Besides, even if no changes were necessary, if the air-craft was always when at anchor to be arranged at one certain angle with the horizon, this very derangement of the level although constant, would be attended with all the inconvenience which I have already pointed out in considering the horizontal equilibrium of the system when floating freely in the air. M. Monge gives a very loose statement of the conditions affecting the position of the gas-vessel converted into a kite, taking no notice of the direct horizontal pressure of the wind on the bows of the gas-vessel, where but a very small fraction of the force can be resolved vertically, on account of the more unfavourable angle at which the surface is there presented to it. He leaves the question by stating that the angle at which the air-craft will have to be inclined, to enable the wind to lift it, will be very small, and will therefore cause no inconvenience to the passengers. The question is in fact one of some complexity, and depends for its solution on the form of the gas-vessel, according to the extent of under surface which it offers as available for the kite purpose, and to the extent of front which it will present in its inclined position to receive the direct drive of the wind. Further, even if such a form of gas-vessel as M. Mongè proposes and insists upon, were at all admissible, which I have shown that it is not, it would be very ineffective as a kite. For it would present below at best a cylindrical surface, and usually, according to his own impossible plan, one of sharp oval section,3 not well suited for making the most of the resistance of the air, which in this condition is the effect required. I conclude then that not even M. Mongè has offered a complete solution of this particular, of the requisites of anchorage. And if this condition were so far answered; if the air-craft could anchor in safety at any desired spot; the problem is not yet satisfied. The passengers do not want to ride safely in the air till the gale is over, they want to land. I have not met with any notice of this requisite, or with any means proposed for 26 See cap. xi., above. p. 336. fulfilling it. I have already alluded to the difficulties that will frequently attend its accomplishment in the ordinary way. We may now sum up these final requisites of the journey's end, thus :— The air-craft must be able to come to anchor in all weathers; to land and to receive cargo and passengers, and to ride securely at its moorings in calm air or in a gale of wind; without disturbance of its horizontal balance. In my next part I shall endeavour to show how these ends may be effected. See pp. 167, 168, above. CHAPTER XV. CONCLUSION-SUMMARY OF CONDITIONS. I BELIEVE that we have now arrived at a complete statement of the problem of aerial navigation; and that all the main conditions which are indispensable to its success, have been enunciated in the twelve propositions under which I have collected them. There are, of course, numerous minor requisites, which are either not peculiar to air-craft as distinct from other structures, or obvious at once on the first survey of the design. Such, for instance, are the propositions that the gas-envelope must not be liable to alteration by the action of the weather; that it must be protected as much as possible from exposure to injury by blows; that all the materials must be strong enough to do their work without breaking or giving way. To enumerate all such necessaries would be to trespass needlessly on the patience of the reader; many of them will of course be pointed out with their appropriate appliances in the succeeding pages of practical suggestions. There may, perhaps, be other requisites of detail which would not suggest themselves till one entered on the design of a complete vessel; these would at once meet with their solution from the hand of the engineer. Before proceeding to consider at length the solution of the problem, it will be convenient to recapitulate the conditions which we have ascertained. In thus preparing them for treatment, as the subjects of the following part of my book, I shall arrange them in an order different from that in which I have introduced them already. In these preliminary considerations I have followed the method which seemed to me to be the most natural, leading on from point to point, as each difficulty would be likely to present itself to the mind of a person approaching the subject from without. Having now, as it were, arrived in the middle of our ground, we can look around us and map it out in plan for the reception of such materials as we have in hand to build upon it. The most appropriate mode of handling the practical part will be to arrange the matters in the order in which they would come before us in proceeding to test our theories by building an aerial vessel. I shall place, then, first the conditions respecting the construction of the air-craft, chiefly of the gas-vessel with which some of the main difficulties are concerned. These will be followed by the conditions relating to its statical equilibrium when connected with the other parts of a navigable system: the horizontal balance receiving the first consideration, and the floating agency coming next. Finally, the dynamical requisites of the motion of the craft will claim notice: the power on which the propulsion is to depend-the keystone, as it were, without which the rest of the edifice is useless, and of which the preparation has been commonly neglected by contrivers in this art— occupying the last place. I condense each proposition into a shorter form of words, as more convenient for repetition, and yet sufficiently expressing the conclusion which was before enunciated at greater length. The following, then, are the conditions of Aerial Navigation :-- 1. The envelope must be gas-proof, light, and strong. (P. 109.) 2. The vessels must be of an elongated form-that of least resistance. (P. 97.) 3. The gas-vessel must be stiff, not bending under its load. (P. 55.) 4. The gas-vessel must be firm-not yielding to the pressure of the air. (P. 60.) 5. The envelope must be charged with the lightest gas that can be obtained. (P. 121.) 6. The vessels must be able to keep a level position when propelled through the air. (P. 51.) 7. The vessels must be floating freely. (P. 144.). able to keep a level position when 8. The vessels must be able to keep a level position when floating at anchor, and to land their passengers with safety. (P. 173.) 9. The buoyancy of the gas must exactly balance the weight of the craft. (P. 133.) 10. The craft must be able to rise and fall without waste of buoyancy or of weight. (P. 79.) 11. The craft must have means of taking purchase on the air for propulsion and direction. (P. 152.) 12. The craft must be provided with powers sufficient for its propulsion. (P. 146.) Of this zodiac of requisites, the first, the second, the sixth, and the last, are the cardinal signs, of which these are the terms: BUOYANCY, SHAPE, LEVEL, POWER; and STABILITY' is the ecliptic on which they are strung, the character that stamps them all. It may not be out of place here—before taking leave of the preliminary enunciation of the conditions of aerial navigationto state the mode in which the essentials of the art have been laid down by former writers on the subject. I have already observed that the only recent authors who have examined the question in any detail, are Mr. Monck Mason, Sir George Cayley, and M. Marcy Mongè. I shall here add the conditions as stated by these gentlemen, for the purpose of showing that I have not omitted to state any essential requisite that has before been pointed out; either by those who have despaired of success, of whose views those expressed in the 'Aeronautica' of the first of these authors may be taken as the type; or by those who, like the other two gentlemen, are full of hope for the results of experiment. According, then, to Mr. Mason: 1st. The air-craft must be provided with the means of creating a reaction in the surrounding atmosphere, equivalent to the resistance it will have to encounter.' 2 2nd. To put the machinery in motion a sufficient power is required.' 3 |