_C._ =The Formation of Dew.=——The formation of dew is to be studied from the following points of view, viz., as dependent upon: _a_, the temperature and the humidity of the air; _b_, the exposure and condition of the ground; _c_, the state of the sky; and _d_, the movement of the air. The occurrence of dew on any night, as well as the amount, whether large or small, can readily be ascertained by inspection. Observe the conditions of temperature, humidity, cloudiness, and wind direction and velocity, as in previous exercises. Pay special attention to the state of the sky, the wind movement, and the vertical distribution of temperature near the ground. Under heading _b_ (exposure and condition of the ground) make observations of the amounts of dew formed on hilltops, hillsides, and in valleys; on different kinds of surface covering, as grass, leaves, pavements, etc., and over different kinds of soil. Classify the results in accordance with the conditions under which the observations were made. Compare the results and draw your conclusions from this study. Practise making predictions of the formation of dew in different places and under different weather conditions. Over the greater portion of the earth’s surface the amount of dew which is deposited is very small. It has been estimated that in Great Britain the total annual amount would measure only an inch and a half in depth; and in central Europe the depth is given as hardly one inch. In some parts of the Torrid Zone, on the other hand, dew is deposited in much larger quantities. According to Humboldt, the traveler through some of the South American forests often finds what seems to be a heavy shower falling under the trees, while the sky is perfectly clear overhead. In this case dew is formed on the tops of the tree in sufficiently large quantities to give a shower underneath. It is reported that on the Guinea coast of Africa the dew sometimes runs off the roofs of the huts like rain. In many dry regions the dew is an important agency in keeping the plants alive. _D._ =The Formation of Frost.=——The formation of frost is to be studied in the same way as that suggested in the case of dew, _i.e._, as dependent upon: _a_, the temperature and the humidity of the air; _b_, the exposure and condition of the ground; _c_, the state of the sky; and _d_, the movement of the air. Frosts are usually classified as _light_ or _heavy_. The words _killing frost_ are also used. Study the weather and surface conditions which are most favorable to the formation of frost. Pay special attention to the relation of frost and inversions of temperature; to the frequency of frost on open or sheltered surfaces; on hills or in valleys, and on the lower and upper branches of trees and shrubs. Determine, as well as you can, the weather conditions which precede light or heavy frosts, and make predictions of coming frosts, when the conditions warrant them.