102 EFFECTS OF FOHESTS ON MOISTURE 



shown by a synoptic table, these, on the whole, will neutralize one 

 another when very long periods of time are considered. 



" In the foregoing tables the numbers from 1836 to 1854, inclusive, 

 are derived from the observations made by the Military Officers at 

 Fort Columbus, New York Harbour ; those for the next twelve years 

 are from the records of Prof. Morris, in New York City ; and the 

 remainder are from the registers of this observatory. It is of course 

 assumed that the i-ainfall at Fort Columbus, that in New York City, 

 and that in the Central Park are the same, an assumption which is, 

 I suppose, under the circumstances, admissible. 



" The amount of rainfall not only influences in a predominant 

 manner the growth of plants, and, therefore, agricultural pursuits 

 determining the profitable cultivation of many different crops, but it 

 also exerts an influence on several manufacturing operations. If, 

 therefore, the above statement be correct, no apprehension need be 

 entertained .of a permanent disturbance in these particulars. Al- 

 though in the last thirty-six years great changes have been made in 

 all those portions of the United States intervening between the 

 Mississippi and the Atlantic Ocean, large surfaces having been cleared 

 of the primeval forests and brought under cultivation, their physical 

 character and aspect having therefore been essentially altered, no 

 corresponding diminution can nevertheless be traced in the mean 

 amount of water that has fallen. On the contrary, as seen in the table 

 given and in the synoptic chart, there has been an actual increase. It 

 appears, therefore, that the wide-spread public impression that the 

 clearing of land diminishes the volume of rain is not founded on fact, 

 and in truth this is no more than might have been expected from a 

 correct consideration of the meteorological circumstances under which 

 rain is produced. 



"It is the belief of European Meteorologists that the mean rainfall 

 on the western portion of that continent varies little, if at all, when 

 periods of many years are considered. In England there are rainfall 

 records reaching back to 1677. Since 1725 these records are un- 

 broken ; at present there are more than 1,500 rain-gauge stations in 

 that country. The Scotch observations extend to 1731, the Irish 

 to 1791. 



" A discussion of the observations made at the Royal Observatory 

 at Greenwich, in 1859, led to the conclusion that the annual fall of 

 rain, as compared with that previous to 1815, was becoming smaller; 

 but more extended observations, taken from gauges at stations widely 

 separated, led to the opposite conclusion, viz., that there was a per- 



