Nitrogen Thermometer rom Zinc to Palladium. 113 



during the observations. The arrangement made for the pur- 

 pose is very simple and effective, as can be seen from the 

 neighboring diagrams (figs. 4 and 5). The last two series of 

 measurements were made with this appliance^ and the fixed 

 distance was found to remain constant throughout the series 

 to within 0*003 mm , although on first setting up the apparatus a 

 gradual adjustment of strain, amounting to 0'012 mm , took 

 place during the first two days. 



The determination of j3 is subject to two errors ; the first 

 is uncertainty of temperature, the second occurs in the measure- 



FlG. 5; 



Fig. 5. A section through the furnace at one of the openings, showing 

 the method of illumination of the heated bar and the standard cold bar (I) 

 together with an arrangement for checking the distance apart of the cross 

 hairs at each temperature. With a screen inserted at a only the hot bar is 

 visible ; with the screen at b only the cold bar. 



ment of the change in length. It was impossible to wind the 

 furnace (70 cm long and 2 cm inside diameter, with two side open- 

 ings) so as to give a perfectly uniform temperature along the 

 bar ; but as the furnace winding and consequent distribution 

 of temperature were varied considerably for each run, the 

 uncertainty from this cause was eliminated in the average of 

 all the observations. The error in the temperature measure- 

 ment itself was probably not over 2°, which would give an 

 error of less than 0*2 per cent at the highest temperature. 

 Two thermoelements with a common junction were used, one 

 entering from each end of the furnace. This not only gave 

 a second temperature reading in confirmation of the first, but 



