THE STEAM-ENGINE. 



561 



plates forming the springs of the driving-wheels are thirteen in number, each 

 of which is four inches in width, and ygths of an inch in thickness. The 

 springs upon the other wheels are three inches in width. The springs of 

 the driving-wheels are below the axle, while those of the smaller wheels are 

 above it. 



Buffers D" are placed behind the tender, which act upon a spring C, fig. 70, 

 to break the collision, when the wagons or carriages strike upon the tender, 

 and similar buffers are attached to all passenger-coaches. Some of these buf- 

 fers are constructed with a system of springs similar to C, but more elastic, 

 and combined in greater number under the framing of the carriage, so that a 

 considerable play is allowed to them. In some cases the rods of the buffers 

 are made to act upon strong spiral springs inserted in the sides of the framing 

 of the carriage. This arrangement gives greater play to the buffers ; and as 

 every coach in a train has several buffers, the combined effect of these is 

 such, that a considerable shock given to either end of the train may be ren- 

 dered harmless by being spent upon the elasticity of these several systems of 

 springs. 



In order to give notice of the approach of a train, a steam-whistle Z', figs. 

 67, 71, is placed immediately above the fire-box at the back of the engine. 

 This is an apparatus composed of two small hemispheres of brass, separated 

 one from the other by a small space. Steam is made to pass through a hol- 

 low space constructed in the lower hemisphere, and escapes from a very nar- 

 row circular opening round the edge of that hemisphere, rushing up with a 

 force proportional to its pressure. The edge of the upper hemisphere pre- 

 sented downward encounters this steam, and an effect is produced similar 

 to the action of air in organ-pipes. A shrill whistle is produced, which can 

 be heard at a very considerable distance, and, differing from all ordinary sounds, 

 it never fails to give timely notice of the approach of a train. 



The water-tank I", figs. 68, 70, which is constructed on the tender, is 

 formed of wrought-iron plates J of an inch thick, riveted at the corners by 

 angle-iron already described. This tank is 9 feet long, 6f feet wide, and 2\ 

 feet deep. The top is covered with a board K", and a raised platform N" is 

 constructed behind, divided into three parts, covered with leads, which open 

 on hinges. The middle lid covers an opening to the tank by which water is 

 let in : the lids at either side cover boxes in which are contained the tools ne- 

 cessary to be carried with the engine. The curved pipe P", fig. 68, leading 

 from the bottom of the tank to the pipe Q", is of copper. The pipe Q", con- 

 necting the latter with the feed-pipe K', fig. 69, is sometimes formed of leather 

 or India-rubber cloth, having a spiral spring on the inside to prevent it from 

 collapsing. It is necessary that this pipe Q" should have a power of yielding 

 to a sufficient degree to accommodate itself to the inequalities of motion between 

 the engine and tender. A metal pipe is sometimes used, supplied with a double 

 ball and socket, and a telescopic joint, having sufficient play to allow for the 

 lateral and longitudinal inequalities of motion of the engine and tender. The 

 weight of an engine, such as that here described, supplied with its proper 

 quantity of water and fuel, is about 12 tons : the tender, when empty, weighs 

 about 3£ tons ; and when filled with water and fuel its weight is 7 tons. The 

 tank contains 700 gallons of water, and the tender is capable of carrying about 

 800 weight of coke. This supply is sufficient for a trip of from thirty to forty 

 miles with an ordinary load. 



It is not usual to express the power of locomotive-engines in the same man- 

 ner as that of other engines by the term horse-power. Indeed, until the actual 

 amouut of resistance opposed to these machines, under the various circum- 

 stances in which they are worked, shall be ascertained with some degree of 



VOL. 



36 



