Early Methods And Ideas.
Before proceeding to introduce the chief actors and their achievements in the period next before us, it will be instructive to glance at some of the principal ideas and methods in favour with aeronauts up to the date now reached. It will be seen that Wise in America, contrary to the practice of Green in our own country, had a strong attachment to the antique mode of inflation with hydrogen prepared by the vitriolic process; and his balloons were specially made and varnished for the use of this gas. The advantage which he thus bought at the expense of much trouble and the providing of cumbersome equipment was obvious enough, and may be well expressed by a formula which holds good to-day, namely, that whereas 1,000 cubic feet of hydrogen is capable of lifting 7 lbs., the same quantity of coal gas of ordinary quality will raise but 35 lbs. The lighter gas came into all Wise's calculations for bolder schemes. Thus, when he discusses the possibility of using a metal balloon, his figures work out as follows: If a balloon of 200 feet diameter were constructed out of copper, weighing one pound to the square foot; if, moreover, some six tons were allowed for the weight of car and fastenings, an available lifting power would remain capable of raising 45 tons to an altitude of two miles. This calculation may appear somewhat startling, yet it is not only substantially correct, but Wise entertained no doubt as to the practicability of such a machine. For its inflation he suggests inserting a muslin balloon filled with air within the copper globe, and then passing hydrogen gas between the muslin and copper surfaces, which would exclude the inner balloon as the copper one filled up.