398 Mr. W. B. Burnie on the Thermo-electric 



cracking due to the freezing of the metal, and allowed to 

 cool. The superfluous metal was then melted out of the open 

 limbs. The two copper-metal junctions were to be in the 

 two open limbs of the tube, and a number of thick copper 

 wires were so arranged round the outside of the tube as to 

 conduct away the heat from all parts not in the immediate 

 neighbourhood of the hot junction. By this means all the 

 metal except a small portion was kept solid, and the level of 

 the melted metal was always higher in the open than in the 

 closed limb. This was necessary, as the solid metal was not 

 a satisfactory cork for the tube, and a slight liquid pressure 

 was needed to keep good contact between the liquid and 

 solid metal. 



The temperature-differences between the hot and cold 

 junctions were measured with a thermo-element of platinum 

 and a platinum-rhodium alloy (Pt 90 per cent., Rd 10 per 

 cent.). This thermo-element was calibrated between the 

 temperatures of 0° C. and 263°'5 C. by comparison, in linseed 

 oil, with a Reichsanstalt standardized thermometer. The 

 calibration curve was then extrapolated as far as 430° C. by 

 means of an equation. For reasons which will be explained 

 later, it was useless to adopt any more accurate method than 

 this for the first set of experiments. The thermo-element was 

 insulated within and from without with asbestos paper, and 

 each junction was bound to one of the standard copper wires. 

 These copper wires were also insulated with asbestos, so that 

 only their ends, which were in close proximity to the junc- 

 tion of the temperature-measuring thermo-element, were 

 uncovered. 



Some experiments were made to determine the electrical 

 insulating properties of asbestos paper at high temperatures, 

 and it was found that the errors introduced by the electrical 

 conductivity of the supposed insulator were, up to 600° C, 

 negligibly small. Other experiments were made to deter- 

 mine whether or not the temperature of the junction in 

 asbestos differed greatly from the temperature of the metal 

 surrounding the asbestos. One junction of the temperature- 

 determining thermo-element was immersed in melted lead, 

 and the other in melting ice. The parts of the wires just 

 outside the lead were alternately heated with a burner, 

 w hereby the temperature-difference between the junction and 

 the metal would be decreased, and cooled with an air blast, 

 whereby the temperature-difference would be increased. 

 Readings of the temperature-difference between the two 

 junctions were meanwhile taken ; and it was found that by 

 varying the temperature of the leading-in wires the tempera- 



