330 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



Dilatation at Low Pressures. 



For the thermal dilatation at low pressures, two sets of determina- 

 tions were made; one was the series of isotherms at four different 

 temperatures already mentioned, and the second was by the method 

 adopted for the higher pressures, namely variation of temperature 

 at constant mean pressure. The method of calculation for this lower 



23456789 10 U12 

 Pressure, kgm. / cm.^ x 10^ 



Figure 2. The change of volume of water for intervals of 20° plotted 

 against pressure. 



range was not the same as that employed for the higher pressures, 

 as already explained, due to the fact that the slope of the isothermals 

 is not sufficiently independent of temperature at the lower pressures. 

 The method of computation adopted here was a graphical one, by 

 plotting the observed volume and pressure points for the different 

 temperatures and taking the difference between adjacent curves 

 graphically. The temperatures at which the different determina- 



