370

HISTORY OF ENGINEERING.

Book I.

Two courses of solid oak timber, squared, were laid one upon the other, to form thebasement; and on this five courses of Cornish moorstone, each a foot in thickness; thesewere well jointed, but laid without any mortar or cement, and retained in their placeby iron cramps ; the outer courses beingfurther bound together by upright ones,which also prevented their being lifted bythe action of the waves.

After this 5 feet of moorstone was laidon, which weighed 120 tons; two othercourses of timber crossed them, and wherethe timbers presented their ends, circularor compass timbers were laid, which werescarfed together, each course breaking jointover the other ; these outside timbers werejag-bolted to the interior parallel pieces.

Above the basement so constructed, awell-hole, 6 feet 9 inches square, was leftfor the stairs; and at 8 feet above thehighest part of the rock commenced thestep of the entrance doorway.

After constructing the building withcourses of moorstone and layers of compasstimbers up to the top of the central mast,the height of which was 33 feet, a floorwas laid over the whole, composed of 3-inchoak plank.

The upper part of the building com-prised four rooms, one over the other,formed of upright timbers, having a kerbor circle of compass timber on each floor,to which the upright timbers were screwedor connected, and upon which the floortimbers rested. These upright timberswere jag-bolted and trenailed to oneanother, and in this manner the whole wascarried up to the height of 34 feet abovethe floor, which was placed over the top ofthe central mast. The floor of the lanternwas made of 3-inch oak plank, aroundwhich was fixed the balcony.

The whole building was in form thefrustum of a cone, 22 feet 8 inches in di-ameter at the bottom, and 14 feet 3 inchesat. the top, and the height above the cir-cular base was 61 feet; so that the basewas a little more in diameter than one-third of its height, and the diameter attop was somewhat less than two-thirds ofthe base at the greatest circle. "Hie up-right timbers were united at the ends byscarfing and overlapping; they varied inlength from 10 to 20 feet, but were sounited that no two scarfings came closetogether. The number of uprights aroundthe entire building were 71, their breadthat the bottom nearly 12 inches, and theirthickness 9 inches, diminishing towards thetop, both in breadth and thickness. Allthe outside seams were well caulked with^oakum, and well pitched. The weight ofthe various beds of moorstone was calcu-lated to be 270 tons, and served to act asballast to keep steady this work of ship-carpentry. All the windows, shutters, anddoors, were composed of double plank, Fig. 3<2.crossed and clamped together; they shut into a rabbet, so that there was no crevice left forthe sea-water to penetrate.

Rl’DYERD S LICiiJTHOl'SE.