The Trials of Light Portable Motors at Plymouth. 591 
per stroke, reckoned as steam at the pressure o e, and draw 
another saturation curve h Jc. Then any abscissa, such as 
a d, represents the steam which ought to be found in the cylin- 
der at the period of expansion when the pressure was oa. 
But the diagram shows that there was only present as steam at 
that time the volume a c. Hence c d represents steam condensed 
by the action of the cylinder sides. With a slight reservation, 
which need net be insisted on here, the horizontal intercept 
Fig. 2. 
o \ j 
between g I and h Jc represents, for each point of the expansion, 
the amount of condensed steam in the cylinder. The approach 
of g I to h Jc would mean that there was re-evaporation due to 
heat abstracted from the cylinder wall. The ratio a c-^-ad is what 
is termed the dryness fraction of the steam, and this has been 
calculated, and marked on the diagrams, at cut off and release. 
Taking Messrs. Adams's diagram first (fig. 3), it is seen that 
the dryness fraction at cut off is 0'602, so that four-tenths of the 
steam in the cylinder has been condensed at cut off. At release 
the steam is a very little drier. The steam is wiredrawn during 
admission, the cylinder being somewhat too large for the work 
to be done. As this engine is regulated by a governor acting on 
a throttle valve, there would have been on the average the same 
wiredrawing if the governor had been in action, but the diagrams 
would have varied more. The diagram is a fairly good diagram 
for an engine working at the pressure and speed selected by the 
exhibitor. The real ratio of expansion in this engine was 1*6. 
The diagram of the engine of Messrs. E. R. & F.Turner (fig. 4) 
shows very strikingly the defects inherent in small, slow-running 
Bingle cylinder engines. The condensation in the cylinder is 
enormous. The dryness fraction at cut off is 0-487, so that more 
