408 
PROFESSOR O. REYNOLDS AND MR 4Y. H. MOORBY 
it was determined under conditions which ajrproximated closely to those which held 
in the main trials, it was used in the calculation of the correction given below. 
The weight of water vapour at a temperature of 212° per cubic foot = 0-03797 lb. 
Therefore the correction due to the loss of the latent heat necessary to evaporate 
this weight of water, is, relatively to the 180 thermal units generated per lb. of water 
discharged by the brake, 
4 _ 2-2 _ 0-03797 x 966 
5 ^ 1728 ^ 180 
0 - 00021 . 
The correction factor is therefore (1 — 0-00021). 
IV.—Reduction of the Weighings to Vacuo. —(Part 1, par. 41.) 
60. Taking the density of water 
and of air at 32° Fahr. 
= 62-425, 
== 0-08073, 
and also assuming 70° Fahr. as the mean temperature of the engine-room during the 
trials, the correction factor becomes 
49-1 1 
1 - 0-08073 X X 
1 — 0 - 00120 . 
In the calculation of this factor it must be borne in mind that the density of the 
air causes errors of equal magnitude in the measurement of both work and heat on 
account of the alteration of apparent density of the cast-iron weights used on the 
brake and on the lever of the weighing machine. 
V .— Varying Specific Heat of the Water. —(Part 1, par. 51.) 
61. According to PtEGNAiiLT the mean sjjecific heat of water between freezing and 
boiling points is 1-005, assuming the specific heat unity at the lower temperature. 
If his formula for the specific heat be correct, then a correction factor of (1 — 0-00006) 
is necessary to make the value of K derived from the trials represent this mean 
specific heat. This factor is introduced because it was not strictly the whole range 
of temperature between freezing and boiling points which was dealt with in the 
trials, lor the cold water supplied to the brake had various temperatui'es ranging 
trom 32 - 7 ° to 34 - 3 °. This correction would only just aft'ect the second decimal place, 
and m consideration of the uncertainty that exists as to the exact value of the 
specific heat of water at any temperature, I do not propose to use a correction factor 
on this account. 
