MKMOIR XXIV.] THE ELECTRO-MOTIVE POWER & H^T. v<29 



ture appears to be steady all the while they "' 

 granular condition before they finally solidify, 

 tion of these metals on the thermo-electric pair is easily^ 

 prevented by dipping it into a cream of pipe-clay. ' / 



A pair of copper and platinum gave for a dull red 

 heat 1416 Fahr., and for a bright red 2103 Fahr. 



A pair of palladium and platinum gave for a dull red 

 1850 Fahr., and for a bright red 2923 Fahr. 



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 

 w r e shall find it resem- 

 bling Fig. 54, where 

 the maximum ordinate 

 b occurs at a temper- 

 ature of about 650 Ficr>54 

 Fahr. ; the point c ap- 

 pears 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 ordinates increasing with regularity. At 

 60 Fahr., taking the length of the ordinate correspond- 

 ing to a temperature of 212 Fahr. as unity, the length 

 of the maximum ordinate at b is 1.85, very nearly. 



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. 



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 



