FRICTIONAL LOSSES IN INTERNAL COMBUSTION ENGINES. 509 
Having found the moment of inertia of the rotating 
masses by combined free and braked retardation tests, the 
torque producing retardation in the main tests, i.e., the 
friction torque, was straight away calculated and also the 
friction loss at the given speeds. | 
The friction loss in Section (a) is the total loss in the 
whole engine and corresponds to the ordinary no-load losses. 
of an engine, except for the special conditions stated in §7. 
Deducting from this the friction loss in Section (c) gave 
the loss due to the friction of the piston, both ends of the 
connecting rod and the gas friction through the ports, etc. 
These were separated by further tests, § 10. 
On subtracting the results of (d) from (c) the friction 
loss of the valve gear becomes separated. Finally, the runs 
made under conditions (d) gave the main bearing friction 
directly. ; 
10. Measurement of Gas Friction.—In order to isolate 
the friction losses due to piston, connecting rod and gas 
passage, some auxiliary experiments had to be performed,, 
Since the retardation method could not satisfactorily be 
used. 
The best way to measure the power lost in forcing the 
gas through the valves and passages seemed to be by taking 
indicator cards. Accordingly cards were taken with the 
engine running under full compression, but not under power; 
1.€., under exactly the same conditions as governed the 
retardation tests. The algebraic sum of the areas on the 
card enveloped during four strokes, or a complete cycle,. 
will represent the net negative work. Such cards were 
taken at a range of speeds and the corresponding torque in 
each case was found. A curve was then drawn showing 
the variation of this equivalent torque with speed. By 
this means the results of the test were made comparable 
