METEOROLOGY. (TEMPERATURE.) 



533 



next morning, are more or less completely lost 

 sight of as the cyclones grow in strength and in 

 rapidity of movement. The obliteration consists 

 in the continuous rise of temperature from one 

 day to the next through the night, or, converse- 

 ly, the continuous fall of temperature from one 

 night to the next through the intervening day. 

 The lowest, temperatures are recorded during the 

 winter anticyclones ; and the records of adjacent 

 hill and valley stations vary greatly, the lowest 

 of nocturnal minima being always in the valleys, 

 while the hills have less extreme cold ; and on a 

 commanding summit, like that of Mount Wash- 

 ington, the temperature is distinctly moderate. 

 The ariticyclonic days are the finest of the season, 

 with an air dry and inspiriting and a bearable 

 cold, quite unlike the penetrating blast of the 

 cold wave or the searching chill of the winter 

 northeaster. These spells are brief. The ap- 

 proach of the cyclone is marked by a damp, sul- 

 try wind, under which the temperature gradu- 

 ally rises, particularly in the higher layers of the 

 atmosphere. The winter snow and rain come 

 chiefly from these winds in front of cyclones. 

 The exact character of the weather is modified 

 by the position of the track of the cyclone with 

 reference to New England. If the track lies to 

 the north, the precipitation is likely to be rain. 

 When the center traverses New England, snow 

 generally falls. An exceptional occurrence asso- 

 ciated with the blowing of the warm wind before 

 the cyclone is the occasional production of iso- 

 lated high temperatures in the northern valleys 

 of the White Mountains. The " ice storm " which 

 sometimes attends the approach of a cyclonic 

 rain after an anticyclonic cold spell is supposed 

 to result from the rain formed in a warm upper 

 stratum of air passing through a cold lower stra- 

 tum, where it is cooled close to the freezing point. 

 The rise in temperature preceding the cyclone is 

 reversed to a rapid and steady decrease as the 

 storm passes and brings up the westerly and 

 northerly winds of its rear, and the cold wave is 

 introduced. This being an active wind, its low 

 temperatures are pretty uniformly felt on hills 

 and in valleys. If there is any difference the hills 

 are the colder. The change is sometimes accom- 

 panied by thunder storms. The quality of the 

 change depends on a variety of conditions, which 

 are summarized in the paper. It is at the periods 

 of cold northwesterly winds on the lowlands that 

 the upper wind is strongest and its cold most in- 

 tense. With the coming of April and the gen- 

 eral disappearance of snow in the interior and 

 the warming of the ground under sunshine of 

 increasing strength and length, the cold waves 

 are warmed before reaching New England. A 

 new feature characteristic of this change of sea- 

 son is the warm and often dry southwest wind ; 

 another highly characteristic feature is the in- 

 creasing importance of the true diurnal range in 

 clear weather, especially under anticyclones, and 

 the high temperatures reached by the maxima 

 at such times. The sea breeze is now first felt 

 on the coast, and exerts a decided influence in 

 lowering the diurnal temperature maximum ; 

 but it penetrates only a few miles inland. The 

 spells of southerly winds become in midsummer 

 the occasions of highest temperature. The cu- 

 mulus clouds attain a greatly increased volume 

 and height. Later in the warm season, fair 



weather, with mountainous clouds floating in 

 light winds and dissolving at night, may char- 

 acterize a number of days in succession, imitat- 

 ing the orderly succession of events that prevails 

 throughout the year in the torrid zone, where 

 diurnal changes are the rule and cyclonic changes 

 are the exception. Thunder-storms are com- 

 monly formed at such times as this. 



A paper, by Dr R. J. Suring, on the " Vertical 

 Decrease of Temperature with Height in Mount- 

 ainous Districts, and its Dependence upon the 

 Amount of Cloud," embodies the results of ob- 

 servations at mountain stations up to the height 

 of about 4,100 feet. The author finds that in 

 the morning, when the weather is clear, there is 

 a constant tendency to an inversion of tempera- 

 ture. In summer this tendency extends to some 

 1,650 feet, and in winter considerably higher. 

 The same condition recurs in the evening on a 

 smaller scale. A departure from the law of 

 "direct proportional decrease of temperature with 

 height occurs chiefly during the morning hours 

 of clear days, the change of temperature then 

 taking place more slowly in the lower strata of 

 air than in the upper ; and on cloudy days dur- 

 ing the warm season, when in the lower strata 

 the vertical decrease is accelerated. 



Hourly observations on the nocturnal tempera- 

 ture of the air at different heights up to 24 feet, 

 made by M. J. Juhlin, at Upsala, during the win- 

 ters of 1887 and 1888, showed that the decrease 

 of temperature by radiation from unprotected 

 thermometers over snow remained almost con- 

 stant at heights above half a metre. During clear 

 nights the temperature increased with the height 

 from two to three hours before sunset until two 

 hours after sunrise, and the lower the tempera- 

 ture the greater was the increase. During 

 cloudy or foggy nights the temperatures at dif- 

 ferent heights were nearly equal. The surface 

 of the snow was colder than the surrounding air. 



Observations on the summit of Pike's Peak, 

 14,134 feet above the sea the highest meteoro- 

 logical station in the world between January, 

 1874, and June, 1888, show that- the maxima of 

 both pressure and temperature occur in July, and 

 the minima in January. The annual march of 

 both elements is the same, and the two curves 

 are almost coincident. The mean temperature 

 for the whole period of the observations was 

 19-3 F. ; the maximum observed was 64, and 

 the minimum 39. The maximum daily range 

 occurs in September (about 14'3), and the mini- 

 mum in December (11'6, or only half of the 

 range on the low plateau country to the east- 

 ward). Of the precipitation, 35 per cent, falls in 

 the summer, and 33 per cent, in the spring, the 

 maximum occurring in July and the minimum 

 in February. The mean wind velocity decreases 

 gradually from 26'6 miles per hour in January to 

 12-5 miles in July, and 12-3 in August, and it 

 decreases from between two and four o'clock in 

 the morning till between eleven o'clock and noon. 

 The mean hourly velocity during any day rarely 

 exceeds 50 miles. The prevalent direction of 

 winds is from southwest to northwest. Electri- 

 cal storms, though frequent, occur only when 

 the air is moist. 



It is calculated by M. Forel that the amount 

 of heat accumulated in Lake Leman during the 

 summer of 1889 was equal to that which would 



