But a humbler though not less diligent and original thinker had been at work before him, and had already practically solved the problem of the Safety-lamp. Stephenson was, of course, well aware of the desire which prevailed in the colliery districts for the invention of a lamp which should give light enough for the miners to work by without exploding the fire-damp, and the painful incidents above described only served to quicken his eagerness to master the difficulty. For several years he had been engaged, in his own rude way, in making experiments with the fire-damp in the Killingworth mine. The pitmen used to expostulate with him on these occasions, believing the experiments to be fraught with danger. One of the sinkers, called M'Crie, observing him holding up lighted candles to the windward of the "blower" or fissure from which the inflammable gas escaped, entreated him to desist; but Stephenson's answer was, that "he was busy with a plan by which he hoped to make his experiments useful for preserving men's lives." On these occasions the miners usually got out of the way before he lit the gas. In 1815, although he was very much occupied with the business of the collieries and the improvement of his locomotive engine, he was also busily engaged in making experiments upon the inflammable gas in the Killingworth Pit. As he himself afterward related to the Committee of the House of Commons which sat on the subject of Accidents in Mines in 1835, he imagined that if he could construct a lamp with a chimney so arranged as to cause a strong current, it would not fire at the top of the chimney, as the burnt air would ascend with such a velocity as to prevent the inflammable air of the pit from descending toward the flame; and such a lamp, he thought, might be taken into a dangerous atmosphere without risk of exploding. Such was Stephenson's theory, when he proceeded to embody his idea of a miner's safety-lamp in a practical form. In the month of August, 1815, he requested his friend Nicholas Wood, the head viewer, to prepare a drawing of a lamp according to the description which he gave him. After several evenings' careful deliberations, the drawing was prepared, and it was shown to several of the head men about the works. "My first lamp," said Stephenson, describing it to the committee above referred to, "had a chimney at the top of the lamp, and a tube at the bottom to admit the atmospheric air, or fire-damp and air, to feed the burner or combustion of the lamp. I was not aware of the precise quantity required to feed the combustion; but to know what quantity was necessary, I had a slide at the bottom of the tube in my first lamp, to admit such a quantity of air as might eventually be found necessary to keep up the combustion."