Book II. 



RAILROADS. 



539 



441 



3455. Large blocks of granite (Jig. 44 1 . ) have been substi- 

 tuted for common-sized paving stones ; each block is two or 

 more feet square, nine inches deep, and channelled on the 

 surface in imitation of common-sized paving stones. These 

 are found to answ^er much better than the cast iron plates ; 

 but they are liable to the same objection as to leverage ; are 

 difficult to replace properly ; and as the raised pannels between 

 the grooves will in time wear down to the level of the grooves, 

 they cannot be considered so durable as common square stones; which after all appear the 

 best for general purposes, and at all events for paving the middle or sides of highways. 



3456. The defects of conwion pavement and the theory of its loear, are thus given by 

 Edgeworth. " Stones, in a common pavement, are usually somewhat oval, from five to 

 seven inches long, and from four to six inches broad. They are laid in parallel rows 

 on the road ifig. 442 c, d), or alternately (o, 6), as bricks are 

 laid in a wall. On the first sort of pavement wheels slip 

 from the ix)und tops of the stones into the joints between, 

 and soon wear away the edges of the stones, and their own 

 iron tire. By degrees, channels are thus formed between 

 some of the stones, and in time the pavement is ruined. 



3457. On the second sort of jmvement (a, b), where the 

 stones are placed alternately, to prevent the injury to which 

 the former method is liable, the wheel (f) sliding side- 

 ways, makes a channel between two stones, and is then 

 obliged to mount from the groove which it has made, to 

 the top of the stone opposite to it ; when it has attained 

 this situation, the wheel may slide sideways, or may go for- 

 ward over the top of the stone, till it drops into the inter- 

 stice between the two next stones. By continual wearing, 

 these ruts become so wide and deep, that the wheel does not touch the stones on either 

 side, nor does it reach the ground between them, but it bounds from one stone to the other, 

 thus jolting the carriage in every direction. This method is not at present in use. 



345.S. In the pavements hitherto described, the stones are but of a small size ; but if 

 flat Stones of twelve or fourteen inches long [e) are well laid, wheels are not liable to 

 slide into the joints ; and if such stones are laid with their longest sides crossing the road 

 they are less liable to injury; but still narrow wheels sometimes fall into the joints 

 between the largest stones, and having in time worn away their own edges, and those of 

 the stones, Ihey will act like wedges, and will displace the stones. No pavement, of the 

 best stone that could be pvocuied, can long resist this action of a narrow wheel. And 

 the only eflectual means of pieserving pavement is, to increase the breadth of all wheels 

 to at least three inches. Were no wheels narrower, a cheap and durable pavement might 

 be made of flat stones, not more than three inches square, provided they were eight or 

 nine inches deep, to givp them reciprocally lateral support ; for tlie tire of such broad 

 wheels could never sink between the joints of the stones. (Edgeworth.) 



Sect. V, Of Railroads. 



3459. Railwai/s or tramroads are not intended to be considered here as connected 

 with mines, canals, or other works which come directly under the province of the 

 higher branches of engineering ; but merely as substitutes for the whole or a part of 

 the metalled surface of common roads. The necessity of an expeditious and cheap 

 mode of conveying coals from the pits to the ships, had, as early as the year 1680, 

 introduced the use of wooden railways, for Ihc waggons to move upon, between the 

 Tyne river and some of the principal pits, and these by degrees became extended to 

 a great number of other coal-works. They were first solely employed for transporting 

 coals to a moderate distance from the pits, to the places where they could be shipped, 

 being universally made of wood. By degrees they were, however, carried to a farther 

 extent ; the scarcity of wood, and the expense of their repairs, suggested the idea of 

 employing iron for the purposes of improving these roads. At the first, fiat roads of 

 bar-iron were nailed upon the original wooden rails, or as ihey were technically called, 

 sleepers ; and this, lliough an exijcusive process, was found to be a great improvement. 

 But the wood on which these rested being liable to rot and give way, some imperfect 

 attempts were made to make them of cast iron, but these were found to be liable to 

 many objections, until the business was taken in hand by Outram, an engineer at Butterly 

 Hall, Derbyshire, who contrived at the same time, so far to diminish the expense, and 

 improve the strength of the road, as to bring them to a degree of perfection, that no 

 one who has not seen them can easily conceive could have been done. This having been 

 carried into execution in a few cases, and found to answer, has been improved upon 

 and simplified by practice, till it is now brought to such a state of perfection as to have 



