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.

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 Dr. Clayton, Dean of Kildare, Ireland, in 1688 distilled gas from coal and lit and burned it, and told his learned friend, the Hon. Robert 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

Worzburg lighted his laboratory with gas made by the dry distillation of bones; but all these were experiments. Finally, William Murdock, the owner of large workshops at Redruth, in Cornwall, a practical man and mechanic, and a keen observer, using soft coal to a large extent in his shops, tried with success in 1792 to collect the escaping gas and with it lit up the shops. Whether he continued steadily to so use the gas or only at intervals, at any rate it seems to have been experimental and failed to attract attention. It appears that he repeated the experiment at the celebrated steam engine works of Boulton and Watt at Soho, near Birmingham, in 1798, and again illuminated the works in 1802, on occasion of a peace jubilee.

In the meantime, in 1801, Le Bon, a Frenchman at Paris, had succeeded in making illuminating gas from wood, lit his house therewith, and proposed to light the whole city of Paris.

Thus it may be said that illuminating gas and the new century were born together the former preceding the latter a little and lighting the way.

Then in 1803 the English periodicals began to take the matter up and discuss the whole subject. One magazine objected to its use in houses on the ground that the curtains and furniture would be ruined by the saturation produced by the oxygen and hydrogen, and that the curtains would have to be wrung out the next morning after the illumination. There doubtless was good cause for objection to the smoky, unpleasant smelling light then produced.

In America in 1806 David Melville of Newport, Rhode Island, lighted with gas his own house and the street in front of it. In 1813 he took out a patent and lighted several factories. In 1817 his process

was applied to Beaver Tail Lighthouse on the Atlantic coast-the first use of illuminating gas in lighthouses. Coal oil and electricity have since been found better illuminants for this purpose.

Murdoch, Winser, Clegg and others continued to illuminate the public works and buildings of Eng land. Westminster Bridge and the Houses of Parliament were lighted in 1813, and the streets of London in 1815. Paris was lighted in 1820, and the largest American cities from 1816 to 1825. But it required the work of the chemists as well as the mechanics to produce the best gas. The rod of Science had touched the rock again and from the earth had sprung another servant with power to serve mankind, and waited the skilled brain and hand to direct its course.

Produced almost entirely from bituminous coal, it was found to be composed chiefly of carbon, oxygen and hydrogen; but various other gases were mixed therewith. To determine the proper proportions of these gases, to know which should be increased or wholly or partly eliminated, required the careful labours of patient chemists. They taught also how the gas should be distilled, condensed, cleaned, scrubbed, confined in retorts, and its flow measured and controlled.

Fortunately the latter part of the eighteenth century and the early part of the nineteenth had produced chemists whose investigations and discoveries paved the way for success in this revolution in the world of light. Priestley had discovered oxygen. Dalton had divided matter into atoms, and shown that in its every form, whether solid, liquid, or gaseous, these atoms had their own independent, characteristic, unalterable weight, and that gases diffused themselves in certain proportions.