Instead of directing his efforts to the solids, Mr. Hewitt turned his attention to gaseous bodies, believing that an incandescent gas would prove the more nearly ideal substance for a cool light. The field of the passage of electricity through gases was by no means a virgin one, but was nevertheless relatively unexplored: and Mr. Hewitt was, therefore, for the most part obliged to depend upon his own researches and experiments. In these experiments hundreds of gases were examined, some of them giving encouraging results, but most of them presenting insurmountable difficulties. Finally mercury vapor was tried, with the result that the light just referred to was produced. The possibilities of mercury-vapor gas had long been vaguely suspected--suspected, in fact, since the early days of electrical investigation, two centuries before. The English philosopher, Francis Hauksbee, as early as 1705 had shown that light could be produced by passing air through mercury in an exhausted receiver. He had discovered that when a blast of air was driven up against the sides of the glass receiver, it appeared "all round like a body of fire, consisting of an abundance of glowing globules," and continuing until the receiver was about half full of air. Hauksbee called this his "mercurial fountain," and although he was unable to account for the production of this peculiar light, which he remarked "resembled lightning," he attributed it to the action of electricity. Between Hauksbee's "mercurial fountain" and Hewitt's mercury-vapor light, however, there is a wide gap, and, as it happened, this gap is practically unbridged by intermediate experiments, for Mr. Hewitt had never chanced to hear anything of Hauksbee's early experiments, or of any of the tentative ones of later scientists. But this, on the whole, may have been rather advantageous than otherwise, as, being ignorant, he was perhaps in a more receptive state of mind than if hampered by false or prejudicial conceptions. Be this as it may, he began experimenting with mercury confined in a glass tube from which the air had been exhausted, the mercury being vaporized either by heating, or by a current of electricity. No results of any importance came of his numerous experiments for a time, but at last he made the all-important discovery that once the high resistance of the cold mercury was overcome, a comparatively weak current would then be conducted, producing a brilliant light from the glow of the mercury vapor. Here, then, was the secret of the use of mercury vapor for lighting--a powerful current of electricity for a fraction of a second passed through the vapor to overcome the initial resistance, and then the passage of an ordinary current to produce the light.