70 



SCIEXCE. 



[Vol. VII., No. 155 



60 ft.; lat., 20° 21' S.; long., 175° 28' W. position 

 of Sandfly Island, for we saw it rise. Got back 

 again just too late to enter the reefs to Tonga. 

 Anchored at Nukualofa at ten a.m. on the 15th. 

 We had lovely weather all the time, a nice S. E. 

 wind, and every one seemed highly gratified with 

 what he had seen.' " 



THE RECENT COLD WAVE. 



The accompanying minute maps are reduced 

 from daily weather-charts published by the signal 

 service, and represent certain features of the 

 weather during the passage of the recent severe 

 cold wave. The series of six maps (figs. 1 and 2). 

 designed to show the changes of temperature from 

 Jan. 7 to Jan. 12, are crossed by a heavy line that 

 marks the altitude of 0° F. as determined by the 

 observations at 7 a.m. on successive mornings. 



the same time an area of high pressure, with very 

 low temperatures, stood in the far north-west. 

 As is stated by Lieutenant Woodruff in his recent 

 note on cold-waves, areas of high pressure extend 

 to the south and east with their low temperatures, 

 while the antecedent storm-centres move off to the 

 north-east. The wave here considered belongs to 

 the third of Woodruff's classes, inasmuch as it first 

 spread south ward to Texas, and then east and north- 

 eastward to the Atlantic coast. On Jan. 8, when 

 the storm-centre was near Mobile, a fine ' norther,' 

 such as would have delighted Redfield, swept down 

 the plains to the Gulf, and Galveston was only 

 about ten degrees warmer than Duluth. The zero 

 isotherm stood just west of the Mississippi, run- 

 ning nearly north and south for about seven hun- 

 dred miles. During the next three days, while 

 the storm moved off over Labrador, the cold wave 

 crept up the Ohio valley, where the temperature 



Fig. 1. 





35? 



' !: >^l^^.-^3'' Jan/2 





' 7' • 



Fig. 2. 



To the north of it, the dotted area extends to th e 

 isotherm of 80° below zero ; the space shaded with 

 lines, farther north, being colder still. The un- 

 shaded part of the maps contains the tempera- 

 tures between 0° and 30° above ; the next belt 

 covers temperatures from 30° to 50°; and in a few 

 of tin- maps, temperatures .above 50° appear in the 

 extreme south. 



On the morning of Jan. 7, a storm-centre of 

 moderate intensity lay in southern Texas, having 

 eome across northern Mexico from the Pacilic ; at 



then stood distinctly lower than in Michigan, two 

 hundred miles farther north. At last, on Jan. 11 

 and 12, the zero isotherm turned well north over 

 the plains as more moderate temperatures re- 

 turned. 



The most interesting phase of this spell of 

 weather was doubtless that presented on the 

 morning of Jan. 9, when the storm had developed 

 into a true cyclone, with nearly circular isobars, 

 and remarkably low pressure at its centre in 

 southern New Jersey. At this time the barometer 



