Bishop Wilkins, who was also a disciple of the flying system, describes a species of land-sailing vessels or chariots, which were then commonly used in China: and it is rather a curious fact that a German Count, possessing as much of modesty as the generality of foreign mechanics, has lately given to the public, as his own, an invention which has been known in Europe, and occasionally employed in Asia, for the last four hundred years. But of all the plans that have hitherto been devised, those only which have mechanic power as their basis appear to have any chance of success. This may be considered as an unerring _datum_ to guide the future experimentalist, the certainty of which is fully demonstrated by a comparison of the powers of the human frame with those of the feathered tribe: for it has been calculated by an ingenious anatomist, that the muscles which move the wings downwards in a bird in many instances, constitute not less than the sixth part of the weight of the whole body; while those of a man are not one hundredth part so large. By the use of springs, however, wound to a certain degree of tension, prior to embarking upon the intended expedition, and acting upon cranks working the wings, the same power as that possessed by the feathered race may be obtained, and the springs may be readily made to draw more than fifty times their weight. By this means a whalebone, or other light carriage, may be raised, though it would be but for a short time, as it would not be in the power of the aëronaut to wind the springs so quick as the machine would require. From this, then, it will be seen that, to produce the effect necessary for this species of navigation, it is only requisite to have a first mover, which will produce more power, in a given time, in proportion to its weight, than the animal system of muscles. High pressure steam-engines have been made to operate by expansion only, and they, it appears, might be constructed so as to be light enough for this purpose. In that case, however, it will be evident that the usual plan of a large boiler must be given up, and the principle of injecting a proper charge of water into a series of tubes, forming the cavity of the fire, must be adopted in lieu of it. The following estimate will show the probable weight of such an engine with its charge for one hour.