On being actuated by

On being actuated by gas pressure the pressure switches automatically close the electric circuit controlled by them.

On being actuated by gas pressure the pressure switches automatically close the electric circuit controlled by them.

…the vibratory system proper (a system capable of periodically changing its characteristics under the influence of external disturbances)…

On being actuated by gas pressure the pressure switches automatically close the electric circuit controlled by them.

SUBJECT AREA: Electricity, Land transport, Railways and locomotives

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Davidson, son of an Aberdeen merchant, attended Marischal College, Aberdeen, between 1819 and 1822: his studies included mathematics, mechanics and chemistry. He subsequently joined his father's grocery business, which from time to time received enquiries for yeast: to meet these, Davidson began to manufacture yeast for sale and from that start built up a successful chemical manufacturing business with the emphasis on yeast and dyes. About 1837 he started to experiment first with electric batteries and then with motors. He invented a form of electromagnetic engine in which soft iron bars arranged on the periphery of a wooden cylinder, parallel to its axis, around which the cylinder could rotate, were attracted by fixed electromagnets. These were energized in turn by current controlled by a simple commutaring device. Electric current was produced by his batteries. His activities were brought to the attention of Michael Faraday and to the scientific world in general by a letter from Professor Forbes of King's College, Aberdeen. Davidson declined to patent his inventions, believing that all should be able freely to draw advantage from them, and in order to afford an opportunity for all interested parties to inspect them an exhibition was held at 36 Union Street, Aberdeen, in October 1840 to demonstrate his "apparatus actuated by electro-magnetic power". It included: a model locomotive carriage, large enough to carry two people, that ran on a railway; a turning lathe with tools for visitors to use; and a small printing machine. In the spring of 1842 he put on a similar exhibition in Edinburgh, this time including a sawmill. Davidson sought support from railway companies for further experiments and the construction of an electromagnetic locomotive; the Edinburgh exhibition successfully attracted the attention of the proprietors of the Edinburgh 585\& Glasgow Railway (E \& GR), whose line had been opened in February 1842. Davidson built a full-size locomotive incorporating his principle, apparently at the expense of the railway company. The locomotive weighed 7 tons: each of its two axles carried a cylinder upon which were fastened three iron bars, and four electromagnets were arranged in pairs on each side of the cylinders. The motors he used were reluctance motors, the power source being zinc-iron batteries. It was named Galvani and was demonstrated on the E \& GR that autumn, when it achieved a speed of 4 mph (6.4 km/h) while hauling a load of 6 tons over a distance of 1 1/2 miles (2.4 km); it was the first electric locomotive. Nevertheless, further support from the railway company was not forthcoming, although to some railway workers the locomotive seems to have appeared promising enough: they destroyed it in Luddite reaction. Davidson staged a further exhibition in London in 1843 without result and then, the cost of battery chemicals being high, ceased further experiments of this type. He survived long enough to see the electric railway become truly practicable in the 1880s.

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PJGR / GW

SUBJECT AREA: Land transport, Railways and locomotives, Steam and internal combustion engines

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Trevithick's father was a tin-mine manager, and Trevithick himself, after limited formal education, developed his immense engineering talent among local mining machinery and steam-engines and found employment as a mining engineer. Tall, strong and high-spirited, he was the eternal optimist.

About 1797 it occurred to him that the separate condenser patent of James Watt could be avoided by employing "strong steam", that is steam at pressures substantially greater than atmospheric, to drive steam-engines: after use, steam could be exhausted to the atmosphere and the condenser eliminated. His first winding engine on this principle came into use in 1799, and subsequently such engines were widely used. To produce high-pressure steam, a stronger boiler was needed than the boilers then in use, in which the pressure vessel was mounted upon masonry above the fire: Trevithick designed the cylindrical boiler, with furnace tube within, from which the Cornish and later the Lancashire boilers evolved.

Simultaneously he realized that high-pressure steam enabled a compact steam-engine/boiler unit to be built: typically, the Trevithick engine comprised a cylindrical boiler with return firetube, and a cylinder recessed into the boiler. No beam intervened between connecting rod and crank. A master patent was taken out.

Such an engine was well suited to driving vehicles. Trevithick built his first steam-carriage in 1801, but after a few days' use it overturned on a rough Cornish road and was damaged beyond repair by fire. Nevertheless, it had been the first self-propelled vehicle successfully to carry passengers. His second steam-carriage was driven about the streets of London in 1803, even more successfully; however, it aroused no commercial interest. Meanwhile the Coalbrookdale Company had started to build a locomotive incorporating a Trevithick engine for its tramroads, though little is known of the outcome; however, Samuel Homfray's ironworks at Penydarren, South Wales, was already building engines to Trevithick's design, and in 1804 Trevithick built one there as a locomotive for the Penydarren Tramroad. In this, and in the London steam-carriage, exhaust steam was turned up the chimney to draw the fire. On 21 February the locomotive hauled five wagons with 10 tons of iron and seventy men for 9 miles (14 km): it was the first successful railway locomotive.

Again, there was no commercial interest, although Trevithick now had nearly fifty stationary engines completed or being built to his design under licence. He experimented with one to power a barge on the Severn and used one to power a dredger on the Thames. He became Engineer to a project to drive a tunnel beneath the Thames at Rotherhithe and was only narrowly defeated, by quicksands. Trevithick then set up, in 1808, a circular tramroad track in London and upon it demonstrated to the admission-fee-paying public the locomotive Catch me who can, built to his design by John Hazledine and J.U. Rastrick.

In 1809, by which date Trevithick had sold all his interest in the steam-engine patent, he and Robert Dickinson, in partnership, obtained a patent for iron tanks to hold liquid cargo in ships, replacing the wooden casks then used, and started to manufacture them. In 1810, however, he was taken seriously ill with typhus for six months and had to return to Cornwall, and early in 1811 the partners were bankrupt; Trevithick was discharged from bankruptcy only in 1814.

In the meantime he continued as a steam engineer and produced a single-acting steam engine in which the cut-off could be varied to work the engine expansively by way of a three-way cock actuated by a cam. Then, in 1813, Trevithick was approached by a representative of a company set up to drain the rich but flooded silver-mines at Cerro de Pasco, Peru, at an altitude of 14,000 ft (4,300 m). Low-pressure steam engines, dependent largely upon atmospheric pressure, would not work at such an altitude, but Trevithick's high-pressure engines would. Nine engines and much other mining plant were built by Hazledine and Rastrick and despatched to Peru in 1814, and Trevithick himself followed two years later. However, the war of independence was taking place in Peru, then a Spanish colony, and no sooner had Trevithick, after immense difficulties, put everything in order at the mines then rebels arrived and broke up the machinery, for they saw the mines as a source of supply for the Spanish forces. It was only after innumerable further adventures, during which he encountered and was assisted financially by Robert Stephenson, that Trevithick eventually arrived home in Cornwall in 1827, penniless.

He petitioned Parliament for a grant in recognition of his improvements to steam-engines and boilers, without success. He was as inventive as ever though: he proposed a hydraulic power transmission system; he was consulted over steam engines for land drainage in Holland; and he suggested a 1,000 ft (305 m) high tower of gilded cast iron to commemorate the Reform Act of 1832. While working on steam propulsion of ships in 1833, he caught pneumonia, from which he died.

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See also: Blenkinsop, John