175 



It was shown also in the same Paper, that the density of 

 saturated vapour was to be obtained more accurately from 

 this equation, and Eegnault's experiments on the latent heat 

 of a stated weight of vapour, than from any direct experi- 

 ments on the density of vapour made up to that time. This 

 conclusion has been verified by the recent experiments of 

 Messrs. Fairbairn and Tate. With the assistance of some 

 excellent tables in Rankine's " Steam Engine and other 

 Prime Movers," calculated on these principles, the Author 

 has obtained the following results :■ — 



The last column of this table, headed ___ -, is calculated 

 from the column headed __ , by the following formula : t— 



dx 



—dt 



P 



(^+t) 



which shows the height, dx, that must be reached to get a 

 lowering of temperature, — dt, when air saturated with 

 moisture ascends. The pressure, jo, is taken as 2117 lbs. per 



V 



square foot ; and the value of -— , which is the name for the 



t 



