In a balloon sufficiently perfect to retain its contents of coal-gas unaltered, in quantity or amount, for six months, an equal quantity of hydrogen could not be maintained in equal purity for six weeks.

"The supporting power being estimated at 2500 pounds, and the united weights of the party amounting only to about 1200, there was left a surplus of 1300, of which again 1200 was exhausted by ballast, arranged in bags of different sizes, with their respective weights marked upon them - by cordage, barometers, telescopes, barrels containing provision for a fortnight, water-casks, cloaks, carpet-bags, and various other indispensable matters, including a coffee-warmer, contrived for warming coffee by means of slack-lime, so as to dispense altogether with fire, if it should be judged prudent to do so. All these articles, with the exception of the ballast, and a few trifles, were suspended from the hoop overhead. The car is much smaller and lighter, in proportion, than the one appended to the model. It is formed of a light wicker, and is wonderfully strong, for so frail looking a machine. Its rim is about four feet deep. The rudder is also very much larger, in proportion, than that of the model ; and the screw is considerably smaller. The balloon is furnished besides with a grapnel, and a guide-rope ; which latter is of the most indispensable importance. A few words, in explanation, will here be necessary for such of our readers as are not conversant with the details of aerostation.

"As soon as the balloon quits the earth, it is subjected to the influence of many circumstances tending to create a difference in its weight ; augmenting or diminishing its ascending power. For example, there may be a deposition of dew upon the silk, to the extent, even, of several hundred pounds ; ballast has then to be thrown out, or the machine may descend. This ballast being discarded, and a clear sunshine evaporating the dew, and at the same time expanding the gas in the silk, the whole will again rapidly ascend. To check this ascent, the only recourse is, (or rather was, until Mr. Green's invention of the guide-rope,) the permission of the escape of gas from the valve ; but, in the loss of gas, is a proportionate general loss of ascending power ; so that, in a comparatively brief period, the best-constructed balloon must necessarily exhaust all its resources, and come to the earth. This was the great obstacle to voyages of length.

"The guide-rope remedies the difficulty in the simplest manner conceivable. It is merely a very long rope which is suffered to trail from the car, and the effect of which is to prevent the balloon from changing its level in any material degree. If, for example, there should be a deposition of moisture upon the silk, and the machine begins to descend in consequence, there will be no necessity for discharging ballast to remedy the increase of weight, for it is remedied, or counteracted, in an exactly just proportion, by the deposit on the ground of just so much of the end of the rope as is necessary. If, on the other hand, any circumstances should cause undue levity, and consequent ascent, this levity is immediately counteracted by the additional weight of rope upraised from the earth. Thus, the balloon can neither ascend or descend, except within very narrow limits, and its resources, either in gas or ballast, remain comparatively unimpaired. When passing over an expanse of water, it becomes necessary to employ small kegs of copper or wood, filled with liquid ballast of a lighter nature than water. These float, and serve all the purposes of a mere rope on land. Another most important office of the guide-rope, is to point out the direction of the balloon. The rope drags, either on land or sea, while the balloon is free ; the latter, consequently, is always in advance, when any progress whatever is made : a comparison, therefore, by means of the compass, of the relative positions of the two objects, will always indicate the course. In the same way, the angle formed by the rope with the vertical axis of the machine, indicates the velocity. When there is no angle - in other words, when the rope hangs perpendicularly, the whole apparatus is stationary ; but the larger the angle, that is to say, the farther the balloon precedes the end of the rope, the greater the velocity ; and the converse.

"As the original design was to cross the British Channel, and alight as near Paris as possible, the voyagers had taken the precaution to prepare themselves with passports directed to all parts of the Continent, specifying the nature of the expedition, as in the case of the Nassau voyage, and entitling the adventurers to exemption from the usual formalities of office : unexpected events, however, rendered these passports superfluous.

"The inflation was commenced very quietly at daybreak, on Saturday morning, the 6th instant, in the Court-Yard of Weal-Vor House, Mr. Osborne's seat, about a mile from Penstruthal, in North Wales ; and at 7 minutes past 11, every thing being ready for departure, the balloon was set free, rising gently but steadily, in a direction nearly South ; no use being made, for the first half hour, of either the screw or the rudder.

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