a curious, and, at the same time, a beautiful sight is had as the balloon passes through the cloud, especially if the ascension is made shortly before sunset.

The possibility of crossing the ocean with a balloon was believed in to such an extent in 1840, that a Mr. Charles Green announced his readiness to attempt to cross the Atlantic in a balloon especially built for the purpose, provided a sufficient sum could be obtained.

I regret that want of space will prevent my telling you of some of the attempts that have been made to overcome obstacles at the surface by moving through the air in balloons, especially during wars. I must, however, tell you something about Andrée.

Solomon Auguste Andrée, a Swedish aëronaut, conceived the bold idea of reaching the North Pole by the aid of a balloon. Accompanied by Dr. S. T. Strindberg and Herr Fraenckell, he left Dane's Island, on the coast of Spitzbergen, on the 11th of July, 1897.

Andrée's balloon had a capacity of 170,000 cubic feet of gas, its diameter being sixty-four and a half feet. Assuming that its speed would average from ten to twelve miles an hour, the balloon should have been able to carry these men to the pole in six days, provided, of course, the wind blew from the right direction.

Poor Andrée and his companions undoubtedly perished; for, although two days after their departure from Spitzbergen a message was received by a carrier pigeon, stating that the balloon had reached lat. 82.2° N., and long. 15.5° E., and was still making satisfactory progress, yet neither the balloon nor its occupants were ever heard from again.

During the last ten years many improvements have been made in balloons. The most important of these have been in their construction, whereby their motion through the air is to a great extent independent of the direction of the air currents in which they may be immersed. Of course, in order to do this, the balloon must be provided with motive

power that is independent of the action of the winds. This power can be obtained either by powerful electric motors, driven by electric storage batteries placed in the balloon, or by a gas engine driven by gasoline or similar material. The latter machines appear to have produced the best results, since by their use a greater amount of power can be obtained with the least weight of machinery.

Balloons that are capable of moving through the air in directions irrespective of the winds, are generally known as dirigible balloons. Some of the distinguished men who have worked in this direction are Gaston Tissandier, who was the first to partially solve this problem. At a latter date, Santos-Dumont, of Paris, constructed a dirigible balloon by which in November, 1899, he was able to circle around the great Eiffel Tower.

Inasmuch as a pear-shaped balloon possesses the disagreeable feature of spinning, or rotating like a top, different shapes have been given to balloons. Cigar-shaped balloons have been frequently employed as dirigible balloons.

CHAPTER XXIV

OPTICAL PHENOMENA OF THE ATMOSPHERE

That our atmosphere is transparent, is evident from the possibility of distinctly seeing distant objects. But the degree of this transparency differs markedly from time to time. The presence of even an exceedingly small quantity of fog particles in the air so decreases its transparency as to very greatly limit the distance at which objects are visible. In a similar manner, especially after a long dry spell in summer, the air may be so filled with minute particles of dust as to cause a haze that greatly limits our vision.

The atmosphere, together with the different objects on the earth's surface, are frequently spoken of as the "face of Nature." In this sense, Nature, like some of her children, often sadly needs to have her face washed. This is practically done whenever it rains.

You have doubtless noticed how much clearer the distant landscape is immediately after a rain, followed by clearing weather and a blue sky. This is because the rain has washed most of the dust and dirt out of the air.

The transparency of the atmosphere differs markedly with its height. If you have ever ascended a high mountain, or, indeed, for the matter of that, a fairly high hill, you may have noticed how much clearer during certain days the air seems than during other days. As you look towards a distant range of mountains, you are able to see with much greater clearness the details of different objects on its higher levels, than you can in the valley below. This is because there are fewer dust particles in the higher air than in the lower air of the valleys.

per that is in l-pendent of the action of the winds. This power can be obtained either by powerful electric motors, unen by eletne storage batteries placed in the balloon, or v a zs erzine driven by gasoline or similar material. The latter machines appear to have produced the best ree by their use a greater amount of power can be eltui ath the least weight of machinery.

Bs that are capable of moving through the air in Let s irrespective of the winds, are generally known as

ball vs. Some of the distinguished men who have ked in this direction are Gaston Tissandier, who was the first to partially solve this problem. At a latter date, SanDannt, of Paris, constructed a dirigible balloon by wh. h in November, 1899, he was able to circle around the great Efel Tower.

Inasmuch as a pear-shaped balloon possesses the disagreeal le feature of spinning, or rotating like a top, different shapes have been given to balloons. Cigar-shaped balloons have been frequently employed as dirigible balloons.

CHAPTER XXIV

OPTICAL PHENOMENA OF THE ATMOSPHERE

That our atmosphere is transparent, is evident from the possibility of distinctly seeing distant objects. But the degree of this transparency differs markedly from time to time. The presence of even an exceedingly small quantity of fog particles in the air so decreases its transparency as to very greatly limit the distance at which objects are visible. In a similar manner, especially after a long dry spell in summer, the air may be so filled with minute particles of dust as to cause a haze that greatly limits our vision.

The atmosphere, together with the different objects on the earth's surface, are frequently spoken of as the "face of Nature." In this sense, Nature, like some of her children, often sadly needs to have her face washed. This is practically done whenever it rains.

You have doubtless noticed how much landscape is immediately after a rai weather and a blue sky. This is bec most of the dust and dirt out of the The transparency of the atm with its height. If you have ever or, indeed, for t