_C._ =The Occurrence and Characteristics of Local Winds, such as Mountain and Valley and Land and Sea Breezes.=——If the observer happens to be living in or near the mouth of a valley or on a mountain side, opportunity may be given for the observation of the local winds down the mountain sides and down the valley at night, and up the valley and the mountain sides by day, known as mountain and valley breezes. Keep a record of wind direction and velocity during the day, and especially during the morning and evening hours. Notice any marked changes in direction, and the relation of these changes to the time of day. Does the velocity of the daytime up-cast breeze show any systematic variation during the day? Study the relation of mountain and valley breezes to the general weather conditions shown on the weather maps. How are these breezes affected by season? By the presence of a cyclone over the region? Of an anticyclone? By the state of the sky? If near the seacoast (_i.e._, within 10 or 15 miles), an interesting study may be made of local land and sea breezes. The sea breeze is a wind from the ocean onshore, while the land breeze blows offshore. These breezes occur only in the warmer months. Take frequent observations during the day, as in the case of mountain and valley winds, noting especially any changes in direction and velocity, and the relation of these changes to the time of day. Study also the control exercised by the prevailing weather conditions over the occurrence and the strength of development of the land and sea breezes. This problem may be considerably extended by adding temperature observations to the simpler record of wind direction and velocity. In some of the Swiss valleys the mountain and valley breezes are such regular daily weather phenomena that it has become a weather proverb that a failure of the daily change in wind direction indicates a change of weather. Special names are often given to these breezes where they are well marked. In a part of the Tyrol sailing boats go up the lakes by day with the valley breeze, and sail back at night with the mountain breeze. It is therefore unnecessary for the boats to be rowed either way. Land and sea breezes, although an unimportant climatic feature in these northern latitudes, are often of the highest importance in the Torrid Zone. The fresh pure sea breeze from over the ocean makes it possible for Europeans to live in many tropical climates where otherwise they would not keep their health. The land breeze, on the other hand, is apt to be an unhealthy wind in the tropics, especially when it blows off of swampy land. CHAPTER XXII. HUMIDITY, DEW, AND FROST.