312
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was commenced on 12th August, 1812, agreeably to aReport dated 21st April, 1806 , of the late John Rennie ,civil engineer, and of Joseph Whidbey, a Master of theRoyal Navy ; and has been constructed under the auspicesof the Lords of the Admiralty. Its length is 5,100 feetat the top, and about 1 mile, or 5,280 feet at bottom,being nearly three times the length of the ExhibitionBuilding. At the top, it is 45 feet wide, and has a slopeto seaward of 5 to 1, and a slope to landward of 2 to 1.It is already composed of 3,768,879 tons of stone. Ithas been 38 years in construction, and has cost thenation about 1,500,0001. The area of Plymouth Soundis 1,800 acres, and within the breakwater there is anchor-age for 40 line-of-battle ships, besides a fleet of merchantvessels. The exhibitor of the model, who is the residentengineer, has been connected with this undertaking for40 years. The lighthouse and beacon on the break-water were designed by Messrs. Walker and Burgess,civil engineers.
Polished marble slab, on pedestals, from the break-water quarries.
Model, in limestone, of a general section taken througha part of the centre of the breakwater, with wood-jettyand crane, showing dove-tailed stones and truck on jetty.
Model, in limestone, of a section of the breakwater,taken through the buttress and foundation of the light-house, with inverted arch at the west end; and showingdove-tailed stones.
Circular lewises, used in lifting and setting stones atthe breakwater, invented by the exhibitor in 1808.
Model, in mahogany, of a breakwater stone vessel.
Models of the breakwater and lighthouse, set in marble.{Main Avenue West.)
[The breakwater in Plymouth Sound is formed by thedeposit of stone in unshapen blocks of various sizes, butdisposed upon a regular plan, as a huge, rough, broad-based wall, mole, mound, or dike, massive enough, if itbe compact enough, to check, if not wholly to stop theroll of the sea under the influence of gales of wind, and torender the part of the Sound within it a safe anchorageduring gales from the south-west.—The Isle of Wight isa breakwater afforded by nature to Portsmouth, and thebreakwater in Plymouth Sound is the result of an endea-vour to supply Plymouth with some compensation for itsnatural deficiency in that respect.
The breakwater is a mass of rock-like blocks of stonesdeposited in a heap at random, as far as regards theplacing of the blocks of stone, though the heap takesthe form, in plan and section, which the model exhibits.In this circumstance, that it is a deposit and not aconstruction, the weakness of the breakwater consists.The blocks on the outer slope, or foreshore, are liableto be taken up singly and displaced by the action of thesea upon it, deprived as every loose block is (and thebulk of the work still consists of loose blocks) of two-fifths of its weight when immersed in sea-water; andprobably no heavy sea runs into Plymouth Sound with-out occasioning change of place to some of the blocks ofthe outer slope. The blocks range from one ton to fivetons in weight—a block of limestone weighing five tons,being in bulk equal to a cube of 4 ft. 6 in., or a yard anda half on every side. The greatest quantity of the ma-terial is of the smaller sizes, and is known as rubble ; butmany blocks have been deposited of considerably greatersize than the largest size named, and many even of thesehave been known to be taken up by the sea from theouter slopes and thrown upon the crest of the mound;whilst thousands of tons have, since the commencementof the work, been thrown over the mound from the outerto the inner slope. It may be questioned whether thebreakwater is not at this time, from this cause, furtherup the Sound than it was originally placed.
The breakwater is disposed in three connected com-partments—the central, or main body, which is 1,000yards long, and the eastern and western parts respectively,which are each about 350 yards long, at the level of highwater.
The Digue , or breakwater, at Cherbourg, opposite toPlymouth on the other side of the Channel, is, in likemanner, mainly a mass of deposited rubble, but of gene-rally smaller-sized stones. It is more than double thelength of Plymouth Breakwater, or about 2j miles long,-w. H.] _
29 The Royal Scottish Society of Arts, Edinburgh —Producer.
A square bar of Low Moor iron, of superior quality,2} inches square, twisted, in a cold state, into a spiralform by the action of the steam-engine, while carryingthe borer of a cylinder which had suddenly stuck fast.
Model of a suspension bridge, designed to show thebest position of the under stays (which are not placedsymmetrically, but at irregular distances from either endof the bridge) to prevent the destructive effects of verticaloscillation.
[After the most careful calculation of the strength ofiron, when subjected to the application of force, in thedirection of its length, or its tensile resistance, bridgesonstructed of iron chains and rods, which promised tocast as long as those made of stone, have suddenly givenway. The principal cause of the sudden disruption ofthe rods or chains of an iron suspension-bridge, and itsconsequent fall, is the tendencyt o vibration or oscil-lation in the whole structure from its uniformity andcatenarian form. A chain-bridge, from its very nature,has a tendency to swing to and fro, and unless this beprevented by ties or fastenings to some rigid structurefixed in the ground, it will, after a certain number ofregular oscillations, snap in two at the weakest part, inconsequence of the momentum acquired by the swingingmass.—K. W.]
Model of a steam-boat, constructed for an inkstand.
30 Roebuck, Josephus Jagger, Huddersfield— Producer.
Model and drawings of No. 4 skew arch of the Hud-dersfield viaduct, built in stone, over the Bradford Road.Scale one inch to three feet.
Model of one of the springer quoins, showing theoblique checks for the insertion of the voussoirs of thespiral courses of masonry.
Model of springer course complete, showing the wholeof the checks.
Models of two of the arch quoins, showing the formand twist of Nos. 4 and 5 arch quoins of the obtuse angleof the arch.
Model of one of the spiral courses of the voussoirs.showing the spiral plane from the acute angle of the arch.
Drawing of No. 4 skew arch of the Huddersfielviaduct, by which the above model and detail modelwere constructed. Scale one inch to six feet.
[Skew, or oblique arches, are those the faces of whichare not at right angles with the abutments. It is believethat the first skew bridge was built by Mr. W. Chapmamin 1787, over the Kildare Canal, near Naas, q'hemetho ^of finding the directions of the courses of brickwork mmasonry, and the shapes of the various moulds forlatter, are explained fully in treatises on oblique arches.—S. C., jun.]
31 Hurwood, George, College Street, Ipswich , Suffolk
Inventor and Patentee. j
Window made to open and close in one or in se lj ge( jparts by the application of the patented apparatus,for ventilating the Exhibition Building.