Page:Popular Science Monthly Volume 1.djvu/685

Rh This popular opinion of change of climate through agricultural operations is far from being restricted to America. In Western Europe there is a belief that a great amelioration has taken place in all the Baltic countries since the time of the Roman domination.

In many instances these popular impressions are contradicted by well-ascertained facts. Thus, as respects the Baltic, there are records of the time of the breaking of the ice in some of the great rivers, such as the Dwina and Neva, for several centuries. These show that, during the last 300 years, the variation amounts but to a fraction of a single day.

Such fragments as have been preserved of the observations of the first discoverers of North America—the Icelandic voyagers—have been supposed to prove a change in the climate of New England during the last 800 years, it being affirmed that the vine formerly flourished in regions where it cannot now exist. One of the first papers communicated to the American Philosophical Society, in Philadelphia, was by Dr. Williamson, offering proof that, during the previous 40 or 50 years, a very great climate change had taken place; he attributed it to cultivation. Soon afterward, Dr. Williams, of Harvard University, offered evidence that the climate of Boston had changed 10° or 12° in about 160 years. A close examination of the evidence by more recent authorities has, however, shaken these conclusions. Thus, as regards the Icelandic voyages, it is shown that the description they give of the forest-growth of New England is the same that might be given now. Humboldt, in his "Views of Nature," comes to the conclusion that there has not been any change in the climate of the United States since its first colonial settlement, and in this, Noah Webster, Forry, and other American writers agree.

It is evident, however, that in a rapidly-growing city there are several local causes which may be assigned as giving origin to an increase of temperature. The quantity of fuel burnt increases with increased population and with the number of houses, and this must exert a perceptible effect in ameliorating the rigor of winter. Moreover, on sunshiny days, the reflection and radiation of the sun's warmth from the vertical sides of the houses must tend in no inconsiderable degree to raise the temperature locally, and aid in producing a thaw. The facts observed in a city are hence not a complete guide in the discussion of general climate changes.

If our climate be gradually changing, if the heat of summer is becoming less excessive, and the cold of winter more moderate, there are impending over us modifications in our social habits, and in many of our business occupations. Not only is the settlement of this question interesting in a meteorological or scientific point of view—the sanitary, engineering, manufacturing, mercantile, and agricultural consequences are also of the utmost importance.

Impressed with these considerations, I was therefore led to extend