LOCAL CLIMATOLOGY. 81 



obstruct the sun's heat from reaching the earth. As observed elsewhere, 

 and reported in the newspapers and by personal correspondence, I find, 

 first, that in ahnost all cases, perhaps all, the wave of cold, so to call it, 

 passes from Avest to east, and the cold reaches its maximum of intensity 

 in the Mississippi valley some fifty or sixty hours before it reaches this 

 place. In case of the unusual cold term last January (Jan. 8th at 

 Geneva), the cold wave appeared on the Pacific coast seven or eight days 

 before it reached us, and I have heard of it in England some ten or 

 twelve days after it had passed our meridian. There were in this case, 

 however, some unusual breaks in the wave ; as the cold at Buffalo and 

 Rochester, for example, was not unusual, being only 3° or 4° below, 

 while it was 12° below at Geneva, and increased as it progressed east- 

 ward to 31° below at Utica. In fact it would appear as though one 

 wave, that of which we first hear as on the Pacific coast, had expended 

 itself, reaching Geneva on the night of the 4-5th, the thermometer 

 falling to 1° above on the morning of the 5th, it being on that morning 

 3° below at Rochester; and another commenced immediately, forcing 

 the thermometer to 5° below on the morning of the 7th, and to 12° 

 below on the morning of the 8th, increasing m intensity eastward. The 

 second phenomenon that I have observed is, that the crest of the wave, or 

 line of maximum cold, always passes in a curvilinear direction from 

 north to the south, inclining evermore to the west, until it is lost in the 

 tropics. One such line passed through Montreal, Rouse's Point (N. Y.), 

 Utica, Pittsburg (Pa.), Nashville (Tenn.), New Orleans, Galveston, &c. ; 

 so that the moment of greatest cold was simultaneous in all the places 

 on this line, while both to the west and to the east of them the weather 

 at that moment was warmer, being 32° at Chicago and 25° or 26° at 

 Portland (Maine) ; the cold always reaching its maximum at the time 

 when the wind had reached a point of compass somewhat north of east, 

 blowing in fact about in the line that I have indicated as that of the 

 greatest cold. 



Now I think that I can generally predict the approach of such a cold 

 term some days — two at least — before its arrival, by observations that 

 are to be made in my own observatory. And the phenomena just described 

 suggest that the balance of the winds, the polar and return currents, are 

 for some reason distui'bed ; the polar current stiffening and driving back 

 the return current until the former — the polar current — prevails, and 

 becomes so strong as to blow, finally, at the moment of the greatest 

 Cab. Nat. 11 



