426 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



of temperature. To prevent this drift, and to prevent, as far as possible, 

 tiie flow of heat from the thermostat into the room, water-windows 

 were placed just inside of the air-bath and opposite the small openings 

 in the cylindrical shell. 



Figure S shows a cross section of the thermostat, made through the 

 water- windows, the telescope, and the source of illumination. L M N 

 is the air-bath ; E and F are the halves of the cylindrical asbestos 

 shell ; A and B, the two water- window s. The openings at K and J 

 and those at H and I, were closed by plate-glass windows. 





FlGCRK 4. 



Dilatometer and Piezometer. 



The 'dilatometer (Figure 4) consisted of a C3dindrical glass bulb HG, 

 30 cm. long and 1.7 cm. in diameter. For purposes of filling, which 

 operation will be described later, one end of this bulb was closed by 

 means of the stopcock K. At right angles to the axis of the bulb and 

 midway between its ends was sealed another glass tube 5 cm. long, and 

 of the same internal diameter as the bulb. The lower end of this 

 short tube was closed, and to it was sealed the capillary tube ABCD, 

 which from A to B was parallel to the bulb, from B to C at right angles 



Figure 6. 



to it, and from C to D again parallel to it. Near the end D this tube 

 carried the rubber stopper M. The purpose of this stopper will be 

 explained later. Inside the bulb of the dilatometer there was a spiral 

 of fine platinum wire, to be used as a platinum thermometer. The de- 

 scription of the use of this platinum thermometer will be postponed. 



The piezometer (Figure 5) consisted of the cylindrical bulb N, to one 

 end of which was sealed the capillary tube P. The piezometer also 

 contained a platinum thermometer, the lead wires of which passed out 

 through the rubber stopper L. The capacity of the piezometer was 

 determined by weighing it empty and then weighing it filled with 



