An international system of electro-therapeutics : for students, general practitioners, and specialists . or the iron a wire of pure silver—which is the best metallic Fig. 1. conductor—be substituted, the copper, as it offers a greater resistance,will become heated. 3. If a chain of three or more wires of silver and platinum, or copperand platinum, alternately arranged, be interposed in the circuit, theplatinum may become almost incandescent, while the silver and copperwill be barely, if at all, warm. 4. If two platinum wires of the same length, but different in thick- P^~!nnnr FlG. 2. ness, be
An international system of electro-therapeutics : for students, general practitioners, and specialists . or the iron a wire of pure silver—which is the best metallic Fig. 1. conductor—be substituted, the copper, as it offers a greater resistance,will become heated. 3. If a chain of three or more wires of silver and platinum, or copperand platinum, alternately arranged, be interposed in the circuit, theplatinum may become almost incandescent, while the silver and copperwill be barely, if at all, warm. 4. If two platinum wires of the same length, but different in thick- P^~!nnnr FlG. 2. ness, be introduced,—one being, say, one-fiftieth of an inch in diameter andthe other twice as thick, or one-twentj^-fifth of an inch, and placed parallelto each other in the circuit (Fig. 1),—the larger of the two, which trans-mits the greater quantity of electricity and presents a cooling surfacemuch less in proportion to its volume than the finer wire, wiU have a moreelevated temperature while thus united ; but if these same wires areunited end to end, the finer wire will become red-hot (Fig. 2),. Fig. 3. 5. If a platinum wire—say, one-thirtieth of an inch in diameter andtwelve inches long—be brought to a dull cherry-red heat, and a streamof cold water be made to flow over a space of two or three inches of itscentre, the wire on either side of the cool portion will become incan- L-6 BYRNE. descent (Fig. 3). This experiment proves what the laws of electricconductivity teach : that while heat in any part of a metallic conductorincreases its resistance, by cooling a part of the wire—say, one-third—the latter becomes a better conductor, and most of the current, at firstdistributed over the entire length, is now employed in heating two-thirdsonly. 6. In further illustration of the electro-physical laws of resistanceand conductivity, if, as in the previous experiment, the wire be broughtto a red heat, and jvhile in this condition the flame of a spirit-lamp bemade to play u
Size: 2079px × 1202px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, booksubjectuterus, bookyear1894
