Page:Popular Science Monthly Volume 41.djvu/814

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attention, was confined to his favorite West Indian storms, which travel via the Gulf of Mexico. Espy reminded the public that these were not the only great storms which visit the United States.

"There are rain and snow storms," said Espy, "which from November to March, at least, travel from west to east. These storms are first heard of west of the Mississippi and sometimes as far north as Iowa; and they often travel from the Mississippi to the Connecticut in twenty-four hours." He concluded that these storms must originate in the far West, at that time only a wilderness, and so beyond the outposts of observation. Espy did not assert that these storms differed in character from the ones with which Redfield had dealt. He only reminded the world that the West Indies were not the only place where storms were generated. In so doing, he accurately pointed out the origin of a large proportion of American storms. The storms which Bedfield studied were really the least, in point of numbers, among the storms which visit the continent. But Redfield's observations were confined to the seaboard, so that he necessarily did not have his attention drawn to this second class of great storms. Like many later Eastern men, he did not realize what a prominent part the West plays in the economy of the country.

In two respects Prof. Espy became the critic of William C. Redfield. He held that the winds related to great storms blow radially to a center, either obliquely or directly. He also believed that the depression of the storm-center was caused, not by the centrifugal force generated by the motion of the winds, as Redfield was inclined to maintain, but was on account of the rarefaction of the air through the heat developed by the condensation of vapor in the form of rain or cloud. The latter theory proved of more value than the former, and will stand as one of Prof. Espy's additions to the meteorology of North America. The Western origin of many storms and the function of heat in the development of cyclones—these are the two contributions of Espy to the science of American storms.

Prof. Hare.—But Espy's eyes were not sharp enough to see all the facts about the origin and movement of our great disturbances; and so, as he made certain suggestions which added to the value of Redfield's discoveries, his own in turn received amendment. The chief of Espy's critics was that eminent American scientist, Dr. Hare, whose queries in regard to Espy's conclusions were pertinent and searching. He asked, among other things, "whether agreeably to the observations of Franklin and general experience confirming them, our storms producing northeasterly winds do not travel from southwest to northeast; whether their traveling thus does not warrant the opinion that they originate in the Gulf of Mexico: whether the observations of Redfield do