statically charged by means of an electric machine. The line was kept charged normally; it was connected at either end with a Canton's pith-ball electrometer, so that, when the line was discharged suddenly by the operator at one end, the action became at once evident to the operator at the other end. In order to render the apparatus capable of transmitting different signals, two similar discs, on each of which was marked a number of words, letters, and figures, were attached to the seconds-arbors of two clocks beating dead seconds, and the discs were thus made to rotate synchronously before the operators at the two ends of the line. In front of either of these rotating discs was placed a fixed disc, perforated at one place, so that only one symbol was visible at a given time to either operator. To insure that this symbol should be the same at the same instant in both cases, a special signal (produced by means of an increased charge, which detonated a ‘gas-pistol’) was sent through the line, when the word ‘prepare’ was visible at the transmitting end, and repeated until the receiving operator signalled that he had adjusted his instrument so that the same word was simultaneously visible to him. The two dials were then known to be travelling in unison, and the transmitting operator could signal any given symbol by discharging the line when that symbol was visible on the disc at his own end of the line. Ronalds showed that on his line the time of transmission of each symbol was almost insensible (but foresaw and explained the retardation which must take place in lines of considerable electrostatic capacity, such as submarine cables). Ronalds's instrument was of real practical use, and the brilliant idea of using synchronously rotating discs, now employed in the Hughes printing apparatus, was entirely his own. The only defect in his invention was the comparative slowness with which a succession of symbols could be transmitted.
On 11 July 1816 Ronalds wrote to Lord Melville [see Dundas, Robert Saunders], then first lord of the admiralty, offering to demonstrate the practicability of his scheme. After some correspondence, Mr. (afterwards Sir) John Barrow [q. v.], secretary to the admiralty, wrote on 5 Aug. 1816 that ‘telegraphs of any kind are now [i.e. after the conclusion of the French war] totally unnecessary, and that no other than the one now in use [a semaphore telegraph] will be adopted.’ Sir John Barrow's son explained later that this now famous letter was written entirely at the suggestion of his father's superiors. Ronalds first published an account of his invention in 1823 (with a preface, in which he bids ‘a cordial adieu to electricity’), under the title ‘Descriptions of an Electric Telegraph and of some other Electrical Apparatus;’ a reprint, suggested by Mr. Latimer Clark, was published in 1871. In this pamphlet Ronalds speaks of his invention in a tone half of banter, half of prophecy. ‘In the summer of 1816,’ he writes, ‘I amused myself by wasting, I fear, a great deal of time and no small expenditure on the subject;’ but he was nevertheless confident that if his line had been five hundred miles long, instead of eight, it would have worked as well, and fully foresaw the practical revolution which the electric telegraph might effect. Of his official rebuff he writes with characteristic good nature: ‘I felt very little disappointment, and not a shadow of resentment … because every one knows that telegraphs have long been great bores at the admiralty’ (p. 24). Between 1816 and 1823 Ronalds travelled for two or three years through Europe and the East, and appears at this time to have begun collecting his large library of works on electricity and kindred subjects. In 1825 he invented and patented a perspective tracing instrument, intended to facilitate drawing from nature, which he improved about 1828, and described in a work called ‘Mechanical Perspective.’ These instruments seem to be the only ones for which he took out patents; the original instrument came into the possession of Sir C. Purcell Taylor, bart., in 1889. In 1836 he published, in collaboration with Dr. Blair, a series of sketches of the ‘Druidic Remains at Carnac,’ made with the Ronalds perspective instrument, and accompanied by written descriptions.
Early in 1843 Ronalds was made honorary director and superintendent of the Meteorological Observatory, which was then established at Kew by the British Association for the Advancement of Science. On 1 Feb. 1844 he was elected F.R.S. During his stay at Kew, Ronalds devised a system of continuous automatic registration for meteorological instruments by means of photography, and applied it to the atmospheric electrometer, the thermometer, barometer, declination-magnet, and horizontal and vertical force magnetographs. The first instrument was set regularly to work on 4 Sept. 1845. In a report read at the annual visitation of the Greenwich Observatory, on 1 June 1844, Sir George Biddell Airy (1801–1892) attributed the invention in part to Sir Charles Wheatstone (1802–1875) [q. v.]; but Ronalds asserted that the only assistance he had received was in the chemical portion of the process, and
