This plan of a stone dike or Breakwater being laid in detail before the Minister of Marine, it was deemed proper, on a subject so entirely novel, and of such great national importance, to consult the ablest men in France, before any steps should be taken for carrying it into execution. - The details were ac cordingly submitted to the four commissioners, M. de Borda, a naval officer and Member of the Acade my of Sciences ; M. de Fleurieu, Capitaine de Vais seau, and Director of Ports and Naval Arsenals, afterwards Minister of Marine; M. Peronnet, Mem ber of the Academy of Sciences, Chief Engineer of Bridges and Embankments ; and M. de Chezy, In spector and Director of the School of Engineers. They recommended that, in the first instance, an . experimental cone should be constructed, and float ed off. Instead, however, of 60 feet in height, the eone made at Havre was only 86 feet ; the circum ference of its base 472 feet, and having a slope of 60 degrees ; the upper circumference was 839 feet. Within the exterior cone, and at the distance of 5 feet 10 inches from it, was an interior and concentric cone, bound together by beams of wood, pointing to the common centre, each being the section of the radius. The frame of each cone was composed of 80 large upright beams, 24 feet long and 1 foot square. On these were erected 80 more, of 14 feet in length, making in the whole 820 of these large uprights ; the machine was then planked, hooped, and firmly fixed together with iron bolts.
The cone at Havre being completed, the next operation was to tow it off to the particular spot where it was to be sunk. Being open at the bottom, it was found necessary to attach to the lower circum ference 284 large casks, part to the exterior and part to the interior cone ; besides 50 casks, attached by lines of equal lengths, from the bottom of the inner circle, to float towards the centre, and thus assist in keeping it upright and steady. It was easy enough, by these means, to float off a vessel of this kind. M. de Cessart observes, that the force of 7200 pounds ?reduced by a capstan, was found sufficient to draw it on the water, to a dstance equal to the length of its own diameter, or about 25 toises, in two minutes.
" The success of the experiment made at Haire," says M. Curt, " had inspired such veneration for the conical .caissons, that those persons who had been most disposed to object to the plan, were now oblig ed to be silent." The result of the experiment at once decided the Government to commence opera tions at Cherbourg. M. de Cessart was appointed director of the works, with four Engineers to assist him. A permanent council, consisting of Command ers in Chief, Directors, Engineers, &c. was ordered to reside, for six summer months, at Cherbourg, and _ the other six in Paris; and a considerable body of - troops down to the neighbourhood, to furnish a competent number of artificers and labour ers, to be employed on this great national undertaking.
In 1788, the buildings were commenced for lodg ing the principal officers of the civil and military de partments, and their respective establishments ; a naval yard marked out and of com munication opened with the forts,—and at Becquet, about a league to the eastward of Cherbourg, a small harbour was dug out for the reception of about 80 vessels, which were to be employed in transporting the stones from thence by sea. • On the 6th June 1784, the first cone was floated off and sunk, and the second on the 7th July follow ing, in presence of 10,000 spectators, assembled on the shores and quays of Cherbourg ; but before the cavity of the latter could be filled with stones, a storm, in the month of August, which continued five days, entirely demolished the upper part of this cone. In the course of this summer the quantity of stones sunk within the cavities of the two cones, outside their bases, and in the intermediate space, amounted to 4600 cubic toises, or about 65,000 tons.
In 1785, three more cones were completed and sunk at irregular intervals ; and, at the end of that year, the quantity sunk amounted to 17,767 cubic toises, or about 250,000 tons. In 1786, five addi tional cones were completed and sunk ; one of them in presence of the King; and the quantity of stones thrown within them, and deposited on the dike con. necting the cones, amounted, at the end of this year, to 42,862 cubic toises, or 600,000 tons. In 1787, five more cones were sunk and filled with stones, making, in the whole, fifteen ; and the distance be tween the first and fifteenth cone was 1203 toises, and the quantity of stones deposited within these cones and the connecting dike, at the end of this year, amounted to 71,585 cubic toises, or more than 1,000,000 tons. The violent gales of wind that were frequent in November and December, carried away all the upper parts of the five cones which were sunk this year. In 1788, three more were sunk, but the upper parts of the first two were carried away as the others had been ; the height of the third was, therefore, reduced, so as to be, when sunk, on a level with low water; but this cone was upset and soon went to pieces.
The enormous expence, and the delay that had been occasioned in completing and sinking these eighteen cones, exhausted the patience of the Govern ment, so that, in the following year, 1789, it caused the three cones,. then on the building slips, to be sold for whatever they would fetch.