144 Rail-Ruads. 



power is employed, there is probably a loss of one-third in 

 consequence of the disadvantageous mode of its application. 



We see then that the effect produced by the draught of a 

 single horse is ten times as great upon a rail-way, and thirty 

 times as great upon a canal, as upon a well made road. Yet 

 a rail-way costs only iibout three times as much as a good 

 turnpike road*, and a canal about nine or ten times; and the 

 expense of keeping the rail-way and canal in repair is proba- 

 bly less in proportion to the original outlay than in the case 

 of a road. It is obvious, then, that were rail-ways to come 

 into general use, two-thirds or more of the ex})ense of trans- 

 porting commodities would be saved. With regard to the 

 comparative advantages of canals and rail-ways, so far as the 

 present facts go, we may observe, that if a horse-power effects 

 three times as much upon a canal as upon a rail-way, the canal 

 costs about three times as much, and will of course require 

 nearly the same rates or dues per ton to make the capital yield 

 the same interest. 



But here it is of great importance to recollect that this com- 

 putation refers solely to a velocity of tisoo miles an hour. If 

 the friction which impedes the motion of a car or waggon and 

 the resistance which the water offers to the progress of a ship 

 wei'e governed by the same laws, the same conclusions would 

 hold true whatever the velocity might be. But this is far from 

 being the case, as we shall presently see. In illustrating this 

 point, it will be convenient, instead of estimating effects by the 

 variable measure of a horse-power, to refer to a determinate 

 and constant force of traction of a given amount. W^e shall 

 therefore assume, that the body to be moved is urged forward 

 by force exactly equivalent to a weight of 100 pounds sus- 

 pended over a pulley at the end of the plane on which it moves. 



First, with regaixl to the motion of a body in water. It is 

 deduced from the constitution of fluids, and confii'med by ex- 

 periment, that the resistance which a floating body encounters 

 in its motion through the fluid is as the square of the velocity f. 

 Now, taking as a basis the known effectof force of traction of 100 

 pounds at two miles an hour, let us ascertain what force would 

 move the same body at a greater velocity. On a canal, or arm 

 of the sea, we have seen that a body weighing 90,000 jiounds 

 is impelled at the rate of two miles an hour by a force of 100 

 pounds; therefore, to move the same body 



* In Mr. Telford's estimates for portions of new road between Edin- 

 burgh and Wooller, we find the expense to be from one thousand to one 

 thousand one hundred pounds per mile, including the price of the ground. 



f See Playfair's Outline, i. 198 j Leslie's Elements, sec. vii. article " lie- 

 sislancc," Enc^'cl. Brit. 



At 



