During the time when Stephenson was working on his second locomotive explosions of fire-damp were unusually frequent in the coal mines of Northumberland and Durham, and for a space he turned his attention to the possibility of inventing some pattern of safety-lamp. The result was his perfection of a lamp that would furnish the miners with sufficient light and yet preclude risk of exploding fire-damp. This came to be known as the “Geordie Lamp,” to distinguish it from the “Davy Lamp” that Sir Humphrey Davy was inventing at about the same time. The lamp was used successfully by the miners at Killingworth, and was considered by many as superior to Davy’s lamp. Disputes arose as to which was invented first, and long controversies between scientific societies, most of which sided with the friends of Davy. Stephenson himself stated his claims firmly, but without rancor, and when he saw that it prevented the accidents in mines was satisfied that he had gained his object, and returned to the more absorbing subject of locomotives. He realized that the road and the rails were almost as important as the engine itself. At that time the railways were laid in the most careless fashion, little attention was paid to the rails’ proper joining, and less to the grades of the roads. Stephenson laid down new rails at Killingworth with “half-lap joints,” or extending over each other for a certain distance at the ends, instead of the “butt joints” that were formerly used. Over these both the coal-cars drawn by horses and his locomotive ran much more smoothly. To increase this smoothness of travel he added a system of spring carriage to his engine, and saved it from the jolting that had handicapped his first model. The second locomotive was proving so efficient at the Killingworth Colliery that friends of the inventor urged him to look into the possible use of steam in traveling on the common roads. To study this he made an instrument called the dynamometer, which enabled him to calculate the resistance of friction to which carriages would be exposed on railways. His experiments made him doubtful of the possibility of running such railroads, unless a great amount of very expensive tunneling and grading were first done. All this time George Stephenson continued to study with his son Robert. The boy was employed at the colliery, and was rapidly learning the business under the skilful charge of his father. Stephenson had decided however that Robert should have a better education than had been his, and in 1820 took him from his post as viewer in the West Moor Pit, and sent him to the University of Edinburgh.