60i 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



1. The couples 1„ 6„ 11,, and 16a, all the guard-ring couples belonging 

 to the cross-section a, were joined in series, and the current sent by 

 this combination through a known resistance was measured. This 

 made it possible to find the difference between the boiling-point of 

 water in the Crafts boilers and the mean temperature of the points a 

 on the guard-rings, and so to find this mean temperature itself 



Similar observations were made with respect to the sections h, c, d, 

 and e of the guard-rings. 



2. The couples a,, a^, (3^, /?„ on the main bars, joined in series, were 

 placed in opposition to the couples 1^, 6a, 11», and 16„ joined in series, 

 and the current sent by this combination through a known resistance 

 was measured. This gave the means of finding the excess of the mean 

 temperature of the points a and e on the main bars above the mean tem- 

 perature of the points a on the inner guard-ring. 



Similar observations gave the means of finding the excess of the 

 mean temperature of the same points a and e on the main bars above 

 the mean temperature of the points e on the inner guard-ring. 



Further observations of a like character gave the excess of the mean 

 temperature of the points b and d on the main bars above the mean tem- 

 perature of the points b and the points d, respectively, on the inner 

 guard-ring. 



The excess of the mean temperature of the points c on the main 

 bars above the mean temperature of the points c on the inner guard- 

 ring was found in like manner. 



3. The spiral couples K K', M M', N N', P P', on the main bars, 

 were joined in series, and the current sent by this combination through 

 a known resistance was measured. This made it possible to find the 

 mean gradient of temperature at the points a and e on the main bars. 



From (1) and (2) above we get the following summary of temperatures 

 and temperature differences : — 



Main bars. 

 Guard -ring, 



Differences, 



Mean a and e 

 Temperature. 



100.28° 5 

 99.56° 



0.72' 



1.52' 



2.00' 



Proceeding with these data, we find by a graphical method that the 

 difference between the mean temperature of the main bars between 



•* The barometer read about 77 cm. corrected, makinj,' the temperature of 

 boiling water about 100.4° at the top of the pot, and perhaps 100.7° at the 

 level of the main bars. 



