and the power of the engine is diminished nearly one-half."
Many pages are taken up by an exhaustive description of the slide valves and the singularly intricate valve gear by which these remarkable results are achieved, the writer's enthusiasm leading him finally to proclaim that "the great perfection of the present locomotives, and their superiority to the old ones, is caused not so much by the application of new inventions to them as by the combination of many former ones, and the uniting together several plans which, separately, would be but of small value."
With these evidences of superiority before us it is saddening to reflect upon the probable condition of affairs prevailing in the cylinders of "the old ones."
But we must hasten to conclude our running survey by some mention of the recorded performance of this engine. The driving wheels being 5 feet in diameter, the tractive force would be pounds for each pound of effective pressure upon the pistons.
The author states that this engine "has drawn a load up an inclined plane that was equivalent to 220 tons gross weight upon a level (including engine and tender) at a velocity of 14 miles an hour, which appears to be about the extent of the power of the engine, with the steam at the usual pressure of 50 pounds per square inch in the boiler." Taking these figures, and using D. K. Clark's formula for the resistance, of , we find that about 46½ pounds net effective pressure must have been maintained in the cylinders.
The distance traversed under these conditions is not stated, and there is some reason to doubt whether the actual efficiency of the engine at all times came quite up to the figures quoted by the author. However this may be (and it would be ungrateful to criticise too closely), we cannot refuse our assent to his concluding paragraph, which remains as undeniably true now as
FIG. 5.—CROSS SECTIONS OF THE END PORTIONS
when it was written sixty years ago, that the "great power and velocity of the present locomotives could not have been obtained without the rapid means of generating steam afforded by the use of the tubes; and the tubes would have been useless without the powerful draught produced by the blast, which
