make them, are far from discouragement. They say that these difficulties are soluble. Once an airship (unlike an ocean steamer, which may meet ice-floes) is clear of the land, there is no power in the wind to upset or hurt it so long as it can ride out the gale; and such staying power is close to our grasp. There are instances of free balloons which have run unharmed for hours in a 60- or even an 80-mile wind; and the extension of this power to airships is simple and legitimate.

Airships are now made which rise at 1000 feet per minute and descend without loss of gas or ballast, which can alight where the ground is rough or rocky, or covered with crops, or in small clearings among trees, or in gorse or heather, plough-land or swamps, or during a dark night, whether attendants await them or not; and this makes them available over no small fraction of the earth's surface where aeroplanes would encounter trouble in landing; moreover they can stay out till night, when the air is generally calmest. An airship can hover at a given spot; and the man in charge can with impunity abandon all control and make such written notes or

photographs as are necessary. The range of wireless transmission from airships is immense; and, since a dirigible can maintain its level or rise when the throb of its machinery is still, it can receive wireless instructions, and, what is perhaps more important still, obtain the knowledge that its own message has been satisfactorily received, and so continue to transmit useful news. Again, no aeroplane has yet travelled so far as a balloon nor mounted so high or so quickly; nor is it equally independent of air turbulence. For sea-work the airship may yet perform useful duties, since it can come down to the waves with safety, and quit them with great ease. There does not appear to be any reason why a dozen or more of small non-rigid airships should not be packed in the hull of a suitable special ship in attendance on a fleet, and carrying with it the necessary plant for producing gas, as well as devices for mooring in the open; for sufficient experience now exists for mooring devices to be considered practicable. Having given this, which is no excessively optimistic forecast of what may be achieved with the balloon type of craft, we may turn to the other part of our subject, the rationale of practical aeroplanes.

In 1809 Sir George Cayley wrote articles on flight, indicating the use of curved aerofoils; and in 1810 the artist Walker, of Hull, published diagrams of gliding models, which do not differ much from the best model aeroplanes of to-day. There can be no question that they glided well. The difficulty was to get an adequate source of power, so that the gliding should be continued and therefore constitute 'flight.' The first to make an enginedriven aeroplane which flew was Stringfellow, in 1848. Curiosity is naturally aroused by the names of the men who first invent a device so remote from utility in their day, but it is well to remember that it is equally difficult and equally creditable to invent it again independently. This seems to have occurred over and over again with aeroplanes, since the apparatus made, having no commercial value that could be appreciated without a considerable use of the imagination, fell into oblivion as soon as the inventor passed away or lost the first fervour of his zeal.

At first, our neighbours, the French, were in the rear in regard to these inventions. No organised activity like the Aeronautical Society (founded in 1866) appears to have been afoot in France; and, though the bat-like wing structure of Ader's Avion (1890) re-appeared in Germany on Lilienthal's glider (1891), and in England in Pilcher's modification of it which he called his 'Hawk' (1895), the aerodynamic value of both the German and English machines was superior to the French one, in so far as they carried their designers most successfully, while the Avion did not. This situation has been fully, too fully, modified by the superior progress of the French in later years. Yet we are glad to look back to a brief moment in that rudimentary stage at least, when we seem to have been ahead of the French both in forming our scientific organisation and in effecting flights. The writer recalls with pleasure that in 1892-3 he was privileged to be a passenger in some flights in Hiram Maxim's steam-driven aeroplane, the like of which was certainly not available on the Continent. This was, amongst other things, a most strenuous attempt to tackle the second of the great flight problems of the day, that of propulsion. The aeroplane was capable of flying, and free to fly, but not to rise above a limited level from the ground-a pair of top rails, beneath

which the aeroplane ran, having been arranged along the course to prevent this. A fortunate accident, by which the aeroplane got away from its restraining rails, gave Maxim his early position on the list of free flyers in engine-driven aeroplanes.

But our pride in Cayley, Phillips, Stringfellow and Pilcher cannot blind us to the fact that the work of two Americans, Wilbur and Orville Wright, is the startingpoint of the modern self-propelled flying apparatus. We may, however, note with gratification that Wilbur Wright, whose death we so recently have had to deplore, quoted Lilienthal, Pilcher and Chanute as the three experimenters whose methods of gliding were of use to him. Of the three problems of flight-the building of wings, the designing of propelling machinery, and the balancing and steering-it was in the last that he treated them as his teachers; and it was from that stepping-stone that he made his great advance-wing-control for the purpose of balance.

To realise the difficulty of obtaining this balance, it is necessary to grasp the fact that the velocity of wind varies to an amazing degree. Some idea of its irregularity may be gained from the wavy lines in fig. 2, taken in March this year at 35 feet from the ground. In this the crests of the waves indicate increase of wind-speed in miles per hour, and the hollows represent partial lulls. This particular curve is interesting, both because the analysis is carried to a considerably finer degree than usual, and also because it was arranged that a pilot should fly in the wind of which this is the record. The curve shows some twenty-seven changes of wind-speed in the minute. Flyers know that the balancing lever in the pilot's hand was feeling these impulses, and beating to and fro in countering their disturbing effect. The greatest wind was measured at 30 miles per hour during the fourth minute at the level of the measuring gear 35 feet up; but from this it is not possible to know what the wind was at the higher levels, above 900 feet, where flight is more safely to be practised. Other experiments have shown that on similar days the upper wind may have had a speed of some 50 miles per hour.

The accurate analysis of wind-speeds at levels such as 1000 feet is possible in France, but not so in this country,