It is simply astonishing to hear of people trying, year after year, to propel elongated or cigar-shaped balloons with a car underneath, and a screw-propeller, of course--an experiment which was tried, unsuccessfully, forty years ago. But this is generally the first conceived project of an aspirant for fame who commences to think on the subject, and soon fancies himself the happy possessor of the secret; yet what a very small amount of science is necessary to show its fallacy. In fact, all kinds of propositions for the propulsion of balloons have been advanced and experimented upon, but scarcely any improvements have been made since the first five years after its invention; proving, perhaps, more conclusively than anything else, that the practical propulsion of balloons is an impossibility. The most remarkable idea in this respect, was undoubtedly that of Teissol. He flattered himself to be able to train geese or other birds to pull a balloon by being hitched to it, while the conductor, in a car underneath, was to direct their movements by the aid of a long pole. Although the training of birds is not so ridiculous as it may seem, yet he found that geese, if not too tough, answer the purpose of a good roast much better. And another genius, still more unique, long before balloons were invented, conceived the idea that air, like water, must have a defined limit, and that it was possible to sail on its surface like ships on the ocean. He did not state how to get up there, but lost no time in inducing the King of Portugal to forbid everyone, under penalty of death, to use said invention. So far, no one has come in conflict with that law. Yet, although the balloon is impracticable as a means of transportation, it should by no means be discarded, for it can be made very useful for scientific and other observations, to give pleasure to thousands of people by fanciful ascensions, and not the least, to serve, as stated before, sanitary purposes, when captive and well secured. But instead of lowering and elevating it continually, as is being done at present, and which occasions danger and great loss of time and money, a contrivance should be made by which persons could safely, and without interruption, be carried up and down underneath parachutes. XI.--REASONS WHY THE PROBLEM HAS REMAINED UNSOLVED. The slow progress made, and the unsatisfactory state of the question, notwithstanding the large and universal share of attention bestowed upon the subject from earliest times, must be attributed to a variety of causes, the most prominent of which are-- "The great difficulty of the problem. "The incapacity on the one hand, or theoretical tendencies on the other, of those who have devoted themselves to its elucidation.