CHAP. XII. 



OPERATIONS BEGUN. 



223 



circle of nearly double the area has been secured ; and 

 consequently the pressure of the foot upon every unit of 

 ground upon which the horse stands has been reduced 

 one half. In fact, this contrivance has an effect tanta- 

 mount to setting the horse upon eight feet instead of four. 



Apply the same reasoning to the ponderous locomotive, 

 and it will be found, that even such a machine may be 

 made to stand upon a bog, by means of a similar 

 extension of the bearing surface. Suppose the engine 

 to be twenty feet long and five feet wide, thus covering 

 a surface of a hundred square feet, and, provided the 

 bearing has been extended by means of cross sleepers 

 supported upon a matting of heath and branches of 

 trees covered with a few inches of gravel, the pressure 

 of an engine of twenty tons will be only equal to about 

 three pounds per inch over the whole surface on which 

 it stands. Such was George Stephenson's idea in con- 

 triving his floating road something like an elongated 

 raft across the Moss ; and we shall see that he steadily 

 kept it in view in carrying the work into execution. 



The first thing done was to form a footpath of ling or 

 heather along the proposed road, on which a man might 

 walk without risk of sinking. A single line of tem- 

 porary railway was then laid down, formed of ordinary 

 cross-bars about three feet long and an inch square, 

 with holes punched through them at the end and nailed 

 down to temporary sleepers. Along this way ran the 

 waggons in which were conveyed the materials requisite 

 to form the permanent road. These waggpns carried 

 about a ton each, and they were propelled by boys 

 running behind them along the narrow bar of iron. 

 The boys became so expert that they would run the four 

 miles across at the rate of seven or eight miles an hour 

 without missing a step ; if they had done so, they would 

 have sunk in many places up to their middle. 1 The 



1 When the Liverpool directors 

 went to inspect the works in progress 



on the Moss, they were run along the 

 temporary rails in the little three-feet 



