228

HISTORY OF ENGINEERING.

Book 1.

5 feet 3 inches from centre to centre, so inclined that at the top they were gathered intoa circle of about 6-4 feet diameter; the perpendicular height of this cone was nearly70 feet.

Each of the inclined timbers consisted in length of five or six pieces, arranged alternately :in those having five the lower length was 25 feet 3 inches, the second length 25 feet 10inches, the third 25 feet 4 inches, the fourth 24 feet 10 inches, and the fifth 30 feet 10inches; altogether 132 feet 1 inch. Where six lengths were used, the four lower pieceswere as those already described, the fifth was in length 24 feet, and the sixth 19 feet 7

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Fig. m

ELEVATION OK CONE,

inches. The scantling of the timbers at bottom was about 13 inches square, gradually dimi-nishing to 8 inches at the top : where they were joined, a dovetailed scarf was cut, 18 inches inlength, and the two ends were secured by iron bolts. Square holes or openings were left inthe timbers, 8 feet wide and 9 feet in height; one at the bottom for the purpose of admittingthe casks which floated it, and the other at the fifth course, to remove them when cut fromthe base and floated to the surface. After the inclined timbers were hoisted, which waseffected by a very ingenious process, they were bound together by six horizontal timberson the outside, and twenty-four on the inside. On the outside beech as well as oak wasused; in the first, third, fifth, and sixth courses oak, and in the second and fourth beech :these were scarfed at their ends, one 30 inches, and the oak 36 inches in length, and soplaced that they corresponded with the twenty-four internal horizontal timbers in the fol-lowing order:—

The first external with the first internal, the second with the fourth, the third with theeighth, the fourth with the twelfth, and the sixth with the twenty-fourth.

All the internal horizontals were halved 4 inches into the inclined timbers, and theirscantling was 13 inches square. Iron bolts with nuts and keys alternately were used tosecure them in their places.

A double course was afterwards added at the bottom to attach the casks, and ninety blockswere inserted between for the cables. After the slanting or inclined timbers were fittedtogether upon the platform, they were hoisted by eight pairs of shears, worked by as manygangs of men ; when the whole ninety were in their place the horizontal timbers werefixed, which when secured, the next length was raised, and so on till the whole wascompleted.

After this part of the operation was performed, other horizontal filling-in pieces wereintroduced, varying in scantling from 10 inches by 6 to 12 by 8, at the distance of about6 feet or 7 feet apart; fifteen of these were placed below water and as many above; theformer were fixed before the cones were floated, the others after they were sunk in theirrespective situations; the whole was secured by iron pins, which passed through theinclined timbers, and were fastened by nuts. Five circular courses, put round the interiorof the cones at the lower 36 feet of their height, prevented any injury when the casks wereattached.

The ninety ends of the timbers at the summit were capped by others 6 inches in thick-ness and 3 feet in width ; besides which other timbers were thrown across, radiating from acentre, acting as supports as well as forming a platform for the workmen.

This bold undertaking of Cessart attracted the notice of the most learned men of thetime, and numerous publications issued from the press condemnatory of the principlesavowed by the engineer, and for the purpose of frustrating the work. The sea, it was ob-served, was subjected to three great movements caused by the various winds, by the tides