596 A century's progkess of the steam engine. 



construction. The standard was set up, it may be fairly asserted, by 

 Georg-e and Robert Stephenson about 1830. There is, however, far 

 less variation in the practice of reputable builders in this department 

 of steam-engine construction than in marine practice. It should also 

 be stated that in those earlier days there were occasions on which the 

 engines of the time were forced up to a speed which rivaled that of 

 similarly operated engines of our own daj^, as when George and Robert 

 Stephenson, in September. 1880, pushed the Rocket up to 36 miles an 

 hour, carrying the wounded statesman Huskisson to his home, 15 miles, 

 in twenty-five minutes. That engine was, in 1837, driven up to a speed 

 of 4 miles in four and one-half minutes on the Midgeholme Railway, 

 near Carlisle, a speed of nearly 55 miles an hour. 



Common practice during the last half century or more has ranged 

 from the ligures of Stephenson and his followers, as above, from 500 

 or GOO feet per minute piston speed, to about 1,000 at the close of the 

 century, while radicalh' high speeds may be taken as about 30 or even 

 50 per cent higher in cases of maximum speeds on special occasions. 



Steam pressures have been constantly rising since the time of Watt, 

 although, curiousl}' enough, some of the experimental work of the 

 inventors of the marine engine, as well as those of the locomotiA'e, has 

 been done with pressures of considerable magnitude, while the sta- 

 tionary engines of Jacob Perkins w^ere operated at pressures of from 

 1,000 to 1,500 pounds per square inch, and that inventor, about 183(5, 

 proposed pressures of 2,000 pounds. Dr. Albans a little later also 

 adopted pressures of 600 to 800 pounds and worked small engines 

 with, for a time, great economy and without any apparent difficulty. 

 Standard marine practice, however, like the steam pumping engine 

 practice of the early part of the century, involved the employment of 

 steam of little more than atmospheric pressure and permitted but very 

 tard}^ increase for man}^ years. 



Fig. 4 exhibits the general trend of this (change at sea, from the 

 earh^ part of the centur3% in vessels operated on regular routes. For 

 a long time the rise was extremely slow, but at about the middle of 

 the century the introduction of the surface condenser, by permitting 

 the use of fresh water in the boilers, or at least the avoidance of the 

 introduction of sea water, and by thus enabling the engineer to evade 

 the difficulties arising from constant precipitation of solid matter on 

 the heating surfaces of the boiler, caused the adoption of steadily 

 increasing steam pressures and allowed the designer to provide for the 

 utilization of the wider range of working temperatures which accom- 

 panied and gave reason for rise of pressure and larger thermodynamic 

 efficiencies. 



From that time the rise has lieen increasingly rapid, and the law of 

 increase with time is shown, with a fair approximation to the mean, t)y 

 the curve of the diagram. The increased pressure, in turn, made it 



