CAPACITY FOR HEAT OF METALS AT DIKKKKKNT TKMPERATURES. 



145 



We may hen; point out that the two fundamental observations which determined 

 the temperature range were taken when tin- temperature of the metal was steady and 

 practically uniform, the only ch.-mgr taking place being that due to the very small 

 rate of rise or fall consequent on radiation, &c. 



Fig. 6. "Rise above" for Experiment IV., June 2, 1912 (7 standard cells). 



We have next to consider any other necessary correction for the effect of radiation 

 during an experiment. When the current was established at 9 bridge- wire reading, 

 the oil had first to rise in temperature, then a gradient established from centre to 

 surface of block and, when the temperature began to rise, the thermometer would 

 undoubtedly lag behind the temperature of the surrounding walls. 



For these reasons, the time of rising through the first bridge-wire division would 

 considerably exceed the times of passing over succeeding equal divisions. 



It was found that when the temperature had reached the end of the first bridge- 

 wire division, the conditions had become practically steady, as shown by the fact that 

 in subsidiary experiments in which the current was switched off at the end of the 

 first bridge-wire division, the " rise above " was found to be very nearly the same as 

 when the experiments were completed in the customary manner. 



We also investigated, with the smaller currents, the curve showing the rate of rise 

 of the thermometer throughout this first interval and it appeared that, during the 

 first hah of the time of passing through the interval, the thermometer only rose from 

 9 to 87 bridge-wire. Consequently, this reading 87 bridge-wire may be regarded 

 as approximately the mean temperature throughout the time of the first interval 



VOL. CCXJII. A. U 



