186 THE CLIMATE OF I'KIKCE GEOKGE S COVXTY 



minor degree on its topography, the slope of the surface, whether 

 valley or mountain top, the nature of the soil and soil covering, and 

 lastly, on the position of the region with reference to the prevailing- 

 path of storms. 



The sun's power is greatest when the rays strike the earth's surface 

 vertically, and the highest temperatures might be expected to occur 

 in regions where the sun is overhead at noon, which can take place 

 only within the tropics. The inclination of the earth axis 231/0 

 degrees from the perpendicular to the plane of its orbit profoundly 

 modifies this simple deduction by causing a variation in the length 

 of the day as the pole is approached. During the summer of the 

 northern hemisphere the length of the day increases rapidly from 

 the equator toward the pole, and the increased duration of sunshine 

 compensates largely for the greater inclination of the sun's rays. 

 ]\raryland, lying between the parallels of 38° and 40° north Latitude, 

 at the time of the summer solstice, June 21, has a day of nearly 15 

 hours' duration, and the soil and air are able to accumulate a large 

 store of heat during the long summer day. The long winter nights 

 which favor the loss of heat by outward radiation give a sharp con- 

 trast to the different seasons which is quite absent in polar or tropical 

 latitudes. The factors wdiich control climate act together in so 

 intricate a manner that it is difficult to ascertain precisely what 

 effect latitude itself to the exclusion of other causes may have upon 

 the climate of a region. 



The position of a cotmtry with reference to mountain chains or to 

 large bodies of water has a profound effect on climate. Over any 

 level plain, even in tropical regions, the temperature decreases in 

 free air about 1° Fahrenheit for every 300 feet increase of elevation. 

 M'ountains thrust themselves up into this region of colder air and 

 thus lower the temperature of their surroundings. Again, moun- 

 tains have a strong influence on rainfall by facilitating the ascent 

 of moist air currents flowing up their slopes, and so causing con- 

 densation and precipitation by dynamic cooling. On the other hand 

 large masses of water have a conserving influence, lessening extremes 

 of temperature, and their action is so powerful as to determine the 

 difference between what is called continental and marine climates. 



