102 ANNUAL REPORT 



unusual severity in the extreme south. When we refer to the 

 records of the signal service we ascertain the causes of this un- 

 usual distribution. As stated above, certain barometric condi- 

 tions are the prelude to such storms. In this case (and this is 

 but the type of all such storms), a low pressure of unusual en- 

 ergy came within the range of observation near Los Animos, 

 Col., at 3 o'clock, p. m., Washington time, on Jan, 6, 1886, from 

 which point it moved southward into the Gulf of Mexico, where 

 it was central at 3 o'clock, p. m., of the seventh; from here it 

 was deflected to the left, being noted eight hours later over the 

 mouth of the Mississippi river, and thence it passed northeast- 

 erly, following the gulf and the Atlantic coasts, reaching the 

 mouth of the St. Lawrence at 7 A. m. of the tenth. 



An area of low barometer may be illustrated by. if not com- 

 pared to, a vigorous blaze in a burning building, which creates 

 a rarified condition of the atmosphere and a consequent rush of 

 surrounding atmosphere to fill the void. In the northwestern 

 portion of our continent, in the elevated regions of the Eocky 

 mountain chain, we have a comparatively constant high baro- 

 meter. When a low starts up, a corresponding high, from this 

 region of constant high, flows in to fill the vacuum. 



Farther north, in the arctic region, may be found as a con- 

 stant or passive element, a low temperature. Without a disturb- 

 ing cause, this condition of low temperature will hover about its 

 proper latitude. When, however, a low barometer, which is al- 

 ways accompanied by high temperature arises, a high barome- 

 ter moves into its wake, thus pruducing currents of cold air from 

 the arctic region, with a resultant lower temperature. If this 

 low barometer passes through the central or northern portions 

 of the United States it is easy to understand why it should not 

 draw a volume of cold air into the southern portion of the coun- 

 try. But when the reverse is the case, as was true of the storm 

 under consideration and especially if the low has unusual energy 

 and force, we may certainly expect the whole country to be 

 overspread by a sheet of cold. 



There are natural causes which direct and control the move- 

 ments of such storms, when once inaugurated. If not, their 

 movements would be direct and they would sweep down upon us 

 of the Central Mississippi Valley, from the north rather than from 

 the west or southwest. Hudson Bay and the lakes, to the north 

 of us, with their stored summer heat, ward off these storms, 

 pushing them, as it were, to the westward and against the 



