THEORY OF THE STEAM ENGINE. CXXXV. 
stated by De Pambour, the friction of an engine consists of two 
parts—its friction when running unloaded, and in addition, a 
further amount caused by the engine taking up its load, and so 
increasing the pressure on the running parts. This is undoubtedly 
correct, but practically it is often found, more especially in the 
case of non-condensing engines, that this additional frictional loss 
is not important or even observable. The frictional waste is 
generally only a small percentage of the total waste in an engine, 
and as its amount can be very approximately determined, the 
total error introduced into the designer’s computations is unimpor- 
tant and calls for no further treatment. 
©. There thus remains only the thermal loss to deal with, and 
this most important form of waste due to conduction and radiation 
of heat within and from the cylinder, is the point towards which 
nearly all recent investigations have been directed. One portion 
of the radiation loss is external and takes place through the heated 
cylinder heads and barrel (to an extent dependent on the quality 
of the lagging) and also from the piston and valve rods alternately 
heated and cooled as they enter and leave the cylinder. This 
Portion of the loss is small in amount (as may be seen from the 
foregoing table) and regular in action, and consequently in any 
given case may be readily computed from observations taken under 
Similar conditions in actual practice. The second and by far the 
most important portion of this waste due to conduction and radi- 
ation is internal, and constitutes the much discussed “ cylinder 
condensation.” Its importance is due to the fact that it is large 
in amount and that the causes affecting it are not thoroughly 
understood, no formula or principle either empirical or rational 
having yet been produced which satisfactorily expresses it. 
The general reason for the occurrence of cylinder condensa 
is to be found in the fact that the cylinder is not made of non- 
conducting material, and that the interior walls of the cylinder 
are not at the same temperature as the steam in contact with them. 
tion 
1“ On the distribution of internal friction of engines,”—Trans. Am. 
Soc. Eng., Vol. x. 
