TEMPERATURES CALCULATED FROM QUANTITIES OF ELECTRICITY. 



TABLE II. 



93 



344. We are therefore led to the general conclusion that, in these six different sys- 

 tems of metals, the developments of electricity do not increase proportionally with the 

 temperatures, but in some with greater rapidity, and in others with less. 



345. The results here given I have corroborated in a variety ot ways, and with a 

 variety of wires. A pair, consisting of copper and platina, gave for the temperature of tin, 

 when in the act of congealing, 452 Fahr. instead of 442 Fahr., the point usually taken. 

 For the melting point of lead, it gave 942^ Fahr., instead of 612 Fahr. The melt- 

 ing points of tin, lead, zinc, and occasionally of antimony and bismuth, were in this 

 manner employed, for they allow time for the working of the torsion balance, and, with 

 the exception of bismuth, their temperature appears to be steady all the while they are 

 in a granular condition, before they finally solidify. The action of these metals on the 

 thermo-electric pair is easily prevented by dipping it into a cream of pipe-clay. 



346. A pair of copper and platina gave for a dull red heat 1416 Fahr., and for a 

 bright red 2103 Fahr. 



347. A pair of palladium and platina gave for a dull red 1850 Fahr., and for a bright 

 red 2923 Fahr. 



348. Some of the combinations into which iron enters as an element give rise to 

 remarkable results ; thus, if we project the curve given by a system of copper and iron, 

 we shall find it resembling^," 1 . 33, where the maximum ordinate b occurs at a tempera- 

 ture of about 650 Fahr. ; the point c appears to be given between 700 and 800 degrees ; 

 d by a dull red heat ; e is very nearly the point at which an alloy of equal parts of brass 

 and silver melts, for if the pair be soldered with this substance, it fuses when the needles 

 have returned almost exactly to the zero point. With harder solders, or with wires 

 simply twisted, the curve may be traced on the opposite side of the axis towards^ its 

 ordinate increasing with regularity. At 60 Fahr., taking the length of the ordinate 

 corresponding to a temperature of 212 Fahr. as unity, the length of the maximum or- 

 dinate at b is 1-85, very nearly. 



349. A system of silver and iron gives also a similar curve, the point b occurring at 

 a temperature rather higher than the analogous one for the preceding system, but still 

 below the boiling point of mercury. 



350. Now all these things serve to show that we cannot determine with accuracy 

 unknown temperatures by the aid of thermo-electric currents, on the supposition that 

 the increments of the quantities of electricity are proportional to the increments of 

 temperature throughout the range of the mercurial thermometer. 



351. Let us now proceed to the second proposition, " That the tension undergoes a 

 slight increase with increase of temperature, a phenomenon due to the increased resist- 

 ance to conduction of metals when their temperature rises." 



