* I 



30 ANNUAL OF SCIENTIFIC DISCOVERY. 



and put out of communication with the boilers. The valves were of 

 the ordinary double beat poppet kind, habitually used in American 

 paddle engines. The steam valves were made to act as expansion 

 valves, by means of an arrangement known as " Siekles's cut-off. 1 " 

 The distance between the boiler and engine was 2o feet : and the 

 total length of the steampipe over 17 inches in diameter, exposed to 

 the refrigerating inlluence of the atmosphere, was 30 feet ; and the 

 pipes being set on a slight incline, the water of condensation nat- 

 urally found its way into the cylinder. The steam pipes were 

 clothed with felt and wood lagging. The heads of the cylinders, 

 the valve chest, and the long nozzles, peculiar to this form of engine, 

 were without covering of any kind. It is needless to enter into any 

 minute detail of the experiments. We have already alluded to 

 Mr. Isherwood'' s talents, and he spared no trouble to obtain exact 

 results from the engine under trial. The vessel was moored fast, 

 the ice cut away from about the floats, and the whole power of the 

 engine exerted in paddling the water backwards. Each experiment 

 lasted 72 consecutive hours, during which the engine was neither 

 slowed nor stopped ; with the steam cut off at eleven-twelfths of 

 the stroke, the. consumption of coal amounted to 4'847 pounds per 

 hour: cut-off at seven-tenths to 4' 324 pounds; at four-ninths to 

 3'725 pounds, at three-tenths to 3'677 pounds ; at one-fourth to 

 S'428 pounds ; at one-sixth to 3'81 pounds ; and at four-fifths to 

 4*281 pounds. From these results we iind, that the gain by expan- 

 sion is decided up to a cut-off at one-fourth of the stroke, and that 

 there is no advantage to be derived from expansion afterwards, with 

 the po.rtlcnlar enr/ine imder consideration. The results perfectly 

 satisfied Mr. Isherwood. He prepared a very elaborate report,- 

 a model of its kind, in the course of which he attempts with 

 much plausibility to upset Mariote's law as applied to the expansion 

 of steam, and laid it before the Secretary of the Xavy. As a result, 

 it now appeal's, from the Washington investigation, that the engines 

 for the American Navy have been, almost from that day forth, 

 constructed without any regard to the carrying out of the principles 

 of expansion. The crop thus sown will be reaped erelong in 

 diminished speed, and in increased! coal bills. 



If the engine of the Michigan had been specially designed to 

 prove that the advantages of expansion were a delusion, it could 

 not possii.lv have been better adapted to the end. Mr. Isherwood 

 is a careful, and, we presume, a conscientious experimenter, but all 

 his conclusions in this case are vitiated by being drawn from false 

 premises, lie has recently published a large and handsome volume, 

 a large portion of which is taken up with a detailed account of these 

 experiments, and their analysis. It required little penetration to 

 see where the author has lamentably failed to make out a case. No 

 provision whatever, either by superheating or otherwise, was made to 

 prevent condensation in the cylinder of the Michigan's engine. 

 The length of the stroke was eight feet, the number of double strokes 

 per minute, with the steam at full pressure, was a little over 20; 

 with the steam cut off at one-fourth rather less than 14. The steam 

 had to traverse some 30 feet of steam pipe, lightly clothed, in an 

 atmosphere only raised above 29 by the heat abstracted from 



