attended by sounds not unlike the hissing of a serpent, possibly due to the rubbing together of the sand particles under the influence of the strong wind.

The Simoon, or Samiel, receives other names when it blows over different parts of the world. Over parts of Egypt it is known as the Khamsin. Like the Simoon, the Khamsin is a hot and dry wind,

that is loaded with large quantities of fine sand, and produces great sufering to people exposed to it. The Khamsin wind takes its name from a word meaning fifty, which is applied to the wind because, when it is once established, it generally continues to blow for fifty days, twentyfive of these days being before the time of the spring equinox, and the same number afterwards.

The Sirocco is another hot wind that blows from the desert of Sahara over Italy. Unlike the hot winds mentioned above, however, the Sirocco is laden with moisture which it absorbs while crossing the Mediterranean Sea. It does not, however, lose its high temperature; so that during its prevalence it causes great suffering by the enervating influence it has on the body. When the Sirocco continues for several days at a time, the suffering becomes very great. The air is heavily laden with moisture, but still retains the dust it brings from the desert. The particles of suspended dust it carries permits its temperature to become very high, temperatures of 110° in the shade being common,

If you have ever experienced that terrible feeling known as spring fever, which occurs in the early part of the spring, during times of unusual moisture and heat, you may be able to form some idea of the suffering occasioned by the prevalence of the Sirocco. I can assure you, however, that the worst attack of spring fever you have ever had cannot begin to approach in severity the debilitating effect of this hot, moist wind that blows over Italy from the desert.

The Solano is a name given to a wind similar to the Sirocco, that blows from the great desert over Spain.

There is a hot southerly wind called the Foehn, Fön, or Chinook that sometimes crosses the Alps and blows down its mountain valleys, which is regarded by some as a continuation of the Sirocco. This wind is probably due to the fact that the hot, dry winds from the desert, blowing as an upper current, are drawn into the valleys by the passage of an area of low barometer, or a cyclonic area, over the country in the neighborhood. As the rare wind from the higher regions rushes down the valley, it is condensed as it falls, owing to the pressure of the air upon it. When air is compressed, its temperature rises. Indeed, it is possible to compress air to such an extent, by the use of the compressing pump shown in Fig. 36, that a bit of tinder or other combustible material can be set on fire. When, therefore, the Foehn is drawn down the mountain valley, the condensation to which it is exposed raises its temperature, so that what was a cold wind upon the mountain top reaches the valley as an unusually warm and dry wind.

FIG. 36. COMPRESSING

PUMP

This is especially the case in Swiss valleys just before the approach of a cyclonic storm.

Although the Foehn blows with the violence of a hurricane, tears trees up by the roots, and even dislodges rocks, causing them to roll down the mountain slopes, and produces torrents that sweep over the land, yet its arrival is generally gladly welcomed by the people; for this wind is the herald of spring. Its warm air rapidly melts the great masses of ice and snow that have accumulated in the upper mountain valleys; it can do more in a single day to change the appearance of the surface than the sun can in a fortnight. Indeed, it is doubtful whether, in some of the high mountain valleys, there would be any spring at all, or that the grapes could ripen in autumn in some of the plains without the help of this wind.

During the prevalence of the Foehn it is necessary to put out all fires in the houses in the mountain valleys, since a fire started in one of the houses might result in the destruction of the entire village.

Coming now to some of the exceptionally cold winds, we will first describe the Bora, a cold, dry, strong wind that blows from the northeast over the coasts of the Adriatic and the Black Seas, sometimes lasting for several days. It takes its name from Boreas, the god of the north wind.

The Bora is greatly dreaded. During its prevalence it blows with a velocity that rivals that of most hurricanes. When it blows in winter over the sea, the spray is carried great distances inland. Clothes wet by this spray are frozen stiff on the body in a few moments, thus causing great suffering. There is also a species of fog produced by small particles of water being carried into the air from the sea by the wind blowing forcibly over the surface. This fog is known as the Fumarea or the Spalmeggio.

The Mistral is a cold wind, corresponding to the Adriatric Bora, that blows in the south of France over the Gulf of Lyons, sometimes even reaching Algiers.

Reference has been made in a previous chapter to the cold breezes that sometimes roll violently from the summit of snow-clad mountains down into the valleys. An hour or more after sunset these winds rush down the mountains with icy blast, at a speed that is sometimes fatal to travellers. Darwin gives the following description of a wind of this character that blew down the Cordillera:

"My guide was passing the Cordillera with a party in the month of May; and while in the central parts a furious gale of wind arose, so that the men could hardly cling on their mules, and stones were flying along the ground. The day was cloudless, and not a speck of snow fell, but the temperature was low. It is probable that the thermometer would not have stood very many degrees below the freezing point; but the effect on their bodies, ill-protected by clothing, must have been in proportion to the rapidity of the current of cold air. My guide's brother tried to return, but he perished, and his body was found two years afterwards, lying by the side of his mule near the road, with the bridle still in his hand. Two other men of the party lost their fingers and toes; and out of 200 mules and thirty cows, only fourteen mules escaped alive. Many years ago, the whole of a party are supposed to have perished from a similar cause, but their bodies to this day have never been discovered. The union of a cloudless sky, low temperature, and a furious gale of wind, must be, I should think, in all parts of the world, an unusual occurrence."

The Pamperos is the name given to violent winds from the west and southwest that sweep over the grassy plains, or pampas, of South America. These winds are species of exceedingly violent thunderstorms, and occur in the summer season. They begin like the thunderstorms in the United States. The squall wind brings a tremendous cloud of dust from the dry pampas, and is shortly afterwards followed by a drenching rainstorm with incessant lightning and thunder. The pamperos is greatly dreaded by the vessels in the estuary of the Rio de la Plata.

CHAPTER XVII

THE MOISTURE OF THE ATMOSPHERE

Probably most of you have heard the story of the Prince who had the good fortune to possess a very remarkable cap. When he placed this cap on his head he immediately became invisible. When he wished to be seen again he had only to remove the cap from his head. The Prince, of course, had much fun playing tricks on people, as well as in punishing those who ought to be punished for the mean things they did to others, especially when they thought they could do so safely.

The story of the Invisible Prince, like many other fairy stories, is by no means as absurd as it may appear when first heard. It is not impossible to make a thing invisible and then to cause it to reappear. I do not mean making it invisible by wrapping it up in a piece of black paper, or shutting it up in drawers or closets, or covering it with boards or opaque substances; but to make it disappear right before your eyes while you are carefully watching it, and then to cause it to reappear right in the air before you, as if it were being formed out of nothing. This would surely be a wonder of the atmosphere of a very high kind.

You have no difficulty in seeing water in a glass placed on a table in the sunlight. The tumbler is not cracked nor broken, and will not leak. Therefore, the water cannot run out, and yet, if time enough be given, it will completely disappear, just as if it no longer had an existence. You may look around for it, but it cannot be found on the sides of the tumbler, nor on the table on which it is standing. It cannot be seen in the air; it cannot be seen anywhere.