had a

been described. This captive balloon had capacity of only 5000 cubic feet, but it sufficed to lift an apparatus weighing sixteen pounds, designed by Dr. Assmann to record atmospheric pressure, as well as the temperature and relative humidity of the air. The balloon, attached to a cable 2600 feet long, was drawn down by a steam engine. It was possible in this way to have simultaneous observations at three levels, viz. near the ground, in the free air at a height of about half-a-mile, and at the highest level attained by a free balloon. But the captive balloon is often at a disadvantage, for the wind drives it down, and although the meteorograph mentioned had ingenious devices to neutralize the violent shocks caused by this and by the rebound of the balloon after the gust of wind, yet these impaired the automatic record. The height to which the balloon rose was so much diminished by the wind that instead of 2600 feet, which the balloon attained in calm weather when the cable was vertical, the average height of the twenty-four ascents was but half this, and in very windy weather the balloon could not rise at all.

To obviate these difficulties, a few years ago there was invented by two officers of the German army, Lieutenants von Siegsfeld and von Parsevai, a captive balloon capable of resisting strong winds, called, from its action as a kite, the Drachen

Ballon or kite-balloon, and which at the present time is being successfully used in the German

Army and Navy for reconnoitring in all kinds of weather. A smaller kite-balloon, of 7700 cubic

feet capacity, filled either with hydrogen or with illuminating gas, was first used to lift meteorological instruments at Strassburg in 1898, where it remained at a height of several hundred feet during twenty-four hours. As is seen from Fig. 4, the balloon is cylindrical, with hemispherical ends, and is attached to its cable like a kite, so that the wind acts to lift and not to depress it. The cylinder is divided by a diaphragm near its lower end into two chambers, the upper and larger one being filled with gas, while the lower chamber, by means of a valve opening inwards, receives the pressure of the wind which presses against the diaphragm, and preserves the sausagelike form of the balloon in spite of leakage of gas. Another wind-bag encircling the bottom of the air-chamber serves as a rudder, and lateral fins or wings give stability to the balloon about its longer axis. The instruments are placed in a basket hung far below the balloon. In cases where there is little or no wind at the ground, captive balloons can render valuable service for meteorological observations, but in all other cases kites are preferable. The reasons for this assertion will be given when we consider kites.

From what has been said it will be perceived how much the Germans did to advance scientific ballooning, yet their constant rivals, the French,

found a way to surpass them in the exploration of the atmosphere. For several years the struggle for supremacy in the attainment of the greatest heights was keen between the scientific men of both countries, but a truce was declared at Paris in 1896, and since then both nations have worked together harmoniously. The friendly meeting of French and German physicists at Strassburg in 1898 to agree upon the details of co-operation, typified the union of nations through science, and while it is true that the atmosphere has no boundaries and cannot be pre-empted, let us hope that the common aims of science will ultimately obliterate even political boundaries.

CHAPTER IV

BALLONS-SONDES FOR GREAT ALTITUDES-THE

INTERNATIONAL ASCENTS

WE have seen that the ascent of human beings to heights of six miles is attended with difficulty and danger, and even with apparatus for supplying the life-sustaining oxygen, man can hardly hope to reach much greater altitudes. Consequently, to obtain information about the atmospheric strata lying above six miles, that is to say, those facts which require to be ascertained in the medium itself, we must employ the so-called ballons-sondes, carrying self-recording instruments but no observers. This method, which was proposed in Copenhagen as long ago as 1809, was first put into execution by the French aeronauts, Hermite and Besançon, who, it may be remarked, suggested attempting to reach the North Pole by balloon some time before Andrée announced his scheme.

A balloon is the best of anemometers, since it