Nitrogen Thermometer from Zinc to Palladium. 105 



tion around the circumference of the bulb. This amounted 

 in the worst case (at 1450°) to a variation of 1*3° from the 

 mean, four elements being used around the circumference to 

 make the test. This variation seemed to be due either to 

 unequal conductivity of the furnace material at different 

 points or to the falling off of small portions of the furnace 

 lining, leaving exposed places on the wire. Variations of 

 this character are probably an unavoidable result of using a 

 furnace where the heat supply is so near to the point where it 



Fig. 2. 



Fig. 3. 



Fig. 2. Section of furnace and bulbshovving the arrangement of coils and 

 diafranis about the bulb which gave the most uniform temperature distri- 

 bution in the measurement of both high and low temperatures. The sup- 

 plementary end coils were independently heated and regulated. 



Fig. 3. A special arrangement of the heating coil and diaframs designed 

 to give a very uniform temperature distribution about the bulb. The coil 

 was heavily ballasted inward with a good heat conductor and outward with 

 a poor conductor. The heating coil was also divided into three sections 

 which could be independently regulated. This furnace was used at the 

 copper point only. 



is measured, as is the case with the furnace which is wound 

 on the inside. This form of winding is necessary, however, 

 in order to reach the highest temperatures, so that absolute 

 uniformity of temperature around the bulb had to be sacrificed 

 to increased range of the instrument. 



After this variation was discovered, measurements were 

 always made with four elements at eoual distances around the 



