336 Prof. J. D. Everett on the Comparison of 



straight line making intercepts t, t' on the axes is represented 

 by equation (2) and will pass through the fixed point x= —k/c, 

 y=\jc. In practice k is positive; hence one of the two 

 coordinates of the fixed point is positive and the other 

 negative. As c is small, the point is at a considerable 

 distance. 



Ramsay and Young's law is thus equivalent to the fol- 

 lowing statement (see fig. 1) : — If the absolute temperatures 



at ivhich two vapours have equal pressures are represented by 

 lengths X, Y laid off along two lines inclined at any angle, 

 the line X Y joining their extremities willy when produced, pass 

 through a fixed point P lying at a considerable distance. Two 

 pairs of corresponding temperatures (preferably far apart) 

 are theoretically sufficient to determine the position of P; 

 and then the temperature of one substance corresponding to 

 a given temperature of the other is found by merely drawing 

 a line through two given points. 



It is not necessary to use the same scale for t ! as for t ; for 

 equation (2) may be written 



* . %_i 



t + 2? ' 



showing that the effect of doubling the scale for t' is simply 

 to double the ordinate y of the fixed point. A table given 



