Page:Popular Science Monthly Volume 1.djvu/689

Rh they strongly confirm the conclusion arrived at in those cases. Thus the mean of the first series is substantially the same as that of the third, being 55.39 and 55.51 respectively, though there is between them an interval of seventy-three years. The mean of the second is substantially the same as that of the fourth, being 52.93 degrees and 52.48 respectively, their interval being seventy-six years; and it may be especially remarked that the mean of the fifth series is very nearly the mean of all the other four, theirs being 54.07, and its 53.34 degrees.

Thus, again, we reach the same conclusion in the case of the city of Charleston that we arrived at in the case of New York, Philadelphia, and Boston, that the winter climate has not undergone any change.

The general conclusion which this examination seems to warrant, both as regards rainfall and winter climate, is this, that there has been no change in the lapse of many years. None can be substantiated as having occurred within a century. This proves that surface changes through agriculture, drainage, etc., give rise to no appreciable meteorological effect, and that the public opinion which asserts such an influence is altogether erroneous.

Only recently have precise and correct views been entertained of the progress of atmospheric changes. It is now known that cloudy weather, or rains, or fluctuations of the barometer and of the thermometer, are not of restricted or local origin, but that they have a progress in a determinate direction, often of thousands of miles. This fact is at the basis of the duties in which the Storm-Signal Corps is so ably engaged. In many parts of the United States there are prairie or treeless regions several hundreds of square miles in extent, yet these are not rainless because they are treeless; clouds drop water upon them to the same amount that they do on the neighboring wooded regions. Considerations such as these may satisfy us that the surface modifications which the Atlantic States have undergone, since their first settlement, have produced no meteorological effect, and that the rainfall and winter probably remain the same, that they were many centuries ago.

I have restricted myself, in the foregoing climate examinations, to the winter season, and have said nothing as regards the summer. Had I done otherwise, it would have extended this report to an inconvenient length. Perhaps, however, what has here been substantiated, as to the permanency in the cold of the winter, will be held as affording strong presumptive evidence of a like permanency in the heats of summer, and that in these respects there is a mean degree which is maintained through indefinitely long periods of time.

While such is our final conclusion, we must bear in mind that these mean or average results exhibit only one phase of the problem. They do not show the fact that there are brief cycles of heat and cold, of moisture and dryness, following each other under the operation of