A CENTUEy's PEOGBESS of the steam ENCimE. 595 



line has risen from -iO revolutions in 1840 to about luu or llu in J»yu 

 to 1899, and promises to become, in the best moderate practice 120 

 revolutio.is at the end of the century. The very largest marine 

 engmes, with their diameters ranging up to 3 and 4 feet in their hicrh- 

 pressure cylinders, and in low-pressure cylinders H and S feet, and 

 with their stroke of 5 or 6 feet, are now driyen up to 90 a.id 100 

 revolutions per minute with apparent safety, and un<iuesti(,nabiy crai„ 

 in economy and in reduced weight and volume. Medium poweVslind 

 sizes have similarly ranged from lOO to 200 revolutions, and •' positive 

 motion valve gears - and the small high-speed engines of torpedo 

 boats have carried radical practice in recent years up to .speeds of 

 rotation formerly incredible, now ranging all the way from 400 to <;00 

 revolutions. The steam turbine meantime has set a pace which even 

 the most radical t()rpedo-))oat constructors can never hope e\('ii to 

 approach with small engines— 5,000 to 10,000 revolutions per miiuite— 



FIG. -i.— PISTON SPEEDS OF LOCOMOTIVES 



their largest sizes probabU^ seldom falling much lu-low a speed of 

 1,000 to 2,000 revolutions. 



Fig. 3 exhibits the .speeds of pi.ston of the locoiuotivc from the 

 earlier days of its introduction to the present time; in this case, also, 

 the progress, practically, of the century. The lower line represents 

 what seems to have been considered .stnndard practice from the time 

 when there was such a practice; the middle line shows the advances of 

 the century in good common practice, and the upper line is that illus- 

 trating a high-speed practice. These deductions, however, are not to 

 be taken as either exact or controlling. The speed of the locomotive 

 is necessarily very variable, the character of its .service varies gn-atly. 

 and l)uilder,s are controlled by the.se varying conditions far more than 

 l»y any considerations of fuel saving. 



■ Ordinary i)ra.-tice became established about l.sr.o. after n.-arlx :i hall 

 century of experimentation and of variation of type and method ot 



