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Heat excited, concentrated into a certain point of a solid body, communicates itself by way of conduction, first to the particles nearest the heated point, then gradually to all the regions of the body. Whence the problem of which the following is the enunciation.
They are charged like the particles of the insulator, but they discharge with greater ease and rapidity; and this rapidity of molecular discharge is what we call conduction. Conduction then is always preceded by atomic induction; and when, through some quality of the body which Faraday does not define, the atomic discharge is rendered slow and difficult, conduction passes into insulation.
A given area of ground, as estimated by the every-day rule of measurement in yards or acres, presents always the same apparent quantity of absorbing, radiating, and reflecting surface; but the real extent of that surface is very variable, depending, as it does, upon its configuration, and the bulk and form of the adventitious objects it bears upon it; and, besides, the true superficies remaining the same, its power of absorption, radiation, reflection, and conduction of heat will be much affected by its consistence, its greater or less humidity, and its color, as well as by its inclination of plane and exposure.
This is evidently a point in which the action of the forest may be expected to differ from that of the meadow or naked earth; for though, of course, inferior strata tend to a certain extent to follow somewhat the same course as the mass of inferior leaves, they do so to a less degree conduction, and the conduction of a very slow conductor, being substituted for radiation.
Before I could reply there came a scuffling sound from the bank above us, and the snapping of branches and twigs. It was Mr. Cooke. His descent, the personal conduction of which he lost half-way down, was irregular and spasmodic, and a rude concussion at the bottom knocked off a choice bit of profanity which was balanced on the tip of his tongue.
The vacuum wall is to protect the occupants of the ship against any undue heat. If we should get within the atmosphere of a sun, it would be disastrous if the physical conduction of heat were permitted, for though the relux will turn out any radiated heat, it is a conductor of heat, and we would roast almost instantly. These artificial metals are both absolutely infusible and non-volatile.
Before I could reply there came a scuffling sound from the bank above us, and the snapping of branches and twigs. It was Mr. Cooke. His descent, the personal conduction of which he lost half-way down, was irregular and spasmodic, and a rude concussion at the bottom knocked off a choice bit of profanity which was balanced on the tip of his tongue.
When the crust was more highly heated, the radiation and conduction must have been proportionately more rapid. Owing to this cause also the contraction of the crust was accelerated.
We'll be cooled by conduction and convection." As the others got the suits ready, he lowered the ship gently to the snowy ground. It sank into nearly ten feet of snow. He turned on the powerful searchlight, and swept it around the ship. Under the warm beams, the frozen gasses evaporated, and in a few moments he had cleared the area around the ship. Morey and the others came back with their suits.
The question has been ably discussed by Beraud in the Revue des Deux Mondes for April, 1870, the result being that the drying of the soil by pines is due simply to conduction by the roots, whatever may be the foliage of the tree. See post: Influence of the Forest on Flow of Springs. The Forest in Winter.
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