THE LOCOMOTIVE. 



must be visited ; to see those adapted to useful machinery, we must 

 go to the factories ; to view those applied to navigation, we must 

 descend into the holds o^ ships. The locomotive, however, needs 

 not be sought. It is patent and obtrusive. It addresses the 

 senses of hearing and seeing. The warning whistle and the 

 snorting chimney are familiar to every ear, and the flashing speed 

 of the engine, with its snake-like appendage of vehicles of tran- 

 sport, is familiar to every eye. 



2. Of the countless multitudes in all civilised countries who 

 witness the extraordinary performances of the locomotive, and 

 participate in its use and enjoyment, few comprehend the source 

 of its power, or the principle of its action. They see it sweep 

 along with the speed of the hurricane, drawing after it carriages, 

 carrying hundreds of human beings, or hundreds of head of cattle, 

 or tons of goods, but the agency which accomplishes this miracle 

 is to them wrapt in mystery. Many desire to possess the key to 

 the enigma, to unlock the secret, but recoil from the labours 

 which the perusal and study of even the most .popular treatise on 

 the locomotive would require, a labour for which few have the 

 disposable time, and still fewer the qualifications depending on 

 preliminary knowledge and intellectual aptitude. 



3. It is this nmltitude that we now desire to address, hoping 

 to offer, in a small compass, such a simple and clear account of the 

 variety of steam-engine referred to, as will be intelligible to all 

 persons, without more labour than all can conveniently devote 

 to it. 



4. A moving power may be applied in two ways to propel a 

 vehicle supported OB wheels. It may be harnessed to it as horses 

 to a carriage, and may draw it on by traces, or it may be applied 

 to the wheels, so as to make them revolve. If the wheels be made 

 to revolve, they must either slip upon the road, or the vehicle 

 must advance. But if the weight upon them be considerable, and 

 the state of the road suitable, they will have such adhesion with 

 the road at the points where they rest upon it, that they will not in 

 general slip ; and if they do not, the vehicle which they support 

 must be propelled by each revolution of the wheels through a space 

 equal to the external circumference of their tires. 



5. Now it is by this latter means that the power of steam is 

 applied to propel the locomotive. The steam pistons are connected 

 by iron rods, called connecting-rods, either with the spokes of the 

 wheels, at certain regulated distances from the axles, or with 

 arms, called cranks, formed on the axles between the wheels. 

 The force with which the pistons are alternately driven by the 

 steam from end to end of the cylinders, is conveyed by the con- 

 necting rods to the spokes or cranks, and it acts upon them in the 



114 



