Page:The American Cyclopædia (1879) Volume XI.djvu/460

 446 METEOROLOGY nitely established by Schouw (1832), although asserted "by Clark (1776) and Ilumboldt (1807). The variations which occur on the same paral- lel of latitude, and especially the seasonal dif- ferences between the pressures over the land and the ocean, were first elaborated by Buchan (1868). The charts VII. and VIII. are com- piled from the latest results published by Bu- chan and by the admiralty office in London, and must be considered as representing very nearly the actual distribution of barometric pressure over the globe, as reduced to a uni- form sea level. The irregular or non-periodic variations of the pressure are intimately con- nected with the disturbances or storms which sweep over the earth. (See HURRICANE, and STORMS.) The regions of greatest average irregular barometric variations coincide in general with the regions of most decided alter- nations between clear, cold, dry weather, and cloudy, warm, moist, or rainy weather. In an- alyzing this connection between pressure and weather, we will only mention the relation be- tween the barometer and the winds and rain. The general connection between the changes of pressure at any place and the winds is shown in the following table, which gives the aver- age reading of the barometer during the prev- alence of the respective winds for a few typi- cal stations in the northern hemisphere; in these cases, as for the entire globe, the pres- sure is greatest for cold or dry winds, and least for warm or moist winds, which law obtains in both the winter and summer seasons : Relation "between the Wind Direction and the Barometric Pressure. WIND DIBECT1ON. ST. PETEB8BUBG. LONDON. CABLSBTJHE. VIENNA. Winter. Summer. Winter. Summer. Winter. Summer. Winter. Summer. N.. inches. 28-111 23-188 28-290 28-311 28-189 28-129 28-055 27-944 23-111 inches. 28-023 28-086 28-065 28-028 27-982 28-003 28-039 28-036 28-023 inches. 29-974 29-972 29-885 29-746 29-724 29-849 29-962 29-977 29-974 inches. 29-997 30-040 80-057 29-982 29-852 29-799 29-862 29-946 29-997 inches. 29-781 29-786 29-721 29-698 29-644 29-637 29-651 29-708 29-781 inches. 29-782 29-781 29-695 29-626 29-626 29-622 29-642 29-703 29-732 inches. 29-488 29-455 29-466 29-412 29-331 29-171 29-272 29-362 29-433 Inches. 29-366 29-361 29-259 29-259 29-238 29-242 29-284 29-296 29-366 N.E.... E.... S.E S .... 8. W... V.... N. W N . The relation between atmospheric pressure and rainfall depends upon the direction of the ac- companying wind ; but if, as in the following table, each wind direction be treated by itself, it will be seen that during rain and snow the pressure is usually below the average for that wind, and is falling still lower for southerly winds and increasing rain, but is rising for northerly winds and clearing weather : Barometric Variations preceding and following Rain. WIND. Depression of barometer below the general aver- age for the respective winds at Berlin. Change in the barometer at Stockholm during the twen- ty-four hours. During rain. During snow. Preceding rain. During rain. inch. inch. Inch. Inch. N 0-143 0-242 + 0-037 + 0-053 N. E. .. 0-144 0-268 + 0-005 + 0-039 E 0-118 0-226 -o-ooi -0-036 8. E... . 0-109 0-203 -0-044 -0-058 S 0-109 0-202 -0-036- 0-054 8.W... . 0-087 0-174 -0-063 0-023 W N. W.. .. 0-069 0-109 0-189 0-169 + 0-012 + 0-027 + 0-020 + 0-094 N 0-148 0-242 + 0-037 + 0-015 The connection between the temperature, pres- sure, wind, and weather may be briefly indi- cated in the so-called weather rose, examples of which are presented for central Europe and for a portion of the United States in diagrams XVI. and XVII. We here terminate our presenta- tion of some of the more interesting relations between those meteorological phenomena which admit of exact observation, and which form a safe basis for further philosophical investi- gations. DEDUCTIVE METEOROLOGY. Of me- teorology as an inductive science, the preceding pages and the various articles referred to there- in may serve to give us some faint idea ; of it as a deductive science it would seem premature as yet to speak, were it not that the foundations DIAGBAU XVI. Weather Rose for Central Europe. of this new meteorology are now apparently well laid, although it must be confessed that the passage from crude observations back to the unknown laws of the invisible forces which guide these most complex operations of nature is not yet completely open to the student. The