Advancing to the place of danger, and entering within the fouled air, his lighted lamp in hand, Stephenson held it firmly out, in the full current of the blower, and within a few inches of its mouth. Thus exposed, the flame of the lamp at first increased, then flickered, and then went out; but there was no explosion of the gas. Returning to his companions, who were still at a distance, he told them what had occurred. Having now acquired somewhat more confidence, they advanced with him to a point from which they could observe the experiment repeated, but still at a safe distance. They saw that when the lighted lamp was held within the explosive mixture, there was a great flame; the lamp was almost full of fire; and then it seemed to be smothered out. Again returning to his companions, he relighted the lamp, and repeated the experiment. This was done several times, with the same result. At length Wood and Moodie ventured to advance close to the fouled part of the pit; and, in making some of the later trials, Mr. Wood himself held up the lighted lamp to the blower.[44] Such was the result of the first experiments with the _first practical Miner's Safety-lamp_, and such was the daring resolution of its inventor in testing its qualities. Before leaving the pit, Stephenson expressed his opinion that, by an alteration of the lamp which he contemplated, he could make it burn better. This was by a change in the slide through which the air was admitted into the lower part of the lamp, under the flame. After making some experiments on the air collected at the blower, by means of bladders which were mounted with tubes of various diameters, he satisfied himself that, when the tube was reduced to a certain diameter, the explosion would not pass through; and he fashioned his slide accordingly, reducing the diameter of the tube until he conceived it was quite safe. In about a fortnight the experiments were repeated in the pit, in a place purposely made foul as before. On this occasion a larger number of persons ventured to witness the experiments, which again proved successful. The lamp was not yet, however, so efficient as the inventor desired. It required, he observed, to be kept very steady when burning in the inflammable gas, otherwise it was liable to go out, in consequence, as he imagined, of the contact of the burnt air (as he then called it), or azotic gas, which lodged round the exterior of the flame. If the lamp was moved backward and forward, the azote came in contact with the flame and extinguished it. "It struck me," said he, "that if I put more tubes in, I should discharge the poisonous matter that hung round the flame by admitting the air to its exterior part."