribution on the rate of generation of heat by the current; and on the external loss of heat by radiation, convection and conduction.
Is due entirely to change of substance (dP - Tdp); on the convection theory, it is due entirely to change of temperature (pdT).
Corresponding diagrams for the same metals on the convection theory are given in fig.
The polarization itself is determined from the electric force (P,Q,R) by the usual statical formula of linear type which becomes tor an isotropic medium (.f',g',h') = c2(P,Q,R), because any change of the dielectric constant K arising from the convection of the material through the aether must be independent of the sign of v and therefore be of the second order.
If v varies with respect to locality, or if there is a velocity of convection (p,q,r) variable with respect to direction and position, and analytical expression of the relation (ii) assumes a more complex form; we thus derive the most general equations of electrodynamic propagation for matter treated as continuous, anyhow distributed and moving in any manner.
It ascends the flow pipe by convection, where its onward journey would speedily end if it were not for the driving force of other molecules of water following, and the suction set up by the gravitation into the boiler of the cooled water by the return pipe.
Bouchotte have 1 See Lord Kelvin, Reprint of Papers on Electrostatics and Magnetism (1872);" Electrophoric Apparatus and Illustrations of Voltaic Theory,"p. 319;" On Electric Machines Founded on Induction and Convection,"p. 330;" The Reciprocal Electrophorus,"P. 337.
The presence of phycocyanin, phyco a role in the morphological development of land plants is entirely wanting in algae, such conducting tissues as do exist in the larger Phaeophyceae and Rhodophyceae serving rather for the convection of elaborated organic substance, and being thus comparable with the phloem of the higher plants.
Reynolds, in his investigation, introducing no new form of law of distribution of velocities, uses a linear quantity, proportional to the mean free path of the gaseous molecules, which he takes to represent (somewhat roughly) the average distance from which molecules directly affect, by their convection, the state of the medium; the gas not being uniform on account of the gradient of temperature, the change going on at each point is calculated from the elements contributed by the parts at this particular distance in all directions.
Any convection of that medium could be tested by the change of effective velocity of light, which would be revealed by a prism as was suggested by F.
In this place it must suffice to indicate the gist of the more recent developments of the electro-optical theory, which involve the dynamical verification of Fresnel's hypothesis regarding optical convection and the other relations above described.
True electric current arises solely from convection of the atomic charges or electrons; this current is therefore not restricted as to form in any way.