These storms are met with in their greatest severity in Egypt and Arabia. In Egypt, this wind is called the _Khamsin_, or fifty, referring to the period of fifty days--the latter part of April, May, and early June--when they may be expected. They never blow through the entire season: rarely so long as fifteen days at a time. In Arabia the simoom may travel from the center of the peninsula toward any point of the compass; the Khamsin of Egypt blows from the southwest. Winds of the same character cross the Mediterranean. In Spain the wind is known as the _Solano_, or _Levanter_, or _Leveche_: in Sicily and Italy it is the _Sirocco_. The distressing dryness is somewhat modified by the journey across the Mediterranean. The same wind in Syria is called _Samiel_; and a similar wind which blows from the Sahara southwest to the Guinea coast is called the _Harmattan_. In California a similar dry hot wind blows from the interior toward the coast, during the hot season, and is called the desert wind. Such occasional hot blasts are experienced in southeastern Dakota, coming from the “bad lands,” or sandy and rocky wastes along the upper Missouri river. All these periodical or varying winds may be very properly, from their time and character, be called the season winds of the earth, as another means of distinction from the constant trades: as they in part bring changes of season, and in part are brought that way. Into the question of climate and seasons one other element enters, of especial importance in regard to those disturbances of the regular winds, which we call storms. That factor is the quantity of moisture in the atmosphere, and the consequent rainfall or snowfall of a region. Without this element, the phenomenal disturbances known as tornadoes would hardly occur: or if they did, there would be greater difficulty in ascertaining their approach. Water, in its vapor state, is but three-fifths the weight of the air, and in consequence rapidly rises. This evaporation, as it is called, goes on at all times: even when the water is frozen. A very thin sheet of ice, hung in the open air, will finally disappear, even though the temperature be always below freezing. Now, all the phenomena of rain, snow, and hail, that are brought by different seasons, in different climes, depend upon a single simple law: that warm air can hold a much greater quantity of vapor than cold air. The amount of moisture that may be held in suspension at different temperatures is as follows: Temperature Weight of vapor Temperature Weight of vapor of Air. in a cubic foot of Air. in a cubic foot of saturated air. of saturated air.