100 REPORT— 1841. 



was no danger of the Sound becoming more shallow, and that no further deposition 

 of silt or mud would take place, except immediately within or without the breakwater. 

 In consequence of a communication, made in July 1838, to the naval authorities at this 

 port, to the effect that a deposit was then going on in the Sound, the Admiralty di- 

 rected Mr. James Walker to report fully on the subject, and the best means for pro- 

 viding against the apprehended injury to the anchorage. After a long and laborious 

 investigation, and a minute survey, during which no less than 2000 soundings were 

 taken, Mr. Walker reported, that, taking the mean of the soundings that could be 

 affected by the breakwater, the result was that there was but very little increase or 

 decrease, and that, if there was any decrease of depth in the Sound (except close to 

 the br.;ak water, and which could produce no practical evil), this was certain, that if 

 it had taken place, it was but small, — certainly not enough to cause alarm, or to 

 justify expensive measures for removing the cause. As to the destruction of the break- 

 water by the Pholas, though connected with the breakwater since its commencement, 

 Mr. Stuart never saw a perforation in the limestone by the Pholas, except between 

 the low water of spring and of neap tides ; and these perforations only occur on the 

 outer surface of the stone, and to a depth not exceeding three inches. He never dis- 

 covered any such perforation in the interior of the work, although he had recently had 

 occasion to remove stones, by the aid of the diving-bell, at the depth of five feet be- 

 low low water, and which had been deposited there upwards of twenty-five years. 

 Loose stones had been taken up from beaches, and from the bottom of the Sound, 

 perforated by the Pholas, but they must have been perforated before they got there, 

 for the Pholas had never, in such cases, been found alive. 



On a Floating Breakwater. By Captain Taylor, B.N. 

 The breakwaters hitherto constructed have generally consisted of solid masonry, 

 thus presenting an unyielding obstacle to the waves, permitting accumulations of mud 

 and sand behind them, causing enormous outlay by the constant dilapidation from 

 the force of the waves and compressed air, and not affording the security to shipping 

 and life which is required, and maybe afforded by other means. The floating break- 

 water consists of floating sections framed of timber strongly moored ; these sections 

 yield to the shocks of the sea, and admit the waves to pass through them, and by thus 

 dividing the waves, reduce them to an open and harmless state. The depth of these 

 sections vary according to the situations in which they are employed. The sea in the 

 most tempestuous weather is said to be tranquil at the depth of sixteen or eighteen 

 feet below the surface ; a breakwater, therefore, immerged to that depth, and present- 

 ing six or eight feet above the surface, is sufficient to form a safe harbour on the most 

 boisterous coast. The angle of inclination which the section presents to the wave is 

 that pointed out by nature in the Mew-stone, viz. 35 degrees. Stone breakwaters 

 check the ground tides, and cause accumulations of mud and deposits which other- 

 wise would go seaward, and are peculiarly subject to the action of boring shells, con- 

 stantly at work below the dove-tailed stone ; and cavities being formed, large portions 

 are occasionally blown up. The destruction of the wood by the Teredo is prevented 

 in the floating breakwater by tarring the wood with a preservative mixture, and the 

 worm can make no lodgment on a prism floating upon the surface ; besides, it can be 

 scrubbed and tarred as often as required. The distinction between waves and break- 

 ers is very important, the former being an undulation, the latter being accompanied 

 with a translation of the mass, and capable therefore of exerting extraordinary forces 

 on the masses opposed to them, when applied force to force. The breakwater is 

 formed of hollow framework ; it fills with an inert body of water, which requires a 

 considerable force to be put in motion or driven through the breakwater, and each 

 succeeding wave expends its force upon the preceding, therefore each wave becoming 

 inert, acts as a resisting medium to the others, almost entirely independent of the 

 caisson itself, with but slight strain to the moorings, and thus passes broken and 

 tranquil to the inner or land side, which is rendered completely calm, instead of acting 

 with immense violence upon soUd masses. The construction of this breakwater is so 

 adjusted that its beam is limited to 20 feet, for beyond this it would present too solid 

 a resistance, and add to the strain on the moorings and framework. This was clearly 

 demonstrated by practical experiments. 



