I

LIG

106

LIG

in lengths of nine feet, with flanges at the top and bottom,which are accurately turned and fitted together, so that theydrop on to one another; there is a projection.

“ The external water will he found to be effectuallyexcluded by such a mode of junction ?—Perfectly ; we neverhave a drop through them ; they require nothing more thana single coat of paint, and when we use one of the castingswe clean the flange carefully and give it one coat of good redj lead paint, and put another down upon it, which is preparedI in the same way ; they never leak a drop.

1 “ Do you recommend as a general principle the adoption

of a cylinder or of a square form ?—Generally a cylinder, forseveral reasons.

• “ Will you state the reasons ?—In the first place, because

j it is the cheapest form to construct in the preparation of thecasting itself; and, in the second place, because it is better! capable of bearing pressure, and therefore can be cast with. I a much less quantity of material in it; the object in a founda-tion being to get the largest bearing surface at the leastpossible cost; in the third place, because we have found inpractice that it is difficult to sink square caissons closetogether, because, having a very small space between them,j one having been sunk, it is very apt to make it difficult tosink an adjoining one ; we have no ground between themto work upon.

“ The Committee understand, likewise, that there is roundeach cylinder a girdle of timber, which is necessary in orderj to keep the cylinder in its perpendicular position ?—Yes ; I| have made use of piles upon which temporary frames arefixed, and put two rows of what we call wallings, forming ai square space, in which the cylindrical pile is placed andi driven by means of the pressure on the cap of the cylinder.

“ Are the Committee to undrstand that the surface, or thebed of the river, is in the first instance level, in order toreceive the cylinder ?—Not at all ; we deal with it as wefind it.

“ You use no mechanical means, except in the experimentto which you have adverted, of 30 tons and 100 tons ofactual weight; you have recourse rather to physical meansof exhausting the air, and of admitting the pressure of theatmosphere?—Yes, because it is so much cheaper. It is aserious job to put 30 tons on to a pile, whereas a simple cast-iron cap, as I have before described, put on to the top, is soexceedingly easy.”

In another part of his evidence, Mr. Fox says, “ There isno doubt that the cheapest foundation you can put in is touse the largest size cylinders, so as to have them within thecompass of ordinary means of moving about. If you had apile two feet in diameter it would bear a certain load, sup-posing it to be in any semifluid foundation ; if you doublethe diameter, you would only double the weight of thecylinder, but it would carry four times the load.” Again,—and this is peculiarly applicable to foundations on sands,&c., for lighthouses—“ If you give me a piece of ground, andfirst there is a layer of mud, and then a layer of gravel, andl then a layer of rock, and then a sheet of cast-iron, and thenanything else, I will put a cylinder through it. I also willbring up the foundations of the bridge to low-water level,

' for something like the same ( cost as would have beenexpended under the old plan, in the mere material used for' that purpose, saving coffer-dams altogether.”

Mr. Bush’s “Light of all nations,” though it failed so sig-nally, deserved notice. This was again a’proposal to con-I struct a lighthouse on the Goodwin, ever a locality for experi-| ments of this nature. The site at last chosen was, for any, good effect to be derived from it, as bad as could possibly be,neing on the middle of the sand, and consequently calculated

rather to lead vessels into danger, than to preserve themfrom it.

“ The Light of all nations ” was intended to he an irontower erected by means of an iron caisson, which was toafford the means of forming a substantial foundation. Thiscaisson, the frustum of a cone 30 feet in diameter, and 28feet high, weighing above 150 tons, was towed out from Dealby one of Her Majesty’s vessels to its station, about thecentre of the Goodwin Sands, on July 27, 1842. The caissonwas made water-tight, in order that, as it settled down, tboworkmen might he enabled to construct the foundation onthe chalk substratum of the sand. This substratum, however,was never reached ; the caisson did settle down, but not pet'pendicularly, and after it had been knocked about by severalgales of wind, it was found impracticable to carry out theoriginal design, and it was therefore necessarily abandoned-On the wreck of the caisson, however, Mr. Bush succeeded inerecting a smaller shaft, surmounted by a small light-roo®,and in this room he and his wife remained during a night inthe beginning of 1845.

The lighthouse was never completed. And the TrinityHouse was at last obliged to interfere, to prevent, fromdangerous situation, its being used as a light-beacon.

Another adaptation of iron to the construction of lighthouse 3has met with far greater success, and promises to be of thegreatest utility, whether as regards economy, or facility ° lconstruction. This is the iron lighthouse designed WMr. Gordon.

It is rather singular that iron should not have bee®employed in this' form before, when we consider the mult 1 'farious variety of purposes to which it is now applied. ^the year 1805, however, a cast-iron lighthouse was suggestedby Mr. Bennie, for the Bell-rock, and also by Mr. Bobe rStevenson in 1800. The first tower of this construct! 011 ’was erected on the eastern end of the island of Jamaica , °®,another of a similar kind for Bermuda . The latter isfeet 9 inches high, formed with iron plates, the entire weig 11 jof which is nearly 100 tons. The building has seven stoi'i® 9 ’ jand the lower portion is filled in with concrete to the lieig 11 iof 22 feet, to give it stability. Nearly every portion of toedifice is of iron, and the erection of the tower was compl etein ten months, finished October 9, 1845. These lighthouse^were constructed in London , put together and erected, aDthen taken to pieces again and forwarded to their destinati° n j

The light in the Bermuda lighthouse is from a beaut®dioptric first order apparatus, constructed by Messrs Wilk 1and Son, of Long Acre ; the lenses composing it were m a ^by M. H. Lepante of Paris , and is one of the most effi c,eand powerful lights in the world. ^

Having thus shown some of the different methods empleyj^in the erection of lighthouses, and the improvements wh 1modern art has introduced, we now turn to another imp° rtapart of our subject, that of the illumination of lighthouses-

The first lighthouses, such as the Cordouan , and the N 01Foreland, were illuminated by open fire-places, or chauuplaced on the summit of the towers. In the former, 1 ^burnt billets of oak-wood ; and in the latter, coal. It -

readily seen how incompletely such arrangements must

have

performed their office. Of course the time at which aligl 1 ^ 10 ^,}becomes most serviceable is, during tempestuous weather ^a wind blowing towards the land, causes that dread ^mariners—a lee-shore ; yet this wind would drive •>«»*»£<»an open fire away from the very direction in which they ' gmost required to be seen ; thus the bars of the grate "often nearly melted to leeward, while towards the sea ,coals remained untouched by the fire. One advantage) o ^ever, there certainly was sometimes in the open fire, vi*-» -