536 



METEOROLOGY. 



The relations of variations of underground 

 water to precipitation and to fires caused by 

 lightning Lave been studied in Bavaria by 

 C. Lang. He finds that the height of the 

 water underground varies according to the 

 amount of precipitation. This influence is 

 somewhat obscured by the fact that the in- 

 crease corresponding to a certain increase of 

 precipitation is greater in the spring and au- 

 tumn than it is in summer. When the num- 

 ber of recorded fires caused by lightning was 

 plotted together with the record of the varia- 

 tion of underground water, the maximum of 

 one curve was found to coincide with the 

 minimum of the other. 



Mr. Blanford has found indications of a 

 periodical recurrence of droughts since 1799, 

 at intervals, in southern India, of from nine to 

 twelve years, but usually about a year before 

 the sun-spot minimum. In northern India 

 they sometimes occur in years of maximum 

 sun-spots. 



A study of the rainfall of Paris for the last 

 two hundred years has been made by M. Renon, 

 beginning with observations made by Lahine in 

 1688. At the time of Lahine there was a maxi- 

 mum in July ; now there are two less marked 

 maxima in June and September. The average 

 number of rainy days per year is 109. Snow 

 occurs very irregularly, but is never entirely 

 absent in any winter. During the period cov- 

 ered by the observations the character of the 

 situation has essentially changed ; and what 

 was a suburban tract some distance south of 

 the city is now in the midst of a dislrict sur- 

 rounded by high buildings. 



Electricity. In the observations upon the au- 

 rora borealis made by Mr. Carlheim-Gyllenski- 

 old at the Swedish station in Spitzbergen, 1882 

 -'83, the diversion of the culminating point of 

 the auroral arch from the magnetic meridian 

 was found to be 11 27' W., while the corona 

 was nearly in the magnetic zenith. The 

 breadth of the arches varies with their eleva- 

 tion above the horizon; and they consist of 

 rays running in the direction of the breadth, 

 and converging toward the magnetic zenith. 

 The greatest breadth appears to be at a height 

 of 45, while in the neighborhood of the ze- 

 nith the arches are very narrow, stretching as a 

 luminous band across the heavens. Sometimes 

 the light also formed a spherical zone parallel 

 with the earth, floating in space as a horizontal 

 rny of light. Sometimes the zone was broken, 

 with dark spots or irregular spaces. The move- 

 ments of the arches did not prove to be subject 

 to as regular laws as had been supposed: the 

 phenomena of the waves of light running along 

 the arches "the merry dancers" took place 

 nearly equally in the west to east and reverse 

 directions. The light of the aurora was yel- 

 low, monochromatic, showing in the spectrum 

 the yellow lines of Angstrom; or crimson or 

 violet, resolvable into several rays and bands. 

 No sound was ever heard from the light, or 

 " smell of sulphur" observed. The light was 



never seen to descend below the mountains or 

 the lower clouds. Measurements by parallax 

 gave average heights of from about 55 to 60 kilo- 

 metres. No annual variation in the frequency 

 of the auroras could be detected, but daily 

 ranges in frequency and form were observed. 



It was shown, by a collection of more than 

 fifty photographs of flashes, from different parts 

 of the world, at the Royal Meteorological So- 

 ciety's exhibition in March, that lightning does 

 not take the zigzag path depicted by artists, 

 but usually a sinuous and often erratic one. 

 Sometimes it had a perceptible breadth, and 

 resembled a piece of tape waved in the air. 

 One photograph illustrated a dark flash. Ac- 

 cording to the committee's report, the evidence 

 is to the effect that lightning assumes various 

 typical forms, under conditions at present un- 

 known. These forms may be classified provis- 

 ionally, as stream, sinuous, ramified, meander- 

 ing, beaded, or chapleted, and ribbon lightning. 

 Inviting photographs to be sent to the society, 

 the committee explains that the taking of them 

 does not present any peculiar difficulties. " If 

 a rapid plate, and an ordinary rapid lens with 

 full aperture, be left uncovered at night dur- 

 ing a thunder-storm, flashes of lightning will, 

 after development, be found in some cases to 

 have impressed themselves upon the plate. 

 The only difficulty is the uncertainty whether 

 any particular flash will happen to have been 

 in the field of view. A rapid single lens is 

 much more suitable than a rapid doublet ; and 

 it is believed that films on paper would effect- 

 ually prevent reflection from the back. The 

 focus should be that for a distant object, and, 

 if possible, some point of landscape should be 

 included to give the position of the horizon. 

 If the latter is impossible, then the top of the 

 picture should be distinctly marked. Any 

 additional information, as to the time, direc- 

 tion in which the camera was pointed, and the 

 state of the weather, would be very desira- 

 ble." 



A periodicity has been remarked by M. 

 Moureaux in the disturbances of magnetic 

 declination and horizontal force at Pare Saint- 

 Maur Observatory during the years from 1883 

 to 1888. The monthly values of both these 

 elements exhibit two maxima at the equinoxes, 

 and two minima at the solstices. While the 

 monthly variation of the number of disturb- 

 ances appeared to follow a general law, the 

 diurnal variation seems to be subject to com- 

 plex laws. 



In his observations on English thunder- 

 storms, which, though made in 1857 to 1859, 

 were only reported upon to the Royal Mete- 

 orological Society in 1888, Mr. G. J. Symons 

 found that in sheet-lightning the most preva- 

 lent color is white, and after it follow yellow, 

 blue, and red. In forked lightning the order 

 is nearly reversed, blue being more than twice 

 as frequent as any other color, then red, white, 

 and, most rarely, yellow. Sheet-lightning was 

 seen about twice as often as forked. 



