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Knight's Mechanical Encyclopedia (ed. Knight) 6 2 Browse Search
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Knight's Mechanical Encyclopedia (ed. Knight), A. (search)
to the power produced; and conversely, that when heat is produced by the expenditure of mechanical power, the quantity of heat produced bears a fixed proportion to the power expended. This law has been established chiefly by the experiments of Mr. Joule on the production of heat by the friction of the particles of various substances, solid, liquid, and gaseous, and he has ascertained the fixed proportion which heat and mechanical power bear to each other in cases of mutual conversion. The uits production, and produces by its disappearance, or, in other words, is equivalent to, 772 lbs. of mechanical power; that is, so much mechanical power as is sufficient to lift a weight of 1 lb. to a height of 772 feet. This quantity is known as Joule's equivalent, or the dynamical specific heat of water at ordinary temperatures. The dynamical specific heats of other substances may be determined by direct experiment, or by ascertaining the ratios to that of water. Thus, to heat 1 lb. of at
Knight's Mechanical Encyclopedia (ed. Knight), E. (search)
team-engines per pound of carbon or of coal equivalent to carbon. The price of zinc, however, being so much greater than that of coal, it is evident from these facts and calculations that electro-magnetic engines never can come into general use except in cases where the power required is so small that the cost of material consumed is of no practical importance, and the situation of the machinery is such as to make it very desirable to have a prime mover without a furnace. According to Mr. Joule, the consumption of a grain of zinc, though forty times more costly than a grain of coal, produces only about one eighth of the same mechanical effect. Cazal's electro-magnetic machine resembles a flywheel, being a thick disk of soft iron cut into the shape of a gear-wheel and having a circumferential groove wound with insulated wire, whose ends are soldered to insulated thimbles, which, by means of tangent springs, introduce the battery current. Surrounding this magnetic wheel is a
Knight's Mechanical Encyclopedia (ed. Knight), U. (search)
quid water, at about 39° Fah. The thermal unit of France is the quantity of heat which corresponds to an interval of 1° Centigrade in the temperature of 1 kilogramme of pure water at about 3.94° Centigrade. Rumford, in 1798, endeavored to ascertain the number expressing the precise relation between the functions of force and heat, known as the mechanical equivalent of heat. He used a solid plunger rotating against the bottom of an iron cylinder submerged in a box of water. Mayer and Joule farthered the experiment, the latter using paddle-wheels rotated in oil, mercury, or water by the force of a descending weight. The conclusions were, that the descent of 772 pounds 1 foot would raise the temperature of 1 pound of water 1° Fah.; therefore, 772 pounds = 1 unit of heat, and conversely, 1 unit of heat would produce a force of 772 foot pounds; consequently, 42.7 units of heat must be equal to 33,000 foot pounds = 1 horse-power. The London unit of illumination for photometric