306 Mb POWER, ON THE PREVENTION OF THE 



engines, both having their steam turned off, were started with the same 

 velocity, the lighter would be retarded more rapidly than the heavier. 



If indeed we assume that the machinery is similar in both, the prin- 

 ciple will be readily allowed ; for the rapidity of the retardation will be 

 as the retarding causes directly, and as the mass of the engine inversely. 



The principal retarding causes when the steam is turned off are, 

 1st, the resistance of the air ; 2dly, the friction of the parts of the 

 machinery sliding over one another, the principal of which is, probably, 

 the friction of the pistons within the cylinders ; 3dly, the roughness 

 of the rail, that is to say, such retarding causes as may act in the man- 

 ner of minute obstacles lying upon it ; 4thly, the friction on the axes. 



Now, though the effect of the two last causes will be nearly as 

 the masses of the engines, the two former may be regarded as pretty 

 nearly the same, the machinery of the engines being supposed similar 

 in the two cases ; on the whole, therefore, the retarding causes in the 

 smaller engine will be diminished in a less ratio than its mass ; it will 

 consequently be retarded more rapidly than the other. 



Let us now apply the principles which have been laid down to the 

 case before us. 



It will be recollected that the engines were connected by a chain, 

 which admitted of being tight or loose as the distance between them 

 was greater or less: it will be recollected also, that the pilot engine 

 was described as "top-heavy", which makes it highly probable that 

 the frame, to which the chain is usually applied at the middle, and 

 the buffers, (or disks which are brought in contact when the engines 

 approach each other), at the two sides, was considerably lower than 

 the centre of gravity of the engine. Lastly, it will be recollected, 

 that the steam of the large engine had been previously turned off. 

 Let us now consider what will take place when the steam of the small 

 engine in front is turned off. 



The small engine being retarded more rapidly than the large one 

 following it, the engines will be brought nearer and nearer to each 

 other, the connecting chain in the mean time becoming slacker and 

 slacker, and by the time the buffers are brought in contact, a finite 



