( 28 ; 



On an Equation between the Temperature and the Maximum 

 Elasticity of Steam and other Vapours. By William 

 John Macquorn Rankine, Civil Engineer. (With a 

 Plate.) Communicated by the Author. 



In the course of a series of investigations founded on a 

 peculiar hypothesis respecting the molecular constitution of 

 matter, I have obtained, among other results, an equation 

 giving a very close approximation to the maximum elasticity 

 of vapour in contact with its liquid at all temperatures that 

 ixsually occur. 



As this equation is easy and expeditious in calculation, 

 gives accurate numerical results, and is likely to be practi- 

 cally useful, 1 proceed at once to make it known, without 

 waiting until I have reduced the theoretical researches, of 

 which it is a consequence, to a form fit for publication. 



The equation is as follows : — 



(1-) 



Whei'e P represents the maximum pressure of a vapour 

 in contact with its liquid : — 



t, the temperature, measured on the air-thermometer, from 

 a point which may be called the absolute zero, and which 

 is — 



274'^'6 of the centigrade scale below the freezing point of 



water. 

 462'''28 of Fahrenheit' s scale below the ordinary zero of 

 that scale, supposing the boiling point to have been 

 adjusted under a pressure of 29-922 inches of mer- 

 cury, so that 180° of Fahrenheit may be exactly equal 

 to 100 centigrade degrees. 

 461°"93 below the ordinary zero of Fahrenheit's scale, 

 when the boiling point has been adjusted under a pres- 

 sure of ;;0 inches of mercury, 180° of Fahrenheit being 

 then equal to 100°-0735 of the centigrade scale. 



