80 OBSERVATIONS ON THE STORM OF DECEMBER 15, 1839. 



the errors of observation and the deflecting influences of the great valleys and 

 lines of elevation, as well as by the errors of approximation which often arise 

 from referring all winds to eight, or, at most, to sixteen points of the compass. 



It is not intended, on this occasion, to support the foregoing characteristics 

 by such extended details of evidence as their discussion would necessarily de- 

 mand ; and they are mentioned here only because the true character of the ro- 

 tation in these gales, as well as the necessary or incidental connexion of this 

 rotation with other phenomena which attend them, has seemed to be often 

 misappreh ended , 



As relates to the whirling or rotary action in the case before us, it may be 

 remarked, that had we obtained no observations from the north-western side of 

 the axis of this gale, it would have been easy, in the absence of more strictly 

 consecutive observations than are usually attainable, to have viewed the initial 

 south-easterly wind of the gale,* and the strong north-westerly wind which 

 soon followed, as two distinct sheets, or currents of wind, blowing in strictly 

 opposing directions: and if we could so far lose sight of the conservation of 

 spaces and areas, the laws of momentum and gravitation, together with a con- 

 tinually depressed barometer within the storm, we might then have supposed 

 one of these great winds, if not both, to have been turned upward by an unseen 

 deflection, and doubled back upon itself in the higher atmosphere. But the 

 case neither calls for nor admits these speculations. If, however, the axis of 

 this gale had chanced to pass westward and northward of our limits of correct 

 observation, in pursuing its north-easterly course, as did, perhaps, that of the 

 storm of December 2Ist, 1836, which has been ably examined and discussed 

 by Professor Loomis,t it is, in such case, more than probable that its whirl- 

 wind character would not have been established. 



* Observed between the coast of Massachusetts and latitude 35° N. 

 t Trans. Am. Phil. Soc, Vol. VII., p, 125—163. 



