Not only do mountains thus determine the absolute quantity of rain, they also affect the number of rainy days in a year. The occurrence of a rainy season depends on the amount of moisture existing in the air; and hence its frequency is greater at the Atlantic sea-board than in the interior, where the wind arrives in a drier state, much of its moisture having been precipitated by the mountains forcing it to a great elevation. Thus, on the eastern coast of Ireland it rains 208 days in a year; in England, about 150; at Kazan, 90; and in Siberia only 60 days. [Sidenote: and of snowy days.] When the atmospheric temperature is sufficiently low, the condensed water descends under the form of snow. In general, the annual depth of snow and the number of snowy days increase toward the north. In Rome the snowy days are 1-1/2; in Venice, 5-1/2; in Paris, 12; in St. Petersburgh, 171. Whatever causes interfere with the distribution of heat must influence the precipitation of snow; among such are the Gulf Stream and local altitude. Hence, on the coast of Portugal, snow is of infrequent occurrence; in Lisbon it never snowed from 1806 to 1811. Such facts teach us how many meteorological contrasts Europe presents, how many climates it contains. Necessarily it is full of modified men. [Sidenote: Vibrations of the isothermal lines.] If we examine the maps of monthly isothermals, we observe how strikingly those lines change, becoming convex to the north as summer approaches, and concave as winter. They by no means observe a parallelism to the mean, but change their flexures, assuming new sinuosities. In their absolute transfer they move with a variable velocity, and through spaces far from insignificant. The line of 50° F., which in January passes through Lisbon and the south of the Morea, in July has travelled to the north shore of Lapland, and incloses the White Sea. As in some grand musical instrument, the strings of which vibrate, the isothermal lines of Europe and Asia beat to and fro, but it takes a year for them to accomplish one pulsation. [Sidenote: Europe is full of meteorological contrasts, and therefore of modified men.]