674 



PROCEEDINGS OP THE AMERICAN ACADEMY. 



electroplated to the nickel. The two from the inside were brought 

 through a fire-clay plug which would completely insulate them. 



2. Source of Heat. 

 The heat is supplied to the interior of the shell by means of an elec- 

 tric heating coil (Figure 3) consisting of German-silver wire. Copper 

 wires were soldered to these, which were taken out of the shell through 

 the fire-clay plug. The oil in the cavity was agitated by two sets of 

 fans soldered to a shaft of steel .7 mm. in diameter. This extended out 

 through the fire-clay plug. A pulley on this shaft was connected by a 

 belt to the small motor M. x . The fans were about 3 cm. in diameter, 

 and so arranged that the oil would circulate towards the centre of the 

 cavity or away, according to the direction of rotation of the fans. 



Figure 3. 



A battery of storage cells supplied the necessary current at a constant 

 pressure. 



3. Constant Temperature Bath. 



For the details of the constant temperature tank see previous article. 



Data. 

 1. Constant Data. 

 The following are the dimensions of the sphere : 



External radius . . . 8.742 cm. ± .00055 cm. 

 Internal radius . . . 3.695 cm. 

 Thickness 5.045 cm. 



2. Experimental Data. 



Procedure. — The general method of procedure in taking a set of 

 readings was to adjust the temperature of the large tank to approxi- 



