231 J. P. Hall— Short Cycle in Weather ■. 



pressure area overlying Utah, Idaho and Oregon on the 7th is 

 associated with the cold wave (B) felt at Salt Lake City on that 

 day, at St. Paul and St. Louis on Aug. 12, and JSTew York 

 Aug. 13-15 ; its effect being increased somewhat east of the 

 Mississippi by another high pressure area from British Amer- 

 ica, which merged with the first one on Aug. 10-11. By the 

 time that the warm wave A had reached St. Paul the cold wave 

 B was affecting Salt Lake City ; so that here, as in many other 

 instances, the curve for the former station reverses that for the 

 latter. But the reversal is only apparent. Upon making the 

 proper time allowance, the parallel is found to be very close ; 

 and, with easily explicable exceptions, it holds good the year 

 round. When, however, any low or high area changes its size 

 or shape materially, or follows such a route as not to present in 

 an equally advantageous way its warm or cold winds, to a series 

 of stations, the parallel fails ; or if it exists, is accidental, not 

 logical. Exceptions occur, for instance, when low areas or 

 " storms " come into the United States from the north east of 

 the Rocky Mountains, or from the Gulf of Mexico, by way of 

 Tennessee to the lower Lakes, or skirt the Atlantic seaboard 

 without coming inland at all, having originated in the West 

 Indies. 



The influence of one of these tropical storms is revealed in 

 Series IV. The cold wave C was well defined at St. Paul and 

 St. Louis, but almost imperceptible in New York. This was 

 because its progress was obstructed and its intensity reduced 

 by the abnormal delay for five days (Aug. 21-25) of a depres- 

 sion directly ahead of it. This delay in turn seems to have 

 been due to a slight high pressure barrier along the seaboard, 

 raised, like snow in front of a plow, by the famous Martinique 

 cyclone. That storm, crossing the Windward Isles on Aug. 

 18, 1891, advanced slowly to the Bahamas, recurved there on 

 the 23d and 21th, and then crept off to the northeastward. 

 Had this interfering depression approached the Carolina coast 

 more nearly, no doubt a very different effect would have been 

 produced. The inland storm would have merged with it, escap- 

 ing quickly to the ocean ; the northerly winds in the front of 

 the anticyclone over the Mississippi Valley would have quickly 

 reached the coast, and would have been intensified. Indeed, 

 while this particular high pressure area was retarded until it 

 almost died out, the next one after it, though insignificant in 

 the west, was rendered more boisterous and chilly by the suc- 

 tion of the West India storms, which, by the 29th, was off 

 Nova Scotia. That is the day on which New York experi- 

 enced the cold wave marked C\ 



The deflection of a low area, whose center has kept north of 

 St. Paul and St. Louis, but which goes out onto the ocean south 



