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.