The _break-water_ erected by Mr. Rennie at Plymouth is, in its results, precisely what the noble author has here described. The plan of its construction is this: a mass of stone in blocks, of about three feet in diameter, is thrown promiscuously into the sea, and left to find their own base, the extremity of which is generally about seventy yards. This sea-wall has been carried about eight hundred fathoms in length, and the total expense attendant on its erection is estimated at £1,150,000. In 1766, Mr. Smeaton also applied loose stones to strengthen the middle piers of London bridge, which was the means of preserving that venerable structure from the almost certain ruin which threatened it. But the most economical sea-bank yet constructed was executed at Rye, in 1804, under the superintendence of the Rev. Daniel Pape, curate of that place. The dam or bank was formed in its lower part in two parallel ridges close to each other, like the double roof of a house, which were covered over, first with straw, and then with hazel faggots about thirteen feet long; and the whole was then pinned down with piles, which were united to each other at their heads by pieces put across the direction of the faggots. When this bank was completed, Mr. Pape formed another bank, on the top of the preceding, by filling up the interval between the two ridges, and covering the whole in the manner above described. All this was accomplished in one tide, and when completed it fully answered the purpose for which it was intended. No. XCVII. An instrument, whereby an ignorant person may take any thing in perspective, as justly, and more so than the most skilful painter can do by the eye. NOTE. Vitruvius is the first author who directly treats on this branch of the fine arts, though there can be no doubt but the ancients fully understood its most essential rules, which they must have practised at a very early period in the decoration of their theatres. Vitruvius, in the _proem_ to his seventh book, informs us, that Agatharchus of Athens noticed the subject, when preparing a tragic scene for a play exhibited by Æschylus: but the principles of the art were more distinctly taught by Democritus and Anaxagoras, the disciples of the former painter. Pietro del Borgo, early in the fourteenth century, constructed a very ingenious machine, which was afterwards employed by Albert Durer for the above purpose. It consisted of a transparent tablet, through which the object being viewed from a small aperture, the artist contrived to trace the images which the various rays of light emitted from them would make upon it.