Page:Popular Science Monthly Volume 1.djvu/682

666 For 1871 the total rainfall was 52.06 inches, distributed as follows:

So far as these years are concerned, there does not appear any evidence of a decrease; on the contrary, in the last there is a very considerable excess over either of the others.

Extending our examination to preceding years, as far bach as the beginning of 1836, and grouping those years into three periods, each of ten, and one of six years, the statement comes to this:

This would make the annual rainfall, throughout these thirty-six years, 47.62 inches. That of the last three years is 47.06 inches. These numbers being substantially the same, it may be concluded that, though there are large variations from year to year, these on the whole will neutralize one another, when very long periods of time are considered.

In the foregoing table the numbers from 1836 to 1854 inclusive are derived from the observations made by the military officers at Fort Columbus, New York Harbor; 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 rainfall at Fort Columbus, that in New York City, and that in the Central Park, are the same—an assumption which, I suppose, is 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, 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. Although in the last 38 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 forest, 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, there has been an actual increase. It appears, therefore, that the wide-spread public impression, that the clearing of Ian diminishes the volume of rain, is not founded on fact, and in truth