532 



METEOROLOGY. 



1886 March had also a minimum of 77, 

 while in January, 1885, the temperature of 

 89 was recorded. The yearly range of 

 cloud is characteristic of the climate ; in the 

 winter season the mean amounts only to about 

 three tenths in each month. 



The results of studies concerning the rela- 

 tions of pressure and temperature in high and 

 low conditions of the barometer, and at differ- 

 ent elevations, have not been harmonious. M. 

 Dechevrens concludes that, while a high tem- 

 perature accompanies a low pressure at sea- 

 level, the fluctuations are reversed at some 

 height above. Mr. H. Allen has arrived at 

 a nearly opposite result. He tries to remove 

 the disagreement by showing that the minimum 

 pressure on a mountain does not coincide with 

 the passage of a storm-center over the station, 

 but lags behind it to an extent that corresponds 

 with the height of the mountain and the sur- 

 rounding topography, and which, on the sum- 

 mit of Mount Washington, 6,279 feet, is from 

 ten to eleven hours. A like rule prevails with 

 the maximum. He also concludes that the 

 temperature change at the base precedes very 

 slightly the pressure change, but at the summit 

 the change occurs nearly twenty-four hours 

 earlier; that the temperature change appears 

 to be a very little earlier at the summit than at 

 the base, and varies much more rapidly at the 

 former ; that in a low, the difference in tem- 

 perature between base and summit is less than 

 the mean before the storm, but that it rapidly 

 increases after the center has passed. Just the 

 contrary is true in a high. 



A research by Supan on the mean duration 

 of the principal temperature periods in Europe 

 is based on observations at four hundred and 

 seventy-one stations of the length of the frost- 

 period (temperature of 0., or below), the 

 warm period (10 C. and above), and the hot 

 period (20 0. and upward), the results of 

 which are presented graphically. The lines 

 sharply mark the contrast between ocean and 

 continental climates. The lines of equal dura- 

 tion of the frost-periods, like the winter iso- 

 therms, run northward into the interior of the 

 continent in the eastern part, sometimes inclin- 

 ing to the south and southeast; those of the 

 warm periods usually keep to the parallels of 

 latitude ; while those of the hot periods run 

 decidedly to the northeast. 



Hans Fischer's charts of the equatorial limits 

 of snowfall of the northern hemisphere likewise 

 bring out the difference between land and sea 

 climates. The limit on the land runs nearly 

 along the thirtieth degree of latitude, while on 

 the sea it recedes to the thirty-fifth degree. 



The question of aperiodic variations of tem- 

 perature has been investigated by Dr. Perle- 

 witz, on the basis of observations made during 

 the forty years 18-48-1887, at Berlin, and during 

 the ninety-three years 1790-1883. at Breslau. 

 If a year is divided into halves, the first half 

 is characterized by a normal curve of rising 

 temperature, and the second half by a simi- 



larly normal curve of falling temperature. 

 Both curves, however, show negative irregu- 

 larities, the number of which may be very 

 considerable in any one month. On the whole, 

 the number of these irregularities is greater in 

 the first half of the year than in the second, 

 so that the heat of the second half is greater 

 than that of the first. 



Clouds. The British Association's Committee 

 on the Ben Nevis Observatory reported that 

 the work done there during the year had been 

 mostly directed toward obtaining a wider 

 knowledge of halos on clouds, St. Elmo's fires, 

 and other natural phenomena. St. Elmo's fire 

 was observable at definite phases of the 

 weather. The usual difference in temperature 

 between the summit and base of Ben Nevis is 

 about 16 Fahr., but in the driest season of 

 1887 it was as low as 7 Fahr. It appears that 

 when a cloud is resting upon the mountain the 

 telegraphic wire which makes communication 

 between the bae and summit has an eartli- 

 current passing through it in one direction, but 

 that after the cloud has passed over, the di- 

 rection of the earth-current changes. "Sky- 

 colored " or illuminated clouds have been 

 remarked by several observers in the northern 

 sky at night, during about six weeks near the 

 summer solstice from June 2 to July 20. 

 They are not usually colored, but shine with 

 a pearly or silvery luster. They have been 

 seen at midnight at an altitude of about 30, 

 but are more usually confined to about the 

 first 10 above the northern horizon. They 

 are supposed to be very high cirrus clouds 

 illuminated by the sun; or, by Jesse, as con- 

 sisting of small crystals, originating from the 

 condensation of gases under the low tempera- 

 ture of the upper regions of the air. 



Some light may possibly be cast upon the 

 method of formation of hail, by Mr. C. C "Wil- 

 son's observation of the drops that fell from a 

 pine-tree during a cold fog. A part of them 

 reached the ground in a liquid state, while 

 another part had been converted into pellets 

 of ice. The author believes that the ice-drops 

 came from the upper part of the tree, having 

 been frozen during their traverse of the greater 

 distance by the greater loss of heat which they 

 suffered from the more rapid and longer-con- 

 tinued evaporation. An instance is mentioned 

 in which a railway-train became coated with 

 ice, in traveling through an atmosphere above 

 the freezing-point, and laden with mist. 



After continued studies of the " red sunsets " 

 which were prominent features of the skies from 

 the end of August, 1883, to June, 1886, Kiess- 

 ling has concluded that they were due to no 

 other cause than the vapors mingled with 

 combustion-products which were thrown up 

 into the atmosphere by the volcanic explosion 

 of Krakatoa on the 27th of August of the for- 

 mer year. He is convinced, from experiments 

 with mechanically produced dust, that the solid 

 ejecta the finely powdered pumice-stone, con- 

 stituting a large part of the volcanic ash had 



