Trials of Portable Steam- Engines at Cardiff. 53 
At Wolverhampton, the Society gave up the task altogether, 
and left each Exhibitor to do that which was right in his own 
eyes ; the result was, that the circular inches varied from 10^^ to 
^TcT P^^ horse-power. 
Tliis year, however, the Society thought it right once more to 
lay down a rule. It was as follows, Condition II. : — • 
"The nominal jiowcr of the engines entered for trial will be taken at \ the 
iadicated jwwer, at GO lbs. pressure in the boiler, cutting off" at -J the stroke, 
and the peri]iliery of the fly-wheel running 1884 feet per minute." 
This rule is clearly based on the speed of strap usual for 
driving threshing-machines, and it will be seen was intended to 
limit the purchaser's views to just about, or a little below, the 
true Jack Cade standard, viz., to a demand of about three times 
the nominal power, and it is said to have had the result of satis- 
fying everybody interested. This being so, it would be im- 
proper for the Judges to make any comment upon it. They 
will therefore only say that they do not understand how a rule, 
which, while specifying fly-wheel rim speed, ignores the length 
of stroke and the diameter of fly-wheel, can by any possibility be 
practically applied, unless there be an uniformity of proportion 
among the makes of portable agricultural engines as regards 
these two points. In effect, this seems to be nearly so, and thus, 
the speed of the fly-wheel rim is an exponent of the speed 
of the piston. Were it not, this curious event would happen, that 
if a maker sent two engines to be tried, exactly alike in all 
respects except in the diameters of the fly-wheels, the engine 
which had the smaller fly-wheel would be estimated as being 
of proportionately greater power than the engine which had 
the larger wheel : so that a maker, by halving the diameter of 
his fly-wheel, could double the nominal power of his engine, 
because to attain the same rim-speed, he must make double the 
number of revolutions that he would have to make if he used 
the larger wheel, and thus the calculated indicated power would 
be doubled. It is true that the boiler would not, in all proba- 
bility, supply the steam for the double speed, but then, Condi- 
tion II, does not say that it shall, but merely provides a basis of 
calculation for the power of the engine, on the assumption that 
the steam is there. 
It is much more easy, however, to criticize than to suggest 
a remedy. One of the writers of this Report has the 
honour to be a Member of Council of two engineering societies, 
to which the Board of Trade, some months since, addressed 
letters, asking their advice as to what could be done to define 
a commercial horse-power. One of these societies is the Institu- 
tion of Naval Architects, and, as their action in the matter is 
over, the writer is at liberty to state what took place. 
