Stephenson's inventive genius was first applied to a safety lamp for miners. The constant accidents in the pits at which he was working painfully forced the danger of naked lights on his attention. He made numerous experiments on the combustion of the escaping inflammable gases at Killingworth colliery, and eventually designed a safety lamp, by controlling the entry of the air to support combustion, and the escape of the products of combustion by the use of small tubes for the gases to pass through. On 21 Oct. 1815 the first lamp was actually tried, on 4 Nov. a second improved form, and on 30 Nov. a third still better were tested. On this last occasion he entered with his lamp with perfect safety into parts of the working which were full of gas.
Sir Humphry Davy [q. v.] had, unknown to Stephenson, been working on the same subject, and practically at the same time that Stephenson's long experiments bore fruit in his lamp, Davy brought out his well-known safety lamp. A fierce controversy raged for several years on the question to whom was due the credit of this solution of a problem fraught with life and death to so many thousands of miners. A national testimonial to Davy produced a testimonial to Stephenson, and he was presented with 1,000l. and an address (12 Jan. 1818). There can be little doubt that the two inventions were quite independent of each other, and that both men practically reached the same solution by different methods at the same time (cf. A Description of the Safety Lamp invented by George Stephenson, 1817).
Meanwhile Stephenson had turned his attention to the question of steam locomotion, with which his name is permanently associated. Steam locomotion on common roads had been an idea of William Murdock [q. v.], one of Watt's most trusty assistants, and he made a working model of a steam carriage in 1784. Richard Trevithick [q. v.] took up the question in 1802, constructing a carriage which ran in Cornwall, and was shown in London for a few days. In 1811 John Blenkinsop constructed a locomotive for hauling loaded coal wagons at a colliery near Leeds, which ran on rack-rails, but was very cumbersome and unwieldy. Mr. Blacket of Wylam colliery was very anxious to introduce steam-power on his horse tramways. He had two engines made, copies of Blenkinsop's locomotive, but they were failures; then he constructed a third, assisted in the design by William Hedley [q. v.], his viewer.
Stephenson saw these attempts at Wylam in progress; his interest, always keen in the matter of improving the steam-power in colliery working, was aroused, and he set himself to deal with this problem of coal haulage. He eventually, in 1813, brought the matter before the owners of his own colliery, and, receiving financial support from them, his first locomotive was built in the engine-shops at West Moor. It had smooth wheels, an improvement at which Hedley had already arrived by experiments very similar to Stephenson's, and a cylindrical barrel to the boiler thirty-four inches in diameter and eight feet long. It was tried on 25 July 1814, and successfully drew a load of thirty tons up an incline of 1 in 450 at four miles an hour. Stephenson soon recognised means of improving his engine, and in February 1815 he took out a patent for a greatly improved engine, with steam springs for the boiler to rest on. In this locomotive the steam-blast was used by him for the first time.
Trevithick had used the steam-blast in his road engines, but without any notion of its real importance. Davies Gilbert [q. v.], however, who saw it at work, recognised its great value, and wrote a letter to ‘Nicholson's Journal’ on the subject. William Nicholson (1753–1815) [q. v.] himself took out a patent for its use in 1806, but nothing came of it. Undoubtedly Stephenson was the first to use it practically with a full knowledge of its important influence on the working of the locomotive. Meanwhile he was making experiments on the traction of vehicles on smooth roads, and these experiments materially influenced his development of the crude locomotive of 1814 into the ‘Rocket’ of 1829. He found that a gradient of 1 in 200, common enough on roads, at once reduced the hauling power of a locomotive 50 per cent., since on a smooth, level road a tractive force of ten pounds would move a ton. Moreover, he found that the friction was practically independent of speed. He came to the decision, therefore, that steam carriages on ordinary roads were of no value, and that railways must be specially designed with the object of avoiding as much as possible changes of gradient. Cuttings, tunnels, and embankments were essential. In 1819 the proprietors of Hetton colliery laid down, under Stephenson's direction, a railroad eight miles in length. It was opened for traffic on 18 Nov. 1822. The traction was carried out partly by fixed engines, partly by locomotives.
On 19 April 1821 the project of connecting Stockton and Darlington by a tramroad was, after many years of discussion, approved by act of parliament. Stephenson offered his
