1773–4 contains the entry ‘Millar Patrick, Banker, James's Court.’ In 1767 he was elected a director of the Bank of Scotland, and in 1790 he became deputy-governor, which office he held until his death. He is said to have rendered valuable service by organising a new system of exchanges on London. He seems to have been a man of active mind, much given to experimenting.
According to James Nasmyth (Autobiography, p. 27), Miller was one of the largest shareholders in the Carron Iron Company, and he seems to have taken part in the experiments made there for improving the construction of ordnance. It is frequently stated that he was the inventor of the carronade, so called from the Carron foundry, where they were first cast. But Miller himself never made any claim to the invention, which seems to have been due to General Robert Melville [q. v.] Anderson (op. cit.) states that Miller was so much interested in the matter that he fitted out a privateer, the Spitfire, armed with sixteen 18-pounder carronades, but there is no evidence of this, though he may have had a share in the ship. The Spitfire was captured by the Surveillante, and taken into L'Orient 19 April 1779 (see Edinburgh Advertiser, May 1779, pp. 313, 317, 340). It is probable that in this engagement carronades were first used in actual warfare [see Melville, Robert, 1723–1809]; the admiralty minute recommending their use in the royal navy was not issued until 16 July 1779.
In 1785 Miller purchased the estate of Dalswinton, Dumfriesshire, in ancient times the seat of the Comyns. He gives an account of the estate, which was in a very bad condition, in Singer's ‘Agriculture of Dumfriesshire,’ 1812, pp. 549–54. He seems to have gradually retired from active business in Edinburgh, and to have made Dalswinton his home, devoting himself mainly to schemes of agricultural improvement.
He spent much time and money in shipbuilding experiments, his main idea being the construction of ships with two or three hulls, propelled by paddle-wheels placed between the hulls and worked by men from capstans on deck. In January 1786 the Edinburgh, a triple ship upon this plan, was commenced at Leith, and was launched in October of the same year. He published a description of this vessel at Edinburgh in February 1787 in a folio tract entitled ‘The Elevation, Section, Plan, and Views of a Triple Vessel with Wheels, with Explanations of the Figures in the Engravings, and a Short Account of the Properties and Advantages of the Invention,’ copies of which were sent to all the foreign governments and to the principal public libraries. The Leith Trinity House conferred upon him the freedom of the corporation for this publication in June 1787 (Scots Mag. xlix. 309). It has now become rare, but it is reprinted in full in Woodcroft's ‘Steam Navigation,’ 1848, pp. 21, &c. The drawings were made by Alexander Nasmyth the artist, who was an intimate friend of Miller. On 2 June 1787 he made some experiments on the Firth of Forth with a double vessel, sixty feet long and fourteen and a half feet broad. Another boat of the same kind, said to have cost 3,000l., was launched at Leith in the following year (Scots. Mag. August 1788, p. 412). The ‘Gentleman's Magazine’ for December 1788, pt. ii. p. 1069, contains an engraving of the boat from a sketch taken while it was lying in Leith harbour, and Woodcroft (op. cit. p. 32) reproduces a drawing made for Miller by Alexander Nasmyth. A model of a double boat made under Miller's directions is preserved in the machinery and inventions department at South Kensington Museum. It appears from Macpherson's ‘Annals of Commerce,’ iv. 178, that one of these double ships was sent to St. Petersburg, but the frame was so much strained during the voyage that no one cared to venture home in her, and she was accordingly left in Russia.
In his description of his ‘triple vessel,’ published in 1787, Miller wrote: ‘I have reason to believe that the power of the steam engine may be applied to work the wheels. … In the course of this summer I intend to make the experiment, and the result, if favourable, shall be communicated to the public.’ Accordingly the application of the steam engine as a means of propelling boats subsequently engaged his attention, and on 14 Oct. 1788 he made his celebrated experiment on the lake at Dalswinton House with a double boat, twenty-five feet long and seven feet broad, fitted with a steam engine made by Symington. An extraordinary amount of interest has centred round this trip, which demonstrated for the first time the practicability of steam navigation. James Nasmyth (Autobiography, p. 29) says that the boat was made of tinned iron plates. He also states that Robert Burns the poet, then a tenant of Miller's, formed one of the party on board, and that the experiment was witnessed from the shore by Henry Brougham, afterwards Lord Brougham, who was on a visit to Dalswinton House. The presence of Burns has been questioned, and Brougham, in a letter printed in ‘Notes and Queries’ (5th ser. v. 247), states that he did not visit Dalswinton until many years afterwards.
