In the history of aeronautics, the name of Mr. Charles Green, who first turned his attention to the art in 1821, occupies a prominent place. To him the art is indebted for the introduction of carbureted-hydrogen, or coal gas, as the means of inflating balloons. Great as was the improvement effected by the substitution of hydrogen gas for rarefied air, there are serious disadvantages connected with the use of that gas. In the first place, it is procured at vast expense; and, in the second place, it is difficult to obtain it in sufficient quantity, several days of watchful anxiety having been often expended in the vain endeavor to generate a sufficiency of the gas, which, on account of the subtilty of its particles, and its strong affinity for those of the surrounding atmosphere, continued to escape almost as fast as it was produced. Perplexed at the outset with these difficulties and inconveniencies, which had not only rendered experiments comparatively rare, but even threatened the art with premature extinction, Mr. Green conceived that if coal gas, which is much cheaper and can be generated with much greater facility than hydrogen, could be employed for the purpose of inflation, an important object would be gained. To put the truth of his theory to the test, he prepared a balloon, which he inflated with coal gas, and made a successful ascent from the Green Park, on the day of the coronation of George IV. He has subsequently made some hundreds of ascensions from the metropolis, and various other parts of the empire, with balloons so inflated; and, from the year 1821, coal gas has been very generally used in experiments of this nature. Besides its economy and easy production, it has the advantage of being more easily retained than hydrogen, which, for the reasons already given, is much more readily dissipated.