As far as the actual navigation of the air is concerned, balloonists have had everything to themselves until quite recently, but we find that at the present moment, experimenters are dividing their attention about equally between balloons or machines lighter than the air, and true flying machines or machines heavier than the air. In all Nature, we do not find any bird or insect that does not fly by dynamic energy alone, and I do not believe that the time is far distant when those now advocating machines lighter than the air, will join the party advocating machines heavier than the air, and, eventually, balloons will be abandoned altogether. No matter from what standpoint we examine the subject, the balloon is unsuitable for the service, and it is not susceptible of much improvement. On the other hand, the flying machine is susceptible of a good deal of improvement; there is plenty of scope for the employment of a great deal of skill, both mechanical and scientific, for a good many years to come.

I do not know that I can express myself better now than I did when I wrote an article for the Engineering Supplement of the Times, from which I quote the following:—

“The result of recent experiments must have convinced every thinking man that the day of the balloon is past. A balloon, from the very nature of things, must be extremely bulky and fragile.

“It has always appeared to the writer that it would be absolutely impossible to make a dirigible balloon that would be of any use, even in a comparatively light wind. Experiments have shown that only a few hundred feet above the surface of the earth, the air is nearly always moving at a velocity of at least 15 miles an hour, and more than two-thirds of the time at a velocity considerably greater than this. In order to give a balloon sufficient lifting power to carry two men and a powerful engine, it is necessary that it should be of enormous bulk. Considered as a whole, including men and engine, it must have a mean density less than the surrounding air, otherwise it will not rise. Therefore, not only is a very large surface exposed to the wind, but the whole thing is so extremely light and fragile as to be completely at the mercy of wind and weather. Take that triumph of engineering skill, the ‘Nulli Secundus,’ for example. The gas-bag, which was sausage-shaped and 30 feet in diameter, was a beautiful piece of workmanship, the whole thing being built up of goldbeater’s skin. The cost of this wonderful gas-bag must have been enormous. The whole construction, including the car, the system of suspension, the engine and propellers, had been well thought out and the work beautifully executed; still, under these most favourable conditions, only a slight shower of rain was sufficient to neutralise its lifting effect completely—that is, the gas-bag and the cordage about this so-called airship absorbed about 400 lbs. of water, and this was found to be more than sufficient to neutralise completely the lifting effect. A slight squall which followed entirely wrecked the whole thing, and it was ignominiously carted back to the point of departure.

“We now learn that the War Office is soon to produce another airship similar to the ‘Nulli Secundus,’ but with a much greater capacity and a stronger engine. In the newspaper accounts it is said that the gas-bag of this new balloon would be sausage-shaped and 42 feet in diameter, that it is to be provided with an engine of 100 horse-power, which it is claimed will give to this new production a speed of 40 miles an hour through the air, so that, with a wind of 20 miles an hour, it will still be able to travel by land 20 miles an hour against the wind. Probably the writer of the article did not consider the subject from a mathematical point of view. As the mathematical equation is an extremely simple one, it is easily presented so as to be understood by any one having the least smattering of mathematical or engineering knowledge. The cylindrical portion of the gas-bag is to be 42 feet in diameter; the area of the cross-section would therefore be 1,385 feet. If we take a disc 42 feet in diameter and erect it high in the air above a level plain, and allow a wind of 40 miles an hour, which is the proposed speed of the balloon, to blow against it, we should find that the air pressure would be 11,083 lbs.—that is, a wind blowing at a velocity of 40 miles an hour would produce a pressure of 8 lbs. to every square foot of the disc.[3] Conversely, if the air were stationary, it would require a push of 11,083 lbs. to drive this disc through the air at the rate of 40 miles an hour.

“A speed of 40 miles an hour is at the rate of 3,520 feet in a minute of time. We therefore have two factors—the pounds of resistance encountered, and the distance through which the disc travels in one minute of time. By multiplying the total pounds of pressure on the complete disc by the number of feet it has to travel in one minute of time, we have the total number of foot-pounds required in a minute of time to drive a disc 42 feet in diameter through the air at a speed of 40 miles an hour. Dividing the product by the conventional horse-power 33,000, we shall have 1,181 horse-power as the energy required to propel the disc through the air. However, the end of the gas-bag is not a flat disc, but a hemisphere, and the resistance to drive a hemisphere through the air is much less than it would be with a normal plane or flat disc. In the ‘Nulli Secundus’ we may take the coefficient of resistance of the machine, considered as a whole, as 0·20—that is, that the resistance will be one-fifth as much as that of a flat disc. This, of course, includes not only the resistance of the balloon itself, but also that of the cordage, the car, the engine, and the men.

“Multiplying 1,181 by the coefficient ·20, we shall have 236; therefore, if the new balloon were attached to a long steel wire and drawn by a locomotive through the air, the amount of work or energy required would be 236 horse-power—that is, if the gas-bag would stand being driven through the air at the rate of 40 miles an hour, which is extremely doubtful. Under these conditions, the driving wheels of the locomotive would not slip, and therefore no waste of power would result, but in the dirigible balloon we have a totally different state of affairs. The propelling screws are very small in proportion to the airship, and their slip is fully 50 per cent.—that is, in order to drive the ship at the rate of 40 miles an hour, the screws would have to travel at least 80 miles an hour. Therefore, while 236 horse-power was imparted to the ship in driving it forward, an equal amount would have to be lost in slip, or, in other words, in driving the air rearwards. It would, therefore, require 472 horse-power instead of 100 to drive the proposed new balloon through the air at the rate of 40 miles an hour.

“It will be seen from this calculation that the new airship will still be at the mercy of the wind and weather. Those who pin their faith on the balloon as the only means of navigating the air may dispute my figures. However, all the factors in the equation are extremely simple and well known, and no one can dispute any of them except the assumed coefficient of resistance, which is given here as ·20. The writer feels quite sure that, after careful experiments are made, it will be found that this coefficient is nearer ·40 than ·20, especially so at high speeds when the air pressure deforms the gas-bag. Only a slight bagging in the front end of the balloon would run the coefficient up to fully ·50, and perhaps even more.”—Times, Feb. 26, 1908.

Since writing the Times article, a considerable degree of success has been attained by Count Zeppelin. According to newspaper accounts, his machine has a diameter of about 40 feet, and a length of no less than 400 feet. It appears that this balloon consists of a very light aluminium envelope, which is used in order to produce a smooth and even surface, give rigidity, and take the place of the network employed in ordinary balloons. It seems that the gas is carried in a large number of bags fitted in the interior of this aluminium envelope. However, by getting a firm and smooth exterior and by making his apparatus of very great length as relates to its diameter, he has obtained a lower coefficient of resistance than has ever been obtained before, and as his balloon is of great volume, he is able to carry powerful motors and use screw propellers of large diameter. It appears that he has made a circuit of considerable distance, and returned to the point of departure without any accident. A great deal of credit is, therefore, due to him. His two first balloons came to grief very quickly; he was not discouraged, but stuck to the job with true Teutonic grit, and has perhaps attained a higher degree of success than has ever been attained with a balloon. However, some claim that the French Government balloon, “La Patrie” is superior to the Zeppelin balloon at all points. When we take into consideration the fact that the Zeppelin machine is 400 feet long and lighter than the same volume of air, it becomes only too obvious that such a bulky and extremely delicate and fragile affair will easily be destroyed. Of course ascensions will only be made in very favourable weather, but squalls and sudden gusts of wind are liable to occur. It is always possible to start out in fine weather if one waits long enough, but if a flight of 24 hours or even 12 hours is to be attempted, the wind may be blowing very briskly when we return, and an ordinary wind will not only prevent the housing of Count Zeppelin’s balloon, but will be extremely liable to reduce it to a complete wreck in a few minutes.[4]

I am still strongly of the opinion that the ultimate mastery of the air must be accomplished by machines heavier than the air.