ENGINEERING. 295 



tion, and railroads were made, not to carry goods to the final destination, but to 

 a canal or other navigation. After the success of the Liverpool and Manchester 

 Railway in 1830, this opinion was seriously shaken, and in a short time canal 

 construction mostly ceased. Its era in this country was scarcely a quarter of a 

 century, between 1817 and 1835. 



Canals to be successful now must be capable of passing vessels of large ca- 

 pacity, must not have too much lockage, and the locks must be worked by steam 

 or water-power; the boats must be moved by steam, either on board, when the 

 vessels are large enough, or, when the vessels are smaller, by locomotive on the 

 bank, or by cable at the bottom, and then the locks must be large enough to hold 

 the fleet taken by one locomotive or cable power; there must be plenty of water, 

 and the canal must connect harbors or navigable waters. 



I tried towing by locomotive on the canal bank more than forty years ago. 

 There is, of course, no difficulty in one engine towing several boats, but if the 

 locks are not large enough to pass the whole fleet at once, the delay of all the 

 fleet till each boat is passed separately, counterbalances the economy of steam in- 

 stead of horse-power. The speed even for light boats cannot be increased to 

 more than five or six miles per hour on account of the wave. 



Cable-towing, notwithstanding the reported failure on the Erie Canal, can, 

 with proper boats and apparatus, and with experienced men, be easily performed 

 on the crookedest canal in America, as it is now done in Belgium. 



Canal engineering does not avail itself of the engineering resources of the 

 age. Little improvement is made in it : mainly, I suppose, because it is not con- 

 sidered worth improving. 



The most remarkable early river improvement in this country was that of the 

 Lehigh. About the year 181 7, Josiah White and Erskine Hazard commenced the 

 improvement of this river, and made other preparations to inaugurate the anthra- 

 cite coal trade. In 1820 they sent to market 365 tons, which was the beginning 

 of the regular anthracite coal trade of America. Now the annual amount will 

 soon reach 30,000,000 of tons. 



The descending navigation they made consisted, first, in clearing the chan- 

 nel of rocks and confining the water in the rapids, when low, to that narrow chan- 

 nel by boulder wing dams ; second, when the fall was too great for this, in build- 

 ing dams with bear-trap locks ; and third, in storing the water in pools, and let- 

 ting it run only when the coal arks were running. 



The bear-traps locks have given the hint for several devices since used, and 

 are well worthy of examination. Near each end of the lock was a pair of gates, 

 each gate reaching across the lock and to the back of the recess on each side, 

 which gates, when not damming back the water, lay flat on the bottom of the 

 lock. The lower gate could be made to revolve through an arc of somewhere 

 about 40 degrees around a horizontal axis coincident with its down-stream edge. 

 The upper gate of the pair, when laid flat, lapped over about half of the width of 

 the lower gate, and revolved through a similar arc around its up-stream edge. 

 When laid fiat, the water, of course, ran freely over them. They were raised by 



