could be calculated with any degree of accuracy. On trial trips with the
steamers already named, the consumption of ordinary South Yorkshire coal
was 1.6 lb. per indicated horse power, and the consumption of water per
indicated horse power calculated from the high pressure indicator
diagrams was 1.41 in the Draco, 13.2 in the Rosario, and 13.16 with the
Finland, or taking the medium pressure diagrams, it was 12.2, 1.30, and
11.95 respectively. Twelve months ago we constructed for Messrs. Thomas
Wilson, Sons & Co., two sets of triple expansion engines of 600 indicated
horse power, one having two cranks and the other three cranks, the
engines, boilers, and propellers being otherwise exactly alike and fitted
into sister ships. The water consumed in the three crank engine is 12.93
lb., against 13.0 in the two crank, but the former drives its ship nearly
½ knot per hour faster than the latter does its, and when both ships are
driven at the same speed the consumption of coal in the three crank ship
is considerably less than in the other.

We have now entirely given up the construction of two-crank triple
expansion engines, because of the impossibility of equally dividing the
work between the cranks; for, although the engine when running appeared
to be perfectly balanced, the wear of the brasses of the crank having the
two cylinders was always considerably more than that of the other.
Placing the high pressure cylinder over the low pressure cylinder seemed
to give the most satisfactory results, but even these were far inferior
to those once obtained with the three cranks. We have lately constructed
some very small three-crank engines from which exceedingly good results
were obtained; the cylinders are only 11½ inches, 17 inches, and 30
inches by 18 inches stroke, which developed 218 indicated horse power
with a consumption of 12.8 lb. of water per indicated horse power, and
this, together with some other observations, leads me to believe that the
best economical results will be obtained by running triple expansion