High Temperatures. 317 



Besides, it is easy to prove, that this property belongs to two 

 platina wires of any diameter, but not formed of the same platina. 

 We first take a platina wire, and cut it in two, and we then pass 

 one of its halves through a wire-drawing machine, to diminish 

 its diameter. The two wires are then united together by twist- 

 ing together their ends. If we bring one of the joints to any 

 temperature, no electrical effect is manifested ; but if we melt a 

 fragment of the metal at one of the ends of the wire, there is 

 immediately a manifestation of the electrical current, and this 

 will happen whenever the circuit is formed of two wires which 

 do not proceed from the same platina. The least difference 

 in the platina of the two wires, is sufficient to give rise to an 

 electric current, when both are brought to the same tempera- 

 ture at the points of contact. I may remark, that the wires 

 were previously plunged in boiling nitric acid, so that we can- 

 not suppose that the preceding effects are owing to any foreign 

 substances adhering to their surfaces. 



It would appear, then, from these experiments, that the 

 more remote the melting point of metals is, the higher is 

 that temperature at which the ratio between the increase of 

 heat, and that of the electro-dynamic force ceases to be con- 

 stant ; but as the platina does not melt but at a very high 

 temperature, and as in feeble melting, the law of decrease is 

 not rapid, we may suppose, without any fear of committing 

 great errors, that, in the circuit of two platinum wires, which 

 do not proceed from the same metal, the constant ratio be- 

 tween the increments of heat, and the increments of the elec- 

 tro-dynamic intensity still exists at elevated temperatures, but 

 remote from their melting point. This property will now 

 enable us to express the temperatures of red heat in functions 

 of the degrees of the centigrade thermometer. 



As an application of the method which I am about to ex- 

 plain, I shall proceed to determine the temperature which the 

 two platina wires assume, (put together as above describ- 

 ed) when we place successively their points of junction in the 

 different cones of the flame of a spirit lamp. 



It is known that a flame in general, particularly that of a 

 taper, or spirit lamp, is formed of several unequal divisions, 

 of which we may easily distinguish four; the l.s7, which is at 



