504 E. P. TAYLOR. 
from that of the atmosphere to figures above ordinary 
running temperatures. From these tests the total friction 
torque and friction horse-power were found at several 
speeds. Next, the big end of the connecting rod was dis- 
connected so that a retardation test now would give a 
friction-power loss less than before by an amount equal to 
the power lost in friction of the piston, of both ends of the 
connecting rod and of the gas through ports. The flywheel, 
shaft and valve gear have in this case, of course, to be run 
up to speed by external means. Finally, the lay shaft was 
taken off so that now there remained only the main shaft 
in its bearings to cause any friction. The friction loss in 
this part of the engine was, therefore, got directly from 
the retardation test run when in this condition. 
7. Conditions of the Tests.—It is convenient at this 
stage to call attention to what these friction losses actually 
represent, and to the conditions under which the results 
were obtained. All the tests were made under circum- 
stances as nearly as possible representing usual running 
practice. This could be easily arranged as to temperature, 
lubrication and speed, but the circumstance of load on the 
rubbing surfaces could not be represented in the tests. 
For instance, in the fully-assembled tests there neces- 
sarily could not be explosion pressure on the piston, with 
consequent increase in the piston thrust on the cylinder 
walls, and in the shaft and connecting-rod pressures. On 
this account the fully-assembled engine-friction-horse- 
power loss from a retardation test may not be the same as 
the no-load indicated horse-power as ordinarily obtained. 
Again, after disconnecting the big end of the connecting 
rod the friction in the main-shaft bearings is no longer 
influenced by any pressure on the piston that would other- 
wise have been communicated to the shaft. Therefore, 
one cannet say that the friction measured at the main 
bearing is all that is generated there when fully assembled. 
