Manchester Memoirs, Vol. xli. (1896), No. 3. 9 



to the temperature of saturated steam at pressure P 2 \ 

 And if, further, H x equals the equivalent of the total heat 

 of evaporation at pressure P/ per lb., then 



HZ-SrfH-to+Ai (2). 



And if, similarly, H 2 and h 2 correspond to the temperature 

 of saturated steam at pressure P 2 ', then 



H 2 ' = S 2 (H 2 -h 2 )+h 2 +K(T 2 '-T 2 ) (3). 



Where K is the mean specific heat of steam at constant 

 pressure between the temperatures T 2 ' the actual tem- 

 perature at B, and T 2 the temperature of saturated steam 

 at the actual pressure (P 2 ') at B. It being noticed that, it 

 1 — S 2 is greater than nothing, T 2 '=T 2 , so that the last term 

 in (3) vanishes. While, if (1 — S 2 ) is zero, this last term ex- 

 presses the heat, whatever it may be, requisite to raise 

 steam, at constant pressure P/, from the temperature ot 

 saturation T 2 to the observed temperature T 2 '. 



Substituting from equations (2) and (3) in equation 

 (1), this becomes 



SifHx-AO+Ai+^+H, 



=S 2 (H 2 -h 2 )+h 2 +f g +K(T 2 '-T 2 ) (4). 



If then u l9 u 2 , and H ; are small enough to be neglected, 

 since the values of H 1? h u H 2 , h 2 , T 2 are obtainable from 

 Regnault's tables, when P/, P 2 ' or T/ are observed, all the 

 remaining quantities may be known except Si, S 2 , and K. 

 And either, if S 2 is not equal to unity, (T/— T 2 )=o, and 



Sx (H 1 -h 1 )+h 1 =S 2 (H 2 -h 2 )+h 2 (5), 



or, if (1 — S 2 )=o 



Si (H 1 -/ h )+/z 1 =H 2 -f-K (T 2 '-T 2 ) (6). 



Equation (5) gives S x in terms of S 2 when T 2 '=:T 2 , but, 

 since S 2 is unknown, this is of no use; while, if T 2 ' is greater 



