MECHANICS AND USEFUL ARTS. 51 



In weight from 10 tons downward, have been deposited in the sea, and 

 the rate at which this gigantic operation is carried on is said to be 

 from 22,000 to 27,000 tons per week, and from 4,000 to 5,000 tons per 

 day. 



The quarries which have been opened to supply so prodigious a de- 

 mand for material wherewith to control the waves are hardly less re- 

 markable objects of attention than the undertaking to which they are 

 subordinated. They realize the fabulous stories of mountains removed 



w 



and cast into the sea. As much as four tons of powder is frequently 

 exploded in them at one blast, or (more properly expressed) in one 

 mining operation, and thus 20,000 and 30,000 tons of stone are often 

 at once set free for the construction of the breakwaters. The plan 

 adopted is to blow away a huge section of the base of the mountain, 

 when the superincumbent mass of rock, 150 feet high, being unsup- 

 ported, tumbles down after it. The reader may form some conception 

 from these details of the manner in which the works are carried on ; 

 but it will quicken his appreciation to state that the rate of progress is 

 250 times greater than it was in the Plymouth breakwater. This 

 great economy of time has been effected by the use of piled stages 

 carrying railways, which, projecting boldly into the sea, present a me- 

 chanical arrangement for conducting the operations at once simple, 

 convenient, and independent both of tides and wind. Mr. Eendel was 

 scouted as a visionary when he first proposed so daring a plan for 

 facilitating the work, and it was confidently predicted that rails thus 

 supported on scaffolding would never answer. Nor is it wonderful 

 that persons less experienced than Mr. Rendel should have such mis- 

 givings, for the piles which support the stages are 89 feet long, being 

 built of short lengths of the timber commonly used for building pur- 

 poses. Thus, resting upon a precarious framework of wood, with 

 water more than 40 feet deep below, and required to carry long 

 trains of heavily loaded trucks, the railways of the Holyhead break- 

 water do not impress an unprofessional mind with any extraordinary 

 confidence in their security. There is, however, no answer to the 

 successful experience of four years in this matter, during which time 

 thousands of tons of stone have been daily brought down from the 

 quarries and deposited in the sea. A large proportion of the material 

 thus removed consists of fragments of rock weighing from 5 to 10 tons 

 each, and calculated by their weight to overcome, with the least pos- 

 sible delay, the momentum of the ocean. It may therefore be readily 

 conceived how severely Mr. Rondel's bold plan for carrying on the 

 works has been tested, and how complete his triumph has been. The 

 contract under which the harbor is being constructed contemplates 

 an expenditure of about 800,000, and the outlay so far is under 

 400,000. 



NEW BREAKWATER. 



A new system of floating breakwaters, especially adapted for the 

 Goodwin Sands, has been invented by Admiral Tayler of England. 



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