THE STEAM-ENGINE. 



535 



Manchester railway ; under the condition that it should produce no smoke ; 

 that the pressure of the steam should be limited to fifty pounds on the inch ; 

 and that it should draw at least three times its own weight, at the rate of not 

 less than ten miles an hour ; that the engine should be supported on springs, 

 and should not exceed fifteen feet in height. Precautions were also proposed , 

 against the consequences of the boiler bursting ; and other matters not neces- 

 sary to mention more particularly here. This proposal was announced in the 

 spring of 1829, and the time of trial was appointed in the following October. 

 The engines which underwent the trial were, the Rocket, constructed by Mr. 

 Stephenson ; the SanspareiJ, by Hackworth ; and the Novelty, by Messrs. 

 Braithwaite and Ericsson. Of these, the Rocket obtained the premium. A 

 line of railway was selected for the trial, on a level piece of road about two 

 miles in length, near a place called Rainhill, between Liverpool and Manches- 

 ter ; the distance between the two stations was a mile and a half, and the 

 engine had to travel this distance backward and forward ten times, which 

 made altogether a journey of thirty miles. The Rocket performed this journey 

 twice : the first time in 2 hours 14 minutes and 8 seconds ; and the second 

 time in 2 hours 6 minutes and 49 seconds. Its speed at different parts of the 

 journey varied : its greatest rate of motion was rather above 29 miles an hour ; 

 and its least, about lli miles an hour. The average rate of the one journey 



was 13 T % miles an hour ; and of the other, 14^y miles. This was the only 

 engine which performed the complete journey proposed, the others having 

 been stopped from accidents which occurred to them in the experiment. The 

 Sanspareii performed the distance between the stations eight times, travelling 

 22 J miles in 1 hour 37 minutes and 16 seconds. The greatest velocity to 

 which this engine attained was something less than 23 miles per hour. The 

 Novelty had only passed twice between the stations when the joints of the 

 boiler gave way, and put an end to the experiment. 



The great object to be attained in the construction of these engines was, 

 to combine with sufficient lightness the greatest possible heating power. The 

 fire necessarily acts on the water in two ways : first, by its radiant heat ; and 

 second, by the current of heated air which is carried by the draught through 

 the flues, and finally passes into the chimney. To accomplish this object, 

 therefore, it is necessary to expose to both these sources of heat the greatest 

 possible quantity of surface in contact with the water. 



The superiority of the Rocket may be attributed chiefly to the greater 

 quantity of surface of the water which was exposed to the action of the fire. 

 With a less extent of grate-bars than the Sanspareii, in the proportion of three 

 to five, it exposed a greater surface of water to radiant heat, in the proportion 

 of four to three ; and a greater surface of water to heated air, in the proportion 

 of more than three to two. It was found that the Rocket, compared with the 

 Sanspareii, consumed fuel, in the evaporation of a given quantity of water, 

 in the proportion of eleven to twenty-eight. 



The object to be effected in the boilers of these engines is, to keep a small 

 quantity of water at an excessive temperature, by means of a small quantity of 

 fuel kept in the most active state of combustion. To accomplish this, it is 

 necessary, first, so to shape the boiler, furnace, and flues, that the water shall 

 be in contact with as extensive a surface as possible, every part of which is 

 acted on, either immediately, by the heat radiating from the fire, or mediately, 

 by the air which has passed through the fire, and which finally rushes into the 

 chimney : and, secondly, that such a forcible draught should be maintained in 

 the furnace, that a quantity of heat shall be extricated from the fuel, by com- 

 bustion, sufficient to maintain the water at the necessary temperature, and to , 

 produce the steam with sufficient rapidity. To accomplish these objects, > 



