Report on the Progress and State of Applied Mechanics. 223 



should not have been discovered until so late a period in the history of 

 canals. 



59. Canals form a connecting link between lines of conveyance for 

 passengers and goods, and Lines of Conveyance eoe Wateb. These 

 are either for drainage or for water supply. 



60. The principles of the deainage of labge districts of countet 

 have been studied and applied from a very remote period ; and their 

 progress has been so gradual, that it is difficult to fix on great leading 

 events in it. Perhaps the most striking work for that object in Britain 

 is the Great Bedford Level — a large and straight canal, which acts at 

 once as a channel and as a reservoir — collecting the waters of the dis- 

 trict during the intervals between low tides, and discharging them 

 rapidly at low water, through great flood-gates. 



61. The Deatnage of Towns has for some years been making rapid 

 progress, both as to the extension of its use, and as to improvements in 

 the art of laying out and constructing the drains. There is still, how- 

 ever, much room for further improvement. 



62. Along with the branches of sanitary engineering, that which 

 relates to Water supply has recently made great progress, not so 

 much in the magnitude of the works and of the quantities of water 

 supplied by them, in which the ancient Romans are .still unsurpassed, 

 as in the art of providing large supplies of pure water at a moderate 

 cost, whether by pumping engines, by the collection of water in artifi- 

 cial reservoirs, or by drawing it from a natural reservoir, such as Loch 

 Katrine, — a source of supply for this citj' originally proposed by Messrs. 

 Gordon and Hill. 



63. Lines of Contey^ance for Gas belong to a special branch of 

 engineering, so intimately connected with practical chemistry, that we 

 leave it to those who may report on that branch of applied science. 



64. Of Lines of Conveyance foe Signals, that which has super- 

 seded all others is the Electric Telegraph. The construction of 

 telegraphic lines on land is simple and well known, and has not recently 

 been marked by any great improvement. In long hnes of Submarine 

 Telegraph, a difficulty in making signals, arising from the electrostatic 

 charge of the conductor, was predicted from a theoretical investigation by 

 Professor William Tliomson, and means of overcoming that difficulty 

 were invented by Mr. Whitehouse. For such lines, batteries of great 

 power, and receiving instruments of extraordinary delicacy, are required ; 

 and in both these respects, the latest step in the march of improvement 

 has been made by Professor William Thomson, as is shown by his 

 instruments having succeeded in transmitting intelligible messages 

 through the damaged Atlantic Cable, when all other means had failed. 



