IN RAIN AND SNOW, IN THE UNITED STATES. 123 



On the chart, the curve of eight inches may he followed from Texas to New 

 Brunswick, Canada. 



A reference to Prof. Coffin's Wind Chart, 1 showing the average resulting yearly 

 direction of the wind, very plainly exhibits the intimate connection subsisting 

 between rain-fall and wind. On that chart, the direction and area of the trade- 

 wind are marked out as passing over the Mississippi delta from the S.E. ; after reach- 

 ing latitude 33°, the direction becomes more southerly, and further north changes 

 gradually into S. W. in Illinois ; it then turns west near the southern terminus of 

 Lake Michigan, having completely changed its character into the anti-trade. The 

 reader's attention may also be called to the S.E. winds blowing directly across the 

 gulf coast of Texas. The system of winds on the Pacific coast of the United 

 States is very imperfectly known ; it appears, however, that the coast of Oregon and 

 of Washington Territory is directly exposed to the westerly winds coming from the 

 Pacific, and producing, on the immediate sea-coast, the profuse winter rains. The 

 sudden increase in rain north of latitude 41°, from twenty to forty-four inches, 

 near the Straits of Juan de Fuca, is due to the direct impinging on the coast-range 

 of mountains, of the anti-trade, heavily charged with moisture ; this wind is 

 deflected, as well as the general line of the coast, south of latitude 40 |°, and hence 

 blows nearly parallel with the coast. In consequence of this change in direction, 

 the rains have diminished to ten Inches and less when we reach the latitude of the 

 Bay of Monterey, south of San Francisco. 



These (extra-tropical) winter rains extend along our Pacific coast as far south as 

 San Diego in striking contrast with the (intra-tropical) summer rains as experi- 

 enced in our lower latitudes on the Atlantic coast. 



The rain-charts for the extreme meteorological seasons give the hyetal curves 

 for every even inch, but in a few exceptional cases on the Pacific slope an interme- 

 diate curve of an odd inch has been introduced. 



It was not deemed of sufficient importance to construct rain-charts for the inter- 

 mediate or transition seasons of spring and autumn, since the curves for these 

 seasons must necessarily partake in a great measure of the characters of both ex- 

 tremes ; if their construction should become desirable, the material is given, ready 

 to hand, in the general table of the Kain-Fall. 



The connection of the rain-fall with the direction of the wind and the configura- 

 tion and topography of the country could be studied to better advantage if we 

 possessed reliable charts of the resultant direction of the wind for each of the 

 extreme seasons, and if a plain hypsometrical map, showing the form of the surface 

 by contour lines drawn for given and equal intervals, could be made the basis of our 

 rain-charts. The character of the surface, whether wooded, under culture, or arid, 

 should also be indicated on such a map. 



Respecting the general accuracy and reliability of the results exhibited by the 

 rain-charts, the necessary information will be found further on in the discussion of 

 the variations in the rain-fall. Here, however, we meet with a distinct hyetal 



1 Smithsonian Contributions to Knowledge. Winds of the Northern Hemisphere, by J. H. Coffin, 

 A.M. Washington, November, 1853. 



