WRIGHT: ELECTRICAL GONIOMETER FURNACE 



397 



sistance furnace to the measurement of the refractive indices of 

 prisms at temperatures up to 750°C. In the different heating 

 devices, however, which have heretofore been employed, in- 

 sufficient attention has been given to the furnace design with 

 reference especially to the heat distribution and to accuracy 

 of the temperature measurements, with the result that the 

 data obtained are encumbered with unnecessarily large prob- 



Fig. 2. Vertical section thru furnace and water jacket; Ai, Ao, water 

 jackets; S, intake for circulating water; F, platinum furnace wires; Ci, C , alun- 

 dum cave on inner faces of which platinum wire spiral is wound; a, alundum seg- 

 ment; B, asbestos ring; /, bare thermal junction; /, crystal; M, magnesium pow- 

 der; D, supporting bar of furnace; Ti, Ti, thermoelement wires. 



able errors. In the present furnace, the effort has been made 

 to meet these objections and to produce an instrimient of fair 

 precision which may serve not only for the measurement of the 

 interfacial angles of a crystal, but also for the direct measurement 

 of its refractive indices at any temperature up to 1150°C., at 



