The London, Edinburgh and Dublin philosophical magazine and journal of science . was probably Montanacopper. Commercial Hard-drawn Copper Wire.—This was from alot purchased for electrical testing purposes, which showed aspecific resistance of 0*1440 international ohm per metre-gram, or an electrical conductivity of about 983 per cent,referred to Matthiessens copper. Methods and Apparatus.—The method consists in measuringthe thermal electromotive force of a couple composed of onewTire of platinum and the other of a- iO-per-cent. rhodo-platinum alloy. One junction is immersed in the melting or M
The London, Edinburgh and Dublin philosophical magazine and journal of science . was probably Montanacopper. Commercial Hard-drawn Copper Wire.—This was from alot purchased for electrical testing purposes, which showed aspecific resistance of 0*1440 international ohm per metre-gram, or an electrical conductivity of about 983 per cent,referred to Matthiessens copper. Methods and Apparatus.—The method consists in measuringthe thermal electromotive force of a couple composed of onewTire of platinum and the other of a- iO-per-cent. rhodo-platinum alloy. One junction is immersed in the melting or Melting-points of Aluminium, Silver, Gold, Copper, fyc. 39 solidifying metal, and the other surrounded by ice. The wirewas that furnished by Carpentier, of Paris (through Queen &Co., of Philadelphia), with the Le Chatelier pyrometer. The was measured in microvolts (international) bythe Poggendorff null method modified for rapid and con-venient working. The disposition of apparatus is shown infig. 1. B is a battery of sufficiently steady (A single Fig. Samson-Leclauche cell was entirely satisfactory.) In directcircuit with this were two water rheostats, W, in series ; anammeter, A, which was a Weston voltmeter (No. 395) withthe calibrating coil only in use ; and a manganine wire resist-ance, a,b, c, d, divided into sections, each of accurately knownresistance. T is the thermo-couple connected through a sen-sitive galvanometer, G, and key to any desired sections of thecoil a, b, c, d. The water rheostats were of about 100 ohmsand 8 ohms respectively, and the vertical motion of theirplungers thus served to give a coarse and fine adjustment tothe resistance in the circuit. The current could thus bepromptly and closely adjusted. The voltmeter was one ofthe type having a calibrating coil; that is, one having aconnexion by means of which the usual high resistance seriescoil could be cut out, leaving its resistance about 117 of the Weston voltmeters with a
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Keywords: ., bookcentury1800, bookdecade1840, bookidlondon, booksubjectscience
