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 1/2 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 111/2 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 engines at a much higher number of revolutions than is usual, and with a rate of expansion not less than 12 for a steam pressure not less than 140 lb. (155 absolute).  The largest engines we have made of this type so far are those of S.S.  Martello, which have cylinders 31 inches, 50 inches, and 82 inches diameter by 57 inches strokes and indicate at sea 2,400 horse power when running at 60 revolutions with steam of 150 lb. pressure; the consumption of Yorkshire coal is 37 tons per day average throughout a New York voyage.  Had Welsh coal been used in every case, the results would have been very much better, for, in addition to the superior evaporative power of Welsh coal, it is slow burning and much more easily controlled, especially on the comparatively short grates of these modern boilers, the quick-burning Yorkshire coal causing the safety valves to frequently blow off when working near the load pressure unless great care is taken by the firemen.

I trust these few particulars may be of interest to the Institution, and especially to those members of it who are particularly interested in the commercial success of our mercantile navy.  I have purposely avoided engineering details and technicalities of any kind, giving only such information as will tend to give British shipowners faith in that form of engine which will undoubtedly help them to successfully tide over bad times, and keep the bulk of the carrying trade of the world in their hands.

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EARLY HISTORY OF THE STEAM JACK.