HALL. — CONDUCTIVITY OF MILD STEEL. 291 



The following observations accompanied those just recorded : — 



t = temperature of water running from lower chamber. 

 tx = " " at thermometer T'j, Fig. 1. 



>S' = number of seconds required to fill flask F\ Fig. 5. 



^ -— 44 4« " U p U 



The capacity of each flask was about 1800 grams. The numbers in 

 brackets in the column headed S^ indicate the number of grams of 

 water escaping per minute through the overflow tubes of the lower 

 chamber. In the column aS is a similar note for the upper chamber. 



Means 21°.9 32°.5 31°.7 70.8 72.9 



The 50 grams per minute noted as the overflow from tlie upper 

 chamber is disregarded, not because it is inconsiderable in comparison 

 with the main stream, which carried about 1400 grams per minute, 

 but because it was taken off without having been brought near the 

 disk, so that its temperature must have been practically unaffected by 

 its admission to the chamber. 



Assuming, for our present purpose, that no corrections need be 

 applied to the thermometer readings, we see that the water escaping 

 from the jacket is about 0°.8 colder than it was when it entered the 

 upper chamber, that the difference of temperature of the streams in 

 the two chambers is about 10°, and that the temperature of the disk 

 must be about half way between those of the streams, 27°, let us say. 

 The main object in noting the difference between ^j and U is to get 

 information as to the effectiveness of the jacket that surrounds the 

 upper chamber. If, as in this case, the temperature of the jacket 

 differs only 1°, or thereabout, from the temperature of the chamber, 

 the protection afforded must be nearly perfect. Apparently the differ- 

 ence was little, if any, more than 1° in any case. 



