MECHANICAL ENGINEERING, THE PROGRESS OF. 



545 



provements. The time will come when the 

 nuisance of flying dust and ciuder will be un- 

 known. The greatest of all modern inventions 

 in this department, the Westinghouse continu- 

 ous brake and the Miller platform and coupler, 

 have decreased the risks of journeying by rail 

 to a merely infinitesimal quantity. A train, 

 when at full speed, can be stopped within its 

 own length. Steel rails have driven out iron, 

 and this superior metal is slowly and surely 

 taking the place of its defective rival in boiler 

 and running parts. While Bessemer steel is 

 used for rails, open-hearth steel is coming to 

 be as exclusively used for all parts of the loco- 

 motive. 



The efficiency of the lute styles of stationary 

 engines is illustrated by figures like these : 

 Corliss obtains a duty, as recorded at a 12-hour 

 trial of his last Providence purnping-engine, of 

 113,878,580, without reduction or allowances, 

 and the average of several days' trial is 112,- 

 000,000. Leavitt shows a duty, for months 

 together, of about 105,000,000, and obtains a 

 horse-power with an expenditure of 16J pounds 

 of feed-water per hour at Lynn and 16'23 at 

 Lawrence. His Calumet engine, with wet 

 steam and but 200 feet piston speed, demands 

 but 18 pounds, and the Hecla hoisting-engine 

 is credited with 16 pounds.* 



This figure sixteen pounds of stearn per 

 hour and per horse-power may be put on rec- 

 ord as the very best economy attained by the 

 best engineers at the end of the decade 1870- 

 '80. It is just double the weight which would 

 be required in a perfect engine working steam 

 of the same pressure at maximum efficiency. 

 This leaves still a fair margin for further ad- 

 vance in the construction of the engine. The 

 steam-boiler is at a stand-still ; there is but 

 little margin for gain in economy, but a large 

 gain in weight of steam supplied per pound of 

 boiler may be expected when the tardily rec- 

 ognized advantage of forced circulation is se- 

 cured. 



Air and gas engines are competing with 

 stationary steam-engines, but in no other field. 

 The compressed-air engine, the petroleum-en- 

 gine, and the gas-engine are all just now com- 

 ing forward. The gas-engine sometimes con- 

 sumes as little as eighteen cubic feet of gas per 

 hour per horse-power. The solar motor pro- 

 posed by Ericsson has, as yet, made no prog- 

 ress beyond the plans and experiments of the 

 inventor. 



Little has been added regarding the theory 

 of heat-engines to the labors of Rankine and 

 Clausius, except in the minor branches of ther- 

 modynamics. In this field the practical work 

 of the engineer is to-day that of seeking, with 

 the aid of the physicist, to determine the facts 

 and the laws governing the exchange of heat 



* This is the more remarkable from the fact that the jack- 

 ed 



engines at Chicago, giving a duty of nearly 100,000,000 with 

 lower heads only jacketed, is similarly significant. 



VOL. xxi. 35 A 



between the working fluid and its inclosing 

 walls. Commercial efficiency is often made a 

 maximum with very much smaller engines, 

 and lower rates of expansion, than are found 

 to give maximum economy of fuel. Rankine 

 was the first engineer to base calculations of 

 economy on the aggregate of commercial con- 

 siderations instead of regarding only the single 

 aspect of economy in fuel. Thurston, as well 

 as other recent investigators, has applied this 

 method of calculating the efficiency of steam- 

 engines, on which he makes the following ob- 

 servations : 



"We are not, it is evident, to conclude, from tlie re- 

 sults of the application of the Eankine method of de- 

 termining size of engine and maximum commercial 

 efficiency, that we are always to lose so large a pro- 

 portion of the gain obtainable by further expansion of 

 steam. We conclude, rather, that the engineer must 

 direct his attention to improvements designed to re- 

 duce these counteracting wastes. He must find meth- 

 ods of rendering the machine, including boiler, au- 

 tomatic, and thus of reducing cost of attendance ; he 

 must find ways of reducing first cost, as by increasing 

 speed and making smaller engines do the work, as by 

 finding ways or building cheaply, yet doing good 

 work, and of making lubrication less costly, or of 

 doing away with it altogether. Automatic 'firing or 

 stoking, automatic feeds, and automatic cleaning ap- 

 paratus are already in use, as well as automatic regu- 

 lation of the engine, of steam-pressure, of point of cut- 

 off, and of chimney- draught. All these improvements, 

 when once made successful and thoroughly reliable, 

 will come in effectively to aid the engineer in this di- 

 rection, as well as the more direct advances in prog- 

 ress in the direction of reducing back pressure and of 

 checking cylinder condensation, of increasing steam- 

 pressure, superheating, and obtaining by the use of 

 all known methods ot high ratios of expansion at 

 maximum efficiency. The engineer and the physicist 

 working hand in hand in the future as they have in the 

 past or perhaps the engineer-physicist will sooner 

 or later, following the paths pointed out by Smeaton 

 and Perkins, and in our time by Corliss, 1 orter, and 

 Leavitt, greatly reduce the now often broad margin 

 between theoretical efficiency and commercial econo- 

 my. When the engineer has once acquired the habit 

 of gauging the value of an engine by the magnitude of 

 its ratio of expansion at maximum efficiency, all this 

 latter class o_f improvements will advance with in- 

 creased rapidity, and when he sees thattlie magnitude 

 of the ratio o*f expansion at maximum commercial 

 economy is a gauge of his success in making steam- 

 power useful, the first class of improvements and of 

 inventions will similarly advance, while we shall glad- 

 ly approximate to mechanical perfection, and this 

 progress will occur at a rate which will bo measured 

 by the approach of the two ratios of expansion to the 

 same maximum, finally both becoming nearly coinci- 

 dent with the ratio of 'maximum emciency of fluid for 

 each given case. 



The compound engine has become the stand- 

 ard type of steam-engine in nse on shipboard as 

 well as for stationary pnmping-engines. Occa- 

 sional intimations are heard that a counter- 

 revolution and return to the single cylinder type 

 of engine may be expected, but that change is 

 not observable. The direction and extent of re- 

 cent advances in marine architecture are readily 

 noted. The proportions of length of ship to 

 breadth remain, as during several years past, 

 about ten to one or eleven to one about fifty 

 per cent greater than has been considered by 

 some of the best engineers as that giving highest 



