* 
W. P. Trowbridge—Eficiency of Steam Boilers. 85 
—1°233 
Resuming the expression iba ay ic — if we suppose the 
tube to be extended indefinitely and the gases to be forced 
through the tube by some extraneous pressure, the difference 
between the temperature of the gas within the tube and the 
water would ultimately become zero. 
Integrating the above expression between the limits 4, and 4 
we should obtain an expression by which the relations of ¢ and 
S. and of g and S. become known. t, the difference of tem- 
perature at any point, will be t=O” and g=C” sr 3 
S13 
equations which indicate the form of curve of temperatures 
along the axis of the tube, and also the form of curve of 
emissions of heat along the axis. It is evident that these 
i “and 0” 
element in the problem. It seems evident that, according 
€ present state of knowledge of the conductivity of gases, heat 
must be transferred with excessive slowness, unless currents are 
established in order to bring fresh particles of gas in contact 
with the surface to be heated or cooled each instant. 
y making use of an apparatus like the steam boiler it may 
be possible to determine these constants, as well as the quantity 
t..? for different dimensions of chimneys or force of dra 
thickness of bed of fuel, etc. It would be necessary to make 
the same 
thickness of fuel on the grate, and under the same general con- 
different values of the final temperatures might be obtained 
observed. The quantity of a used being measured, the 
