ON THE PROGRESS OP SCIENCE. IX 



construction of bridges, resulting from the use of iron ; and we have 

 only to examine those of the tubular form over the Conway and Menai 

 Straits to be convinced of the durability, strength, and lightness of 

 tubular constructions applied to the support of railways or common 

 roads, in spans which, ten years ago, were considered beyond the 

 reach of human skill. When it is considered that stone bridges do 

 not exceed one hundred and fifty feet in span, nor cast-iron bridges 

 two hundred and fifty feet, we can estimate the progress which has 

 been made in crossing rivers four or five hundred feet in width, with- 

 out any support at the middle of the stream. Even spans greatly in 

 excess of this may be bridged over with safety, provided we do not 

 exceed eighteen hundred to two thousand feet, when the structure 



<3 * 



would be destroyed by its own weight. 



" Importance of Good Machinery. It is to the exactitude and ac- 

 curacy of our machine-tools that our machinery of the present time 

 owes its smoothness of motion and certainty of action. When I first 

 entered Manchester, the whole of the machinery was executed by 

 hand. There were neither planing, slotting, nor shaping machines ; 

 and, with the exception of very imperfect lathes, and a few drills, the 

 preparatory operations of construction were effected entirely by the 

 hands of the workmen. Now everything is done by machine-tools, 

 with a degree of accuracy which the unaided hand could never accom- 

 plish. The automaton, or self-acting machine-tool, has within itself an 

 almost creative power ; in fact, so great are its powers of adaptation 

 that there is no operation of the human hand that it does not imitate. 



" Telegraphy. A brief allusion must be made to that marvellous 

 discovery which has given to the present generation the power to turn 

 the spark of heaven to the uses of speech ; to transmit along the 

 slender wire, for a thousand miles, a current of electricity that renders 

 intelligible words and thoughts. 



O <-> 



" In land telegraphy the chief difficulties have been surmounted, 

 but in submarine telegraphy much remains to be accomplished. Fail- 

 ures have been repeated so often as to call for a commission on the 

 part of the British Government to inquire into the causes, and the best 

 means of overcoming the difficulties which present themselves. I had 

 the honor to serve on that commission, and I believe that from the report, 

 and mass of evidence and experimental research accumulated, the public 

 will derive very important information. It is well known that three con- 

 ditions are essential to success in the construction of ocean telegraphs, 

 perfect insulation, external protection, and appropriate apparatus 

 for laying the cable safely on its ocean bed. That we are far from 

 having succeeded in fulfilling these conditions is evident from the fact 



