460 PROCEEDINGS OF THE AMERICAN ACADEMY. 



upon two rings of wood fibre, each 1.5" in diameter, \" thick, and |" 

 wide. These are separated from each other and from the sphere by 

 means of three brass rods y^" in diameter, which are tipped with fibre 

 where they come in contact with the sphere, thus preventing local heat- 

 ing. The two circulating fans, one on each side of the heating coil, are 

 mounted on a shaft of steel which runs in brass bearings mounted on the 

 top of the rings of the heating coil and passing through the sphere in a 

 bearing of wood fibre. 



The shaft terminates just outside the sphere in a piece of fibre 3" long, 

 connected to the driving motor by means of a brass rod. This prevents 

 undue conduction of heat from the interior of the sphere. The leads to 

 the heating coil are rectangular iron wires passing through the sphere in 

 the same plug as the wires to the inside thermo-electric junctions. The 

 current and voltage are measured by an ammeter and voltmeter. 



The sphere thus arranged is suspended in a bath kept at a uniform 

 temperature. The bath is contained in two galvanized iron tanks. The 

 outer tank is 30" in diameter and 30" high, surrounded and covered by a 

 2" layer of hair felt to prevent undue radiation. The inner tank is 15" 

 in diameter and 22" high, supported on the bottom of the larger by three 

 iron supports 3" high. The bottom is perforated with a large number 

 of holes to allow free circulation of the oil. The sphere is supported at 

 the centre of this tank on three wood fibre points, which are held in 

 position by brass rods hung from the top. 



To provide a means for circulating the oil in the bath, two steel shafts 

 are mounted on diametrically opposite sides of the largest tank. Each 

 shaft carries near its centre a fan having four blades 6" in diameter. 



One shaft is connected by a chain to gearing on a shaft in the centre 

 of the small tank. This shaft carries a fan 12" in diameter, which forces 

 the oil up or down the inner tank. On the inside of the inner vessel 

 are three projecting vanes, which break up the otherwise regularly 

 circular motion of the liquid. 



The fans are driven by a motor so arranged that the direction and 

 speed of rotation can be changed. A special distilled petroleum oil was 

 finally selected for the bath. The temperature of the oil is maintained 

 constant by cold water Mowing through a coil of lead pipe surrounding 

 the inner tank. This is connected to a supply tank, thus insuring a 

 constant temperature. It is also connected directly to the water mains 

 and steam pipes, in order to provide a means for rapidly changing the 

 temperature. 



The temperature of the bath can be regulated by hand to give a con- 



