532 



THE STEAM-ENGINE. 



which the engine rolled were furnished with corresponding teeth, which work- 

 ed in the teeth of the railroad, and, in this way, produced a progressive motion 

 in the carriage. 



The next contrivance for overcoming this fictitious difficulty, was that of 

 Messrs. Chapman, who, in the year 1812, obtained a patent for working a 

 locomotive engine by a chain extending along the middle of the line of rail- 

 road, from the one end to the other. This chain was passed once round a 

 grooved wheel under the centre of the carriage ; so that, when this grooved 

 wheel was turned by the engine, the chain being incapable of slipping upon it, 

 the carriage was consequently advanced on the road. In order to prevent the 

 strain from acting on the whole length of the chain, its links were made to fall 

 upon upright forks placed at certain intervals, which between those intervals 

 sustained the tension of the chain produced by the engine. Friction-rollers 

 were used to press the chain into the groove of the wheel, so as to prevent it 

 from slipping. This contrivance was soon abandoned, for the very obvious 

 reason that a prodigious loss of force was incurred by the friction of the chain. 



The following year, 1813, produced a contrivance of singular ingenuity, for 

 overcoming the supposed difficulty arising from the want of adhesion between 

 the wheels and the road. This was no other than a pair of mechanical legs 

 and feet, which were made to walk and propel in a manner somewhat re- 

 sembling the feet of an animal. 



A sketch of these propellers is given in fig. 63. A is the carriage moving 



Fig. 63. 



on the railroad, L and L' are the legs, F and F' the feet. The foot F has a 

 joint at O, which corresponds to the ankle ; another joint is placed at K, 

 which corresponds to the knee ; and a third is placed at L, which corresponds 

 to the hip. Similar joints are placed at the corresponding letters in the other 

 leg. The knee-joint K is attached to the end of the piston of the cylinder. 

 When the piston, which is horizontal, is pressed outward, the leg L presses 

 the foot F against the ground, and the resistance forces the carriage A on- 

 ward. As the carriage proceeds, the angle K at the knee becomes larger, so 

 that the leg and thigh take a straighter position ; and this continues until the 

 piston has reached the end of its stroke. At the hip L there is a short lever 

 L M, the extremity of which is connected by a cord or chain with a point S, 

 placed near the shin of the leg. When the piston is pressed into the cylinder, 

 the knee K is drawn toward the engine, and the cord M S is made to lift the 

 foot F from the ground ; to which it does not return until the piston has ar- 

 rived at the extremity of the cylinder. On the piston being again driven out 



