TRANSACTIONS OF GALKSBURG HORTICUIiTURAL SOCIETY. 



351 



than the planets depart from their orbits. We say the course of the Mississippi and 

 Hudson is southward. Considering their windings, the whirlpools and eddies of their 

 waters, their direction is scarcely more definite than the direction of the winds. 



Monsoons. — Local disturbances there are; but these are small, almost infinitesimal, 

 when compared with the body of moving air. The equatorial calms form a broad belt 

 about 5 degrees north of the equator. Between the equatorial calms and the calms of 

 Cancer the general course of the wind is from the northeast. Between the equartorial 

 calms and the calms of Capricorn the wind blows from the southeast. Between the 

 calms of Cancer and the north polar calms the wind blows from the southwest. 

 Between the calms of Capricorn and the south polar calms the wind blows from the 

 northwest. As these various winds were considered favorable to commerce, they were 

 denominated Trade Winds. In the northern portion of the Indian Ocean, from 

 October to March, the regular trade winds prevail. From April to September, the 

 wind blows in the opposite direction, i. e., from the southwest. These winds are called 

 Monsoons, because they blow half of the year in one direction ; the other half, in the 

 opposite direction. 



Influence of the Seasons. — The influence of the seasons is no small element in 

 determining the direction of local winds. In summer the land is warmer than the 

 ocean. Hence the air rises over the land, causing the wind to blow from the sea 

 towards the land. In winter the sea is warmer than the land, thereby causing the 

 wind to blow from the land to the sea. On the Rhode Island coast the winds are con- 

 trary during different portions of the year; blowing from the northwest in winter and 

 from the southwest in summer. In the State of New York the winds blow from a point 

 from 15 to 18 degrees farther south in summer than in winter. At Washington north- 

 west winds prevail in winter; southwest in summer. In Florida the prevailing wind is 

 north in winter and south in summer. On the Pacific coast, at San Francisco, the winds 

 of winter are from the northwest, while those of summer are from the southwest. 



Rain. — The atmosphere is the great agent of rainfall. The winds, blowing from 

 sea and ocean, come dripping with moisture. Hence we see why south, southeast, 

 east and northeast winds bring rain. The atmosphere, resting on the ocean in the 

 warm region of the torrid zone, is saturated with vapor, and this is wafted northward 

 and southward, and meeting the cold currents from the poles the vapor is condensed 

 and falls in the temperate zones as rain. The great reservoir whence we obtain our 

 supply of rain isthe Southern Ocean. The Mississippi, the Hudson, the Connecticut, aie 

 abundant proofs that the rainfall in the north temperate zone is more than is actually 

 needed. The excess forms mighty rivers and is hurried back to the sea again. Whai- 

 ever cause shall lessen evaporation in the equatorial regions, whether it be sun-spots, fogs 

 or cloudiness, has a tendency to diminish the amount of rainfall in the temperate regions. 

 It may be gratuitous, but I will venture to suggest that the want of rain for the last six 

 months and the absence of prevailing and violent winds are due, in a large measure, to 

 an increase in cloudiness, fog and rainfall in the tropics. Such would be the tendency 

 according to the theory here propounded. 



Unequal Distribution. — The annual fall of rain during the course of years is the 

 same, because those causes which operate to convert water into vapor are constant and 

 persistent. Heat, which is the principal factor in the solution of this problem, is neces- 

 sarily a definite quantity in the period of years, or otherwise the earth, by its increase 

 or diminution, would "melt with fervent heat," or be congealed with polar snows. 

 During a succession of years, therefore, the amount of rainfall is the same ; but it is 

 very unequally distributed over the earth's surface. The following are some of the 

 causes of this unequal distribution : latitude, elevation, mountain ranges, course of the 

 winds. The fall of rain is greatest at the equator, and diminishes in the higher latitudes. 

 At 60 degrees it is only one-sixth of the amount at the equator. Beyond 60 degrees, 

 the rainfall is slight, owing to a deficiency of moisture in the atmosphere. According 

 to Prof. Loomis, the annual fall of rain in latitude 10 degrees is loi inches; in latitude 

 20 degrees, 90 inches; 30 degrees, 70 inches; 40 degrees, 45 inches; 50 degrees, 27 

 inches; 60 degrees, 18 inches. The number of rainy days does not correspond, in ail 

 respects, with the annual fall. The greatest number is at the equator and at 60 degrees 

 of latitude. 



