Davis's manual of magnetism : including galvanism, magnetism, electro-magnetism, electro-dynamics, magneto-electricity, and thermo-electricity . Where the same metal, in different con-ditions, is used, the production of electricity is re-ferred to the unequal propagation of heat on eachside of the heated point, caused in the single wire bythe obstruction occasioned by the twist, and in thecase of two wires, by the contact of the cold wire, orwhere they are connected together, by the differencein their diameters. The causes, however, have notyet been fully investigated, and many points are in-v
Davis's manual of magnetism : including galvanism, magnetism, electro-magnetism, electro-dynamics, magneto-electricity, and thermo-electricity . Where the same metal, in different con-ditions, is used, the production of electricity is re-ferred to the unequal propagation of heat on eachside of the heated point, caused in the single wire bythe obstruction occasioned by the twist, and in thecase of two wires, by the contact of the cold wire, orwhere they are connected together, by the differencein their diameters. The causes, however, have notyet been fully investigated, and many points are in-volved in great obscurity. 110. Metals differ greatly in their power to excitea current, when associated together in thermo-electricpairs. Some of the peculiarities in the combina-tions of the more useful metals will be stated. It isnecessary, however, to say a few words with regardto the galvanometer, an instrument to indicate ormeasure electrical currents, and which will be morefully described in Book I. Chapter 2. A currentof electricity, passing through a wire, is found to de-flect a magnetic needle in its neighborhood. By an Fig. arrangement such as Fig. 39, where G is the gal-vanometer, consisting of a magnetic needle in close 70 DAVISS MANUAL. proximity to a coil of wire, above which is fixed agraduated circle, the direction of an electrical currentmade to pass through the wire is indicated by thedeflection of the needle from the north and southline, in one direction or the other, and its strengthis measured by the number of degrees to which itis deflected. The deflection of the needle will befrequently referred to hereafter. When using thisinstrument, the zero points of the graduated circlemust be placed north and south, so as to lie in thesame direction as the magnetic needle above themdoes when influenced by the earths magnetism the figure, a thermo-electric pair, of bismuth andantimony, heated by a spirit-lamp, is shown inconnection with the galvanometer
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Keywords: ., bookcentury1800, bookdecade1850, booksubjectmagnetism, bookyear18
