177 



eight centimeters apart on all sides except in front of the glass door. Ti 

 was a copper vessel or tank connected by lead tubes La and L, to the tank 

 T2. Both tanks were filled with oil. The oil in the tank Ti, heated by one 

 or more bunsen burners, passed through the tube L, into the tank Tj and 

 finally back through Li into Ti. A stirrer, driven by an electric motor, 

 aided in producing a rapid circulation of the oil. Tank Ti and tubes La 

 and L2 were wrapped with several layers of asbestos paper. 



From a flask not shown in the figure water was siphoned to and 

 through the tube Gi into the evaporating dish Di. An overflow G2 served 

 to keep constant the depth of the water in the dish. The excess of water 

 dropped on sponges S in an evaporating dish D3, itself drained by the tube 

 T3. The sponges served to keep the space inside the box saturated with 

 watery vapor, or nearly so. An inverted evaporating dish Do served to 

 enclose almost completely the frame and liquid and thus Insure the satura- 

 tion of the space about the film on which the measurements were made. 



The dish Di rested on a wooden platform P supported at one end by 

 a hinge and at the other end by a cord C passing over a cylindrical metal 

 rod which extended to the outside of the box. The height of the water 

 surface was slowly raised or lowered by twisting the rod. 



A thermometer ti gave the temperature of the oil, t, the temperature 

 of the water, tg the temperature of the space immediately above the water, 

 and ti the temperature of the space outside the inverted evaporating dish. 

 No measurements were made when the thermometers t,, U, and ti differed 

 by more than a few tenths of a degree. This necessitated a wait of from 

 one to five hours between readings at different temperatures. Three series 

 of readings were taken, each requiring a continuous run of from ten to 

 thirty-six hours — depending upon the number of observations made. 



Owing to the condensation on the wire W where it passed through the 

 opening in the tank T, it was not practicable to carry the observations 

 higher than 80°. An effort was made to prevent tiiis condensation by driv- 

 ing gently through the opening a stream of warm air from the outside. 

 But this interfered somewhat with the action of the balance and the satu- 

 ration of the space inside. It did not occur to the writer at the time to 

 try heating the wire by means of an electric coil. 



For temperatures below room temperatures the asbestos was removed 

 from the tank Ti and the tank was surrounded by a large vessel containing 



[12—26988] 



