Already Humphry was getting to be known as a scientific genius beyond the quiet neighborhood of Penzance. He had proposed a theory on heat and light which had attracted the attention of learned men; and at twenty-one he had discovered the peculiar properties of nitrous oxide--what we now call "laughing-gas"--though he nearly killed himself by inhaling too much of it. He had also made many experiments in galvanism, and had found silicious earth in the skin of reeds and grass. So famous indeed had he already become, that at the age of twenty-two--when most young men are only just leaving college--he was chosen lecturer on science at the great Royal Institution in London. There he amazed men by the eloquence and clearness with which he revealed the mysteries of science. He was so bright and attractive a young man, moreover, that the best London society gladly welcomed him to its drawing-rooms, and praises of him were in every mouth. His lecture-room was crowded whenever he spoke. But he was not a bit spoiled by all this flattery and homage. He worked all the harder; resolved to achieve yet greater triumphs in science than he had yet done. An opportunity soon arose to turn his knowledge and inventive powers to account in a very important way. For a long time the English public had every now and then been horrified by the terrible explosions which took place in the coal mines. These explosions resulted often in an appalling loss of human life. Their cause was the filling of the mine by a deadly gas, called "fire-damp," which, when ignited by a lighted candle or lamp, exploded with fearful violence. One day an explosion of fire-damp occurred which killed over one hundred miners on the spot. This event called universal attention to the subject, and Humphry Davy was besought to try and find some means of preventing, or at least lessening, similar calamities. He promptly undertook the task, and set about it with all his wonted energy. The problem before him was how to provide light in the mines in such a way that the miners might see to work by it, and at the same time be safe from the danger of fire-damp explosion. Many attempts had been made to achieve this, but they had all failed, Davy began his experiments. He soon made several valuable discoveries. One was that explosions of inflammable gases could not pass through long narrow metallic tubes. Another was that when he held a piece of wire gauze over a lighted candle, the flame would not pass through it. As a result of his long and patient toil Davy was able at last to construct his now famous _Safety-Lamp_, which has undoubtedly saved the lives of thousands during the period which has elapsed since it was invented. He presented a model of his new lamp to the Royal Society, in whose rooms in London it is to be seen to this day.