The model gun was of brass, resting on a railway formed of two inclined bars of iron, up which the recoil propelled it into a convenient position for cleaning and loading. Its own gravity caused it to fall into the required place for being again fired. The slides also served as friction-bars to regulate the recoil. The gun and the slides carrying it were enclosed in a wrought-iron box, having openings in the front and rear for the passage of the muzzle and the breech. The muzzle front of the box was pivoted to the deck by a strong bolt as a centre of motion, whilst its rear was supported on two small wheels resting on the deck, allowing the gun to change its line of horizontal fire by sweeping from the centre pivot. The gunner's seat moved with the carriage, from which he could elevate or depress the muzzle by a lever. The gun was self-priming and self-cocking; the powder charge was enclosed in a copper case. Captain Moncrieff's patent gun-carriage of the present day is described in words somewhat like those used by Trevithick forty years before. "The recoil lifted a weight smoothly and without friction; the gun and the weight were held in the position arrived at by a catch until the gun was loaded and ready to fire again."[137] [Footnote 137: See 'The Times,' August 12th, 1870.] The iron boat mentioned in his note to Lord Cochrane as being made at Hayle, was "for the purpose of sending to London to show the method of constructing ships on this plan, roomy, strong, and cheap," and was thus spoken of in a newspaper of the 26th April, 1829. "The 'Scotsman' alludes to the intended construction of iron steamboats at Glasgow by Mr. Neilson:--"For fear of the public being misled on this subject, we beg to state that so far back as last Christmas twelvemonths we saw Trevithick, of Cornwall, superintending the construction of an iron man-of-war launch, with the avowed intention of applying a similar principle of construction to the building of fast-sailing iron steamboats." This intimation, in 1829, to the since famous Glasgow iron-ship builders, that they could not claim the invention because Trevithick had made such a boat in 1827, was probably in ignorance of Trevithick's patent and models of 1809,[138] explaining the advantages of ships of iron, either under sail or under steam, for commerce or for fighting-ships. The improved high-pressure steam-engine then in hand for iron ships was but the perfecting of his plans of twenty years before.[139] [Footnote 138: See vol. i., p. 302.] [Footnote 139: See vol. i., p. 329.] "LAUDERDALE HOUSE, HIGHGATE, _April 19th, 1830_. "MR. GILBERT,