222 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



immersing this in ice as in Figure 3, except that the latter makes a 

 rather more bulky mass to insert in the ice. 



The wires were also fused together at the hot junction except when 

 this was unnecessary on account of their being immersed in metal. 

 It may be noted here that, as a null method was employed, the total 

 resistance of the thermal circuit, or any variation in it, was without 

 effect other than a corresponding change in sensitiveness. 



As the hot junction was to be immersed in vapor of sulphur as one 

 of the known temperatures, the following apparatus was designed for 

 this purpose. It is substantially the sulphur boiling point apparatus 



Fig. 3. 



of Griffiths, and is shown in Figure 4. A glass tube, A, similar to the 

 Victor Meyer vapor density tube, 16 inches long and with a two-inch 

 bulb, was provided with an asbestos jacket and hood, B. B. The 

 upper few inches of the tube were wound with a spiral wire spring, S, 

 which rendered this part efficient as a condenser. The top was closed 

 with a layer of asbestos. Two overlapping diaphragms of asbestos 

 were inserted in the tube at D and E. The couple passed downward 

 throuo-h a glass tube to the asbestos tubular hood, (7, which served as 

 an umbrella to shed the dripping cooler sulphur, and as a radiation 

 screen. The hood, however, had openings top and bottom for the 

 free circulation of the vapor. An asbestos diaphragm, H^ upon which 

 the bulb rested, reduced the chances of superheating. 



