By Mr. A.E.  Seaton.

My attention was first called to the modern triple compound engine by the published reports of the trial trip of the yacht Isa, and in it I plainly discerned the germs of a successful new type of engine; but it was not until I had seen the engines of the screw steamer Aberdeen erected in the workshops of Messrs. Robert Napier & Sons that I became convinced that it was the engine of the immediate future.  It is, however, due to the farsightedness and enterprise of Mr. C.H.  Wilson, M.P., that I was enabled to try the merits of the new system and compare it with the old.  Mr. Wilson had already viewed the triple compound engine with more than ordinary interest, and it required little persuasion on my part to allow the company to which I have the honor to belong to construct a triple expansion engine in lieu of the ordinary compound for one of four sister ships which it then had in hand for Messrs. Thomas Wilson, Sons & Co., the latter only stipulating that it was to be of the same power as the engine already contracted for.  As I was quite convinced that economy was due to the system rather than to the higher pressure, it was decided not to increase the boiler pressure more than was necessary to suit the triple system.  The other three ships already alluded to were being fitted with engines having cylinders 25 inches and 50 inches diameter by 45 inches stroke, and supplied with steam of 90 lb. pressure from a double ended boiler 13 feet 9 inches diameter by 15 feet long, having a total heating surface of 2,310 feet, so that these engines have every qualification for being economical so far as general proportions go, the stroke being an abnormally long one and the boiler of ample size.  Experience has since shown that these engines are economical in coal, and the wear and tear exceptionally small.

The new engines for the fourth boat were made with considerably shorter stroke, and the cylinders proportioned so as to give equal power; they are 21 inches, 32 inches, and 56 inches diameter by 36 inches stroke, the high pressure cylinder being supported on columns immediately over the medium cylinder, and in other respects these engines were made as near as possible like the other ones above named.  Steam at 110 lb. pressure is supplied from a double ended boiler 12 feet 9 inches diameter and fifteen feet long, having a total heating surface of 2,270 square feet, and identical in design with the boiler supplied for the other engines.  The propellers were made exactly alike in all respects, and the ships being likewise precisely alike, a comparison of the performances of the one fitted with the triple engines could be made with as little grounds for differences of opinion as is possible.  One of the ships fitted with the ordinary compound engines was named the Kovno, that with the triple compound engines the Draco.  Their dimensions are as follows: 

Feet.  Inches. 
Length between perpendiculars.    270    0
Breadth.                           34    0
Depth of hold.                     18    3

And of 1,700 tons gross register.  They are ordinary cargo boats, built of steel, having a raised quarter deck and long bridge amidships, but nothing about them otherwise requires comment.