‘Although the summers over all this valley must be admitted to be hot, yet the exemption of the country from mountains and impediments to the free course of the winds, and the circumstance, that the greater proportion of the country has a surface bare of forests, and, probably, other unexplained atmospheric agents, concur to create, during the sultry months, almost a constant breeze. It thence happens, that the air on these wide prairies is rendered fresh, and the heats are tempered, in the same manner, as is felt on the ocean.’ The annual and mean quantity of rain that falls in the United States is much greater than in most countries of Europe, certain mountainous regions and heads of gulfs excepted. This has been ascertained by numerous and accurate observations made on different parts of the Atlantic coast. It is said, on the authority of tabular views, that, on a medium, one third less rain falls in Europe than in the United States; yet Dr. Holyoke mentions, in his memoir on the climate of the United States, twenty cities in Europe, which, at a mean of twenty years, have had one hundred and twenty days of rain; while Cambridge has had but eighty-eight days, Salem ninety-five days of rain, and Philadelphia seventy-six days, at a medium of twenty years. The mean annual quantity of rain at Philadelphia is very little more than the mean annual quantity at Glasgow for a term of thirty years preceding 1790. The above greater quantity of rain, in fewer days, in America, indicates the rain to be much heavier there than in Europe. On the other hand, it is equally well ascertained, that the evaporation of these rains proceeds much quicker in America than in Europe; and that, consequently, the air is habitually drier, and less calm, unless Charleston be taken as an exception. It has been found, that the mean annual quantity of evaporation at Cambridge, near Boston, was fifty-six inches, for a term of seven years; while in seven German and Italian cities, on a mean of twenty years, the annual evaporation was forty-nine inches, or seven of difference; although the Italian cities are in a much more favorable situation for evaporation than the vicinity of Boston, adjacent to the Atlantic ocean. The same fact of greater evaporation was also observed to take place in Upper Louisiana, and along the higher Missouri, as far as the Rocky Mountains, by Captain Lewis.