made to successfully fly unless made on the balloon principle, and Count Zeppelin's boat is on that principle. According to the description of Eugen Wolf, an aeronaut who took part in the ascent referred to and who published an account of the same in the November number of McClure's, 1900, it is not composed of one balloon, but of a row of them, and these are not exposed when inflated to every breeze that blows, but enclosed and combined in an enormous cylindrical shell, 420 feet in length, about 38 feet in diameter, with a volume of 14,780 cubic yards and with ends pointed like a cigar. This shell is a framework made up of aluminum trellis work, and divided into seventeen compartments, each having its own gas bag. The frame is further strengthened and the balloons stayed by a network of aluminum wire, and the entire frame covered with a soft framie fibre. Over this is placed a water-tight covering of pegamoid, and the lower part covered with light silk. An air space of two feet is left between the cover and the balloons. Beneath the balloons extends a walking bridge 226 feet long, and from this bridge is suspended two aluminum cars, at front and rear of the centre, adapted to hold all the operative machinery and the operator and other passengers.

The balloons, provided with proper valves, served to lift the structure; large four-winged screws, one on each side of the ship, their shafts mounted on a light framework extending from the body of the ship, and driven backward and forward by two light benzine engines, one on each car, constituted the propelling force. Dirigibility (steering) was provided for by an apparatus consisting of a double pair of rudders, one pair forward and one aft, reaching out like great fins, and controlled by light metal cords

from the cars. A ballast of water was carried in a compartment under each car. To give the ship an upward or a downward movement the plane on which the ship rests was provided with a weight adapted to slip back and forth on a cable underneath the balloon shell. When the weight was far aft the tip of the ship was upward and the movement was upward, when at the forward end the movement was downward, and when at the centre the ship was poised and travelled in a horizontal plane. The trip was made over the lake on a quiet evening. A distance of three and three-quarter miles, at a height of 1300 feet, was made in seventeen minutes. Evolutions from a straight course were accomplished. The ship was lowered to the lake, on which it settled easily and rode smoothly.

The other great plan of air navigation receiving the attention of scientists and aeronauts is the aeroplane system. Although the cohesive force of the air is so exceedingly small that it cannot be relied upon as a sufficient resisting medium through which propulsion may be accomplished alone by a counterresisting agent like propeller blades, yet it is known what weight the air has and it has been ascertained what expanse of a thin plane is necessary without other means to support the weight of a man in the air.

To this idea must be added the means of flight, of starting and maintaining a stable flight and of directing its course. Careful observation of the manner of the flight of large heavy birds, especially in starting, has led to some successful experiments. They do not rise at once, but require an initiative force for soaring which they obtain by running on the ground before spreading their wings. The action of

the wings in folding and unfolding for maintaining the flight and controlling its direction, is then to be noted.

It is along these lines that inventions in this system are now working. An initiative mechanism to start the ship along the earth or water, to raise it at an angle, to spread planes of sufficient extent to support the weight of the machine and its operators on the body of the air column, light engines to give the wing-planes an opening and closing action, rudders to steer by, means for maintaining equilibrium, and means when landing to float upon the water or roll upon the land, these are the principal problems that navigators of the great seas above us are now at work upon.

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CHAPTER XXX.

ILLUMINATING GAS.

"How wonderful that sunbeams absorbed by vegetation in the primordial ages of the earth and buried in its depths as vegetable fossils through immeasurable eras of time, until system upon system of slowly formed rocks have been piled above, should come forth at last, at the disenchanting touch of science, and turn the light of civilised man into day." -Prof. E. L. Youmans.

"The invention of artificial light has extended the available term of human life, by giving the night to man's use; it has, by the social intercourse it encourages, polished his manners and refined his tastes, and perhaps as much as anything else, has aided his intellectual progress."-Draper.

If one desires to know what the condition of cities, towns and peoples was before the nineteenth century had lightened and enlightened them, let him step into some poor country town in some out-of-theway region (and such may yet be found) at night, pick his way along rough pavements, and no pavements, by the light of a smoky lamp placed here and there at corners, and of weeping lamps and limp candles in the windows of shops and houses, and meet people armed with tin lanterns throwing a dubious light across the pathways. Let him be prepared to be assailed by the odours of undrained gutters, ditches, and roads called streets, and escape, if

he can, stumbling and falling into them. Let him take care also that he avoid in the darkness the drippings from the overhanging eaves or windows, and falling upon the slippery steps of the dim doorway he may be about to enter. Within, let him overlook, if he can, in the hospitable reception, the dim and smoky atmosphere, and observe that the brightest and best as well as the most cheerful illuminant flashes from the wide open fireplace. Occasionally a glowing grate might be met. The eighteenth century did have its glowing grates, and its still more glowing furnaces of coal in which the ore was melted and by the light of which the castings were made.

It is very strange that year after year for successive generations men saw the hard black coal break under the influence of heat and burst into flames which lit up every corner, without learning, beyond sundry accidents and experiments, that this gast, or geest, or spirit, or vapour, or gas, as it was variously called, could be led away from its source, ignited at a distance, and made to give light and heat at other places than just where it was generated.

Thus the good Dr. Clayton, rector of Croflon, England, in 1688, distilled gas from coal and lit and burned it, and told his learned friend, Dr. Boyle, about it, who announced it with interest to the Royal Society, and again it finds mention in the Philosophical Transactions fifty years later. Then, in 1726, Dr. Hales told how many cubic inches of gas a certain number of grains of coal would produce. Then Bishop Watson in 1750 passed some gas through water and carried it in pipes from one place to another; and then Lord Dundonald in 1786 built some ovens, distilled coal and tar, burned the gas, and got a patent. In the same year, Dr. Rickel of