A. L. Day and J. K. Clement — Gas Thermometer. 429 



giving an intense and concentrated illumination. It was 

 mounted behind the furnace some 20 cm distant from the open- 

 ings, and was so screened that its heat did not reach the 



Fig. 6. 



Fig. 6. The expansion apparatus. A photograph of a furnace and acces- 

 sory apparatus for the determination of expansion coefficients over long 

 ranges of temperature. The illustration represents a later form of appara- 

 tus than that described in the text. The difference lies mainly in the 

 increased length : the present furnace is arranged to take bars 50 cm long 

 instead of 25 cm as described. 



optical parts of the apparatus save in the two beams which 

 enter the furnace for the illumination of the bar. 



The temperature of the bar was determined at first with 

 one thermoelement and afterward with two, which entered the 

 furnace tube from opposite ends in such a way that their hot 



