1890. J NEW YORK ACADEMY OF SCIENCES. 309 



warmer than the average at all places east of the Eocky Moun- 

 tains, except in Minnesota and the Upper Missouri Valley, and 

 much colder than the average for the month on the Pacific 

 coast ; the greatest excesses occurred in the Middle Atlantic 

 States south of New York, in the Ohio valley, lower Missis- 

 sippi valley, and the southern Rocky Mountain region. The 

 greatest departures below the average occurred in northern 

 Montana, Nevada, and eastward over the British possessions 

 and Canada. 



For the month of February we find the same excesses of tem-. 

 perature taking place east of the Rocky Mountains, and a fall- 

 ing-off of heat on the Pacific coast, also in the northern part of 

 the United States and Canada. In making a comparison of the 

 winter of 1889 and 1890, it is readily seen that the change has 

 been general and the Gulf Stream effect could be but local. 



Within the last year or two most of our storms have travelled 

 across the country north of this city, generally about latitude 

 45°, some much higher, and have followed each other in such 

 rapid succession that it was only on rare occasions that an area 

 of high pressure with a cold wave could slip down from the 

 Northwest and overspread this part of the country. During 

 the months of December, 1889, January and February, 1890, 

 but one storm centre passed south of this city, which is one 

 factor in accounting for a scarcity of cold weather ; the same 

 period embraces 28 well-defined storm centres which passed 

 north of this city, each in turn causing a steady flow of warm 

 air from the south northward over the central valleys and this 

 region. 



In former years it was also found that a majority of the 

 storms passed nortii of this city, but the interval of time be- 

 tween their passage was greater, and they were generally fol- 

 lowed by an area of high pressure that would extend over a 

 greater part of the country. 



The number of storms passing off the coast south of New 

 York averaged about one-third of the number that passed north; 

 each of these drew a cold wave directly over the city. In the 

 cold year of 1875, during the months of January, February, 

 November, and December, forty-two storms passed over the 

 country; eleven passed south of this city, and the remainder to 

 the north, — ten more to the south than for the winter of 1889 

 and 1890. During the research I found that for the past few 

 years many of our storms originated in the great interior pla- 

 teau of the Rocky Mountains ; some formed very rapidly, tak- 

 ing up a course over Colorado or Wyoming, travelling on to the 

 great lakes ; others formed very slowly, sometimes with little or 

 no energy, until the whole mountain system would be enveloped 



