412 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



the required percentage correction curve by translating piston displace- 

 ments into volumes and dividing by the volume of the kerosene in the 

 lower cylinder at the corresponding pressure as already determined. 

 The correction curve actually used is shown in Figure 18. It is ob- 



-20 



-10' 10^ 



TEMPERATURE. 



ZQ" 



Figure 18. The corrections duo to the thermal dilatation of the trans- 

 mitting liquid and the elastic deformation of the cyUnder to be applied to the 

 directly measured change of liquid mercury when it passes to the solid state. 



tained by combining with this temperature correction the correction 

 already determined for the elastic deformation of the upper cylinder. 



The correction curve so detennined is not linear, the values being 

 2.0 per cent at —20°, 0.6') per cent at 0°, and at +20°. The depar- 

 ture from linearity is evidently due to the decreasing dilatation of the 

 kerosene under high pressures. 



Temperature Correction for the Upper Cylinder. — In the form of appa- 

 ratus used in this experiment there is one other small correction because 

 the upper cylinder is exposed to the slightly varying room temperature. 

 If the room temperature changes during freezing, the observed change 



