Rail-Eoads. 14; 



At 4 miles an hour, will require . 

 At 6 ditto ditto 



At 8 ditto ditto 



At 12 ditto ditto 



Or conversely : — 



100 pounds moves 90,000 pounds at 

 or 22, .500 at 



or 10,000 at 



or 5,620 at 



or 2,500 at 12 ditto 



Hence we see that when we have to contend with the re- 

 sistance of water, a great increase of power produces but a 

 small increase of velocity. To make a ship sail three times 

 faster, for instance, we must employ nine times the power ; and 

 to make her sail six times faster, we must employ no less than 

 tliirty-six times the power. Let us suppose, for example, that 

 it were required to determine, since one horse draws a boat 

 loaded with thirty tons at two miles an hour, how many horses 

 would draw the same boat at four miles. We find, first, that 

 since the boat is to move tisoo times as fast, it will requireyo2<r 

 times the absolute amount of power, or 400 pounds. But a 

 horse moving at four miles an hour, pulls only with a force of 

 64 pounds. Of course, it would require six horses to exert a 

 power of 400 pounds, and move the boat at the rate proposed. 



Let us now see what amount of power will produce corre- 

 sponding effects upon a rail-way. And before we make more 

 particular inquiry, let us suppose that the retardation occa- 

 sioned by friction, instead of increasing as the square of the 

 velocity like the resistance of a fluid, increases in the simple 

 ratio of the velocity. We have seen, then, that a force of 

 traction of 100 pounds upon a level rail-way, moves a body 

 weighing 30,000 pounds at the rate of two miles an hour. 

 We may hence calculate the effect produced by any greater 

 amount of power: — 



30,000 lbs. are moved at 2 miles an hour by a power of 100 lb, 

 at 4 miles ... by ... 200 lb. 



at 6 miles ,,. by ... 300 lb, 



at Smiles ,,. by ... 400 lb. 



at 12 miles ... by ... 600lb. 



Or conversely : — 

 A powcrof loo pounds moves 30,000lb. at 2miles per hour, 

 or 15,000 lb. at 4 

 or 10,000 lb. at 6 

 or 7, 500 lb. at 8 

 or 5,000 lb. at 12 

 Vol. 05. No. 322. /'rA. 1H25. T Henc^ 



