706 Report of the Consulting Engineers on the Trials of 
point C, draw a tangent to the curve cutting the base at the 
point B, which proves to be 7 h. 21 min. distance from A. It 
is clear that if the rate of cooling were uniform, as represented 
bj the tangent C B, the 321,105 units of heat at 0 would 
be dissipated in 7 h. 21 min. (or 7 35 hours), instead of 12^ 
hours, as was actually the case, but at c the tangent coincides 
with the curve, so at that point of it the rate of cooling was 
43,688 units per hour. 
In this manner the greater number of the engines were tried, 
and the results of the computations are given in Table IX., 
page 729. 
To make the loss by cooling more evident, we have (in 
line 10) compared it with the number of heat-units latent in the 
coal consumed per hour, and the loss appears to range from 3J 
per cent, to 16^ per cent. In line 11, the number of units dis- 
sipated per brake horse-power has been calculated and set 
down. 
It will be noticed that Davey Paxman's Compound Engine, 
3124, even after allowing for the increased temperature at which 
it worked, cooled about 27^ per cent, more rapidly than their 
simple engine, 3125. The two engines were lagged in precisely 
the same manner. The compound had rather more surfaces in its 
machinery, but hardly enough to make the difference observed. 
Mr. Paxman suggests that the ash-pan damper of the compound 
engine might not have closed perfectly, and that thus a current 
of cold air was allowed to pass through the boiler. 
It will be seen from the results obtained that much economy 
may be expected from careful and efficient lagging of all the 
hot parts of engines. This table also serves to explain, to 
some extent, why Mr. Foden did not do better with his higher 
pressures, and shows generally that, besides other reasons already 
given, the increased loss by cooling at higher pressures tends to 
set a limit to the economy to be derived from extending them 
beyond comparatively narrow limits. 
The foregoing calculations, the observations made during the 
" Trials," and Mr. Stead's analyses, furnish the means of insti- 
tuting a comparison between the quantity of heat g^enerated 
by the combustion of the fuel and the amount utilized or 
dissipated wastefully ; we can in fact compile a balance-sheet, 
on the debtor side of which will appear all the heat developed 
in the furnace, and on the creditor side an account of the 
various ways in which it was appropriated. 
From the analysis of the wood used in rekindling the fires, 
after the preliminary runs, which will be found at the foot of 
page 707, and from that of the coal given in Table VIL, page 727, 
it will be seen that carbon and hydrogen are the two elements, 
