In December, 1883, one of the others, the Grodno, sailed from Bombay, and
attained an average speed of 8.5 knots, or 204 miles per day, the engines
making 57 revolutions, with a coal consumption of 12.8 tons per day, or
469 tons on the voyage. The Draco's consumption is therefore 30.5 per
cent. less than that of the Grodno on the round voyage, and 20.3 percent
per day.

The success of the triple compound engine was in these instances more
than had been anticipated, and induced Mr. Wilson to go a step further.
The S.S. Yeddo had been refitted with boilers made for a working pressure
of 90 lb. per square inch, but owing to the size of the shafting the
working pressure was limited to 70 lb.; the average consumption of coal
under these circumstances on two voyages was 17 tons per day. These
boilers had a margin of safety beyond what was required by the rules when
made, and as the Board of Trade rules had been modified in the mean
while, it was found that they could with safety be worked at 100 lb. per
square inch. A third cylinder was now fitted on the top of the original
low pressure, and the safety valves loaded to the 100 lb., and the ship
was dispatched to Cronstadt. After making two voyages under similar
circumstances to the two previous ones, the average consumption was 13.5
tons per day only. In this case it was the same ship, same boilers, same
engines, same propeller, and same men, the only difference being the
addition of a third cylinder and the increase of pressure.

So far all the trials had been made with two crank engines; so it was now
decided to construct another set of engines for 150 lb. pressure, having
a crank to each cylinder. These engines had cylinders 20½ inches, 33
inches, and 58 inches diameter by 36 inches stroke, and were fitted into
the screw steamer Rosario, whose dimensions are 275 feet 3 inches between