The rock on which the lighthouse rests consists of an extremely hard and resistant black porphyry. Nevertheless, as in some places it showed numerous fissures, the work began with the removal of all the superficial part, so as to secure a properly sound basis; and as, at the same time, it was of great importance that the foundation should never be exposed, M. Reynaud adopted the necessary measures to sink it completely in the rock. With this view, an annular surface of 38 feet in diameter, destined to support the hewn stone work, was excavated in the porphyry to a depth of about twenty inches, and dressed with the utmost exactitude; a labour of excessive difficulty on account of the tenacity of the rock, but a certain safeguard against future danger. In the groove thus protected by the whole mass of porphyry were deposited the first courses. As for the part of the rock corresponding to the interior of the tower, no special necessity for extra precautions existing in respect to it, it was left in its rough state, with simply a layer of concrete.
With a view to that stability which has become for the engineer a principle of elegance, the building, 155 feet in height, has been divided into two principal parts. The first, concave at its base, is of solid masonry up to three feet three inches above the level of the highest tides; its diameter at the base is 38 feet, and at its summit 28 feet. The second, reposing on this impregnable foundation, presents that measure of lightness which would have been considered suitable for a tower of the same elevation built upon the mainland. The thickness of the wall is 50 inches below, and 30 inches above.
As for the methods adopted by the architect, it does not seem necessary to describe them in detail; they would only prove interesting to readers of scientific acquirements. Yet we feel disinclined to pass over in silence a bold conception which does honour to M. Reynaud; namely, that, contrary to a generally accepted idea, it is not necessary in works of this kind to bind together all the stones as a whole, under a supposition that the sea may sweep them away during or after the execution of the works. Thus, in the lighthouses of the Eddystone and the Bell Rock, all the stones in the lower courses are dove-tailed into one another after the most ingenious designs, and held together by plugs of iron and wood. Unquestionably, says Reynaud, these arrangements are not without efficacy; but it is doubtful whether sufficient reasons for them exist. Perhaps they even present more inconveniencies than advantages, for, in addition to their cost, they necessitate a troublesome delay in the execution of works which it is of importance to raise as rapidly as possible above the level of the sea.
The architect of the lighthouse of the Héaux has not, then, fixed each single stone; he has confined himself to arresting at certain points the total mass of water which he supposed might be set in motion during each tide. Consequently each layer was divided, for this purpose, into a certain number of portions; twelve for the lower, and eight for the upper courses. All the stones of these great key-stones rested one upon another by means of salient and re-entering edges; and, more, those of the angles were securely fastened to the course beneath by plugs of granite. Experience has proved this simple arrangement to be sufficient; no injury has occurred to contradict the principle on which it was founded.
Such are the means by which this almost unequalled pharos of the Héaux was completed. It occupied six years in erection. The first was employed in examining the localities and perfecting the plans; the second, in the establishment of the cabins and the formation of the groove in the rock; the third, in the construction of the solid masonry; during the fourth, the tower was raised as far as the first gallery; in the fifth, a little above the cornice; finally, in 1839, the lantern was fixed and lighted. The monument bears the following inscription: “This edifice, commenced in 1836, was completed in 1839, in the reign of Louis Philippe.”
Rapid and successful as was the work, it was nevertheless marked by some accidents. At the commencement of the campaign of 1836, all the machines were in their places, and preparations were being made to lay the first stone, when the whole was swept away by an extraordinary wave. We have heard the engineer describe the cruel regret he experienced on arriving at the rock, after having been separated from it for three days by the tempest, and discovering all his works prostrated, most of his artificers wounded, the whole of them demoralized, and in the midst of the confusion the seamen, who had never been willing to believe in the feasibility of the matter, laughing aloud. He did not lose his courage, and skilfully revived the ardour of his men at the same time that he raised anew his apparatus. A “crab” was planted on the precipitous rock, at whose foot the barges brought alongside, and the materials were transported with the assistance of a railway laid down on the precipice which separated this natural landing-place from the site of the tower.
