secant een aaa 
a 
Observations on the Storm of Dec. 15, 1839. 115 
lieved to contribute largely to the clouds and rain which usually 
accompany a storm or gale ; and is probably due, in part, to the 
excess of external atmospheric pressure on the outward portions 
of the revolving storm. 
8. In storms which are greatly expanded there is sometimes 
found an extensive area of winds of little force and variable di- 
rection, lying within the circuit of the true gale, and attended 
throughout with a depressed state of the barometer. This more 
quiescent portion of air in the centre of a gale has been found to 
extend, in some cases, to a diameter of several hundred miles. 
Tn the case now before us, the direction of the arrows repre- 
senting the course of the wind at noon, as carefully drawn ona 
larger map, shows an average convergence, or inward inclination, 
of about six degrees. But it is not deemed safe to rely upon this 
result in a single case, which is liable to be affected by 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 anes extended details of evidence as their dis- 
cussion would necessarily demand ; and they are mentioned here 
only because the true character of ‘the rotation in these gales, as 
well as the necessary or i 1 connexion of this rotation 
with other phenomena which attend them, has seemed to be of- 
ten misapprehended. 
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 northwestern side of the axis of this gale, it would 
have been easy, in the absence of more strictly consecutive ob- 
servations than are usually attainable, to have viewed the initial 
southeasterly wind of the gale,* and the strong. northwesterly 
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 continually de- 
pressed barometer within the storm, we might then have suppos- 
ed one of these great winds, if not both, to have been turned 
* Observed between the coast of Massachusetts and latitude 25° N. 
