[92] It was evidently a practice at this period to vary the diameter of the trucks to suit the ship’s structure and the height of the gun-ports. “Be careful,” says Bourne in 1587, “that the trucks be not too high, for if the trucks be too high, then it will keep the carriage that it will not go close against the ship’s side.... And the truck being very high, it is not a small thing under a truck that will stay it, etc. etc. And also, if that the truck be too high, it will cause the piece to have the greater reverse or recoil. Therefore, the lower that the trucks be, it is the better.” Bourne also mentions, in the same book, the _Art of Shooting in Great Ordnance_, as a curious invention of a “high Dutchman” a gun mounting so devised as to allow the piece to rotate through 180° about its trunnions for loading. [93] Manwayring: _Sea-Man’s Dictionary_. [94] Oppenheim. [95] Hutchinson: _Naval Architecture_. [96] In the margin of the copy of _The Art of Gunnery_, Thos. Smith, A.D. 1600, in the library of the R.U.S.I. in Whitehall, is the following note, written in legible seventeenth-century script: “Some make a device to discharge at a distance by a long string, fixed to a device like a cock for a gun with a flint or like a musket cock with a match.” In the same work are instructions as to firing in a wind, when the train of powder might be blown from the vent before the linstock could be applied. The gunner was to form a clay rampart, a sort of tinker’s dam, on the metal of the piece on the windward side of the touch-hole. [97] On this Sir John Laughton remarked: “The exercise, so born, continued as long as the old men-of-war and the old guns--‘Ships passing on opposite tacks; three rounds of quick firing’” (_Barham Papers_, N.R. Soc.). [98] A form of sight for use with ordnance was described by Nathaniel Nye, in his _Art of Gunnery_, of 1674. It consisted of a lute-string and a movable bead, with a scale opposite the latter graduated in degrees and inches. [99] In Lloyd and Hadcock’s _Artillery_ an extract from a letter written in 1801 by Lord Nelson relative to a proposal to use gun-sights at sea is given. The letter is unfavourable to the invention on the ground that, as ships should always be at such close quarters with their enemies that missing becomes impossible, such appliances would be superfluous. But in this connection the observation is made that, with the degree of accuracy of guns up to the nineteenth century a rough “line of metal” aim was probably all that was justified, in the matter of sighting. In other words, with one element of the system (the gun) so very inaccurate, nothing was to be gained by increasing the accuracy of another element (the sight) to a disproportionate degree. With increasing accuracy of the gun, increasing accuracy of sight was called for.