SECT, ix.] OF STEAM ENGINES. 285 



ridiculed, and some of the schemes for applying it not without reason. As 

 far as railways are concerned, it has however been proved to be applicable, 

 and with as few accidents as in any other of the varied applications of steam 

 power. 1 



591. OF THE APPLICATION OF STEAM POWER TO RAILWAYS. The power of 



steam may be applied by means of a fixed engine, or by a moveable one called 

 a steam carnage. 



FIXED ENGINES have been applied only in the case of inclined planes, and no 

 peculiarity is required in the construction of the engines, more than is wanted in 

 one for impelling a machine. Low pressure engines are generally employed for 

 this purpose ; and they are obviously the most safe and economical for the end, 

 unless when there is not a convenient supply of water. 



The motion of the engine ought to be equalized by a fly wheel, and it should 

 also be provided with a regulating valve. 



To proportion the power of the engine to the effect, the area of the piston 

 in inches, multiplied by the effective pressure on an inch in Ibs., should b e 

 equal to the resistance of the carriages added to the friction of the rope and the 

 engine. 



If A be the ascending, and D the descending load, and q the resistance from 

 friction at the axis, and i the angle of inclination, 



Then A (sin. i + q) D (sin. i - q) = (A D) sin. i + (A + D) q = the re- 

 sistance of the carriages. 



The weight of the rope or chain, and of the moveable parts of the engine, being 

 C, its friction and the stiffness of the rope may be represented by C S, hence, 



1 On common roads there are several circumstances which prevent the application of steam 

 power. The undulations of the road render it necessary to provide a power competent to ascend 

 the greatest inclination, and consequently an immense addition must be made to the weight of 

 the engine, so as to make the engine itself on an ordinary road consume half the power it gene- 

 rates. The resistance of these roads may be reduced by using larger wheels, as it chiefly arises 

 from the wheels sinking into the road ; and larger wheels afford a greater surface without increasing 

 the quantity to be depressed, while broad wheels give very little if any advantage. See my book 

 on ' Rail Roads,' p. 44. It may be proved, that no species of feet can be applied that will require 

 less power than plain wheels. An animal is contrived to move among obstructions, and when we 

 attempt to copy from the beautiful arrangements of our Creator, we should never lose sight of their 

 object. It is their perfect adaptation to the end, and their accomplishment by the most simple 

 means, that excites our admiration ; and the more we study the fine examples of the application of 

 power which nature affords, the more we feel the advantage of knowing the first principles which 

 determine the action of natural forces. 



