220 Mr. W. H. Steele's Thermoelectric Diagram 



for example), a deflexion of a scale- division or two was always 

 observed on closing K 2 . This deflexion generally increased 

 while observation was going on, chiefly from Peltier effects 

 in r. This deflexion having been mentally noted, w was 

 thrown out and e put in, K x and K 2 closed, and R adjusted till 

 the deflexion was the same as that observed previously. Then 

 efE is equal to r/(R + r-\-$lb), E 6 being the internal resistance 

 of E. I used the Clark cell, as it had been recommended by 

 Prof. Threlfall (Phil. Mag. 1889, vol. xxviii.) as a good source 

 of small constant currents. I made three according to Lord 

 Eayleigh's instructions, and on testing them found that they 

 gave consistent results when closed through resistances of not 

 less than 6000, 5000, and 4000 ohms respectively. That is, # the 

 values of the internal resistance from any two observations 

 with resistances higher than those mentioned were consistent, 

 but began to vary when the cells were closed through less 

 resistances. But after being closed through lower resistances, 

 they quickly recovered on being left on open circuit. The 

 resistances of the cells were 265, 43, and 50 ohms. In my 

 observations I never used more than two thirds of the current 

 that I might have as determined above, and when I wished to 

 have a greater current (as was necessary in working with 

 antimony) I put the three cells in parallel and closed through 

 3800 ohms. __ 



When copper was one of the metals forming the pair under 

 examination, the junctions of the copper with the two ends of 

 the other metal, generally a wire, were immersed in beakers 

 of oil, the junction formed by twisting the wires together 

 being wrapped round the bulbs of the thermometers. When 

 copper was not one of the pair, then the one junction was in 

 a beaker of hot oil as before, and the two junctions of copper 

 with the two other metals were kept in the same beaker of 

 oil, insulation being of course attended to. By observing the 

 temperatures of the hot and cold junctions on each occasion, 

 it was not necessary to take any precautions to keep the cold 

 junction at a constant temperature, as the- correction to be 

 applied was determined from each set of observations. 



I did not go higher than 100° C. in observing, as I had 

 shown (Proc. Roy. Soc. Victoria, 1893) that at high tempera- 

 tures the ordinary thermoelectric formulae fail, and occa- 

 sionally I noticed irregularities coming in even at .100° C. 

 In the paper quoted I have described some months' experi- 

 ments in heating single conductors, in which I found that at 

 the temperature of 1000° C. an irregular, arbitrary sort of an 

 electromotive force may be obtained. This is sometimes 



