434 PROCEEDINGS OF TIIE AMERICAN ACADEMY. 



to be unreliable, however, apparently due to inconstancy in the amyl- 

 acetate standard. 9 The furnace was therefore calibrated by means of a 

 platinum platinum-rhodium junction, that is, the temperature of the 

 crucible was measured while the power was held constant The tern- 



perature was then subsequently determined by measuring the power 

 applied. Heating was furnished by an alternating current with a fre- 

 quency of sixty cycles per second. This was taken from a transformer- 

 switchboard so arranged that the voltage could be varied in steps of 

 about twelve volts. For the finer regulation a carbon plate rheostat, in 

 which current regulation could be obtained by varying the compres- 



9 The temperatures measured in the former article on this subject arc ac- 

 cordingly from 100° to 150° too low, but the general conclusions there reached 



are not affected. 



