The rate of motion which the Balloon thus equipped is capable of accomplishing varies according to the circumstances of its propulsion. When the Archimedean Screw precedes, the velocity is less than when it is made to follow, owing to the reaction of the air in the former instance against the car, the under surface of the balloon, and other obstacles, by which its progress is retarded. Again, when the cord upon which it travels is most tense and free from vibration, the rate is found to be considerably accelerated, compared with what it is when the contrary conditions prevail. But chiefly is its speed affected by the proper _ballasting_ of the machine itself, upon which, depends the friction it encounters from the cord on which it travels. Under ordinary circumstances it proceeds at a rate of about four miles an hour, but when the conditions alluded to have been most favourable, it has accomplished a velocity of not less than five; and there is no doubt that were it altogether free from restraint, as it would be in the open air, with a hand to guide it, its progress would be upwards of six miles an hour. Having now, I trust, sufficiently explained the principles exemplified in the model here described, it may be expected that I should add a few words regarding their reduction into practice upon a larger scale and in the open air, with such difficulties to contend with as may be expected to be encountered in the prosecution of such a design. In the first place, however, it will be necessary to disabuse the public mind of some very prevailing misconceptions with respect to the conditions of a Balloon exposed to the action of the winds, pursuing its course under the exercise of an inherent propulsive power. These misconceptions, which, be it observed, are more or less equally participated in by the scientific as by the ignorant, when devoid of that practical experience which is the basis of all aeronautical proficiency, are of a very vague and general character, and consequently not very easy accurately to define. In order, therefore, to make sure of meeting all the objections and removing all the doubts to which they are calculated to give rise, it will be advisable, even at the risk of a little tediousness, to separate them into distinct questions and treat them accordingly.