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METEOROLOGY. 



now been proved more successfully than before 

 that the ridges or longitudinal strips lie parallel 

 to the directiou of movement of the entire cloud, 

 while the ridges or cross strips are almost at 

 right angles to it. The measurements of heights, 

 so far as they were definitely calculated, gave a 

 mean value of 82 kilometres, which agrees closely 

 with the value of nearly 83 kilometres deduced 

 from the photographs of 1889. It was again 

 found that the chief component of the move- 

 ment was directed from east to west, and 

 amounted to nearly 100 metres in the second, 

 while the speed of the revolution of the zone of 

 the earth above which the clouds were placed is 

 about 240 metres in the second from west to 

 east. There was also a smaller and variable 

 component in the direction of the meridian, or 

 from north to south. While the points of view 

 from which the phenomena may be regarded on 

 the ground of the observations already made are 

 numerous, there is still a wide field for research 

 in connection with the questions : What are the 

 forces that make the phenomenon appear chiefly 

 in the morning hours! What is the nature of 

 those forces that cause the movement of the 

 clouds to be mainly from the northeast, and 

 drive them from the northern to the southern 

 hemisphere and back again? The luminous 

 clouds were again visible in 1891 on June 25-26 

 at Steglitz and Nauen, and were photographed 8 

 times simultaneously at those two places. They 

 were also seen by Mr. T. W. Backhouse at Sun- 

 derland, England, and Mr. D. J. Rowan at Kings- 

 town, Ireland, on the night of June 30. At Sun- 

 derland their motion was, " as usual, from a 

 northeasterly direction," and at Kingstown they 

 " appeared well-developed on a polar arc of 30 

 and at a mean altitude of 5." They had been 

 faintly visible at Kingstown early in June. Ob- 

 servations of them for 1892 are mentioned by 

 W. Clement Ley, at Lutterworth, England, on 

 the night of June 24 ; and they were seen from 

 the summit of Ben Nevis all through the night 

 of June 24-25. A special appeal is made by W. 

 Foerster and 0. Jesse to astronomers and geo- 

 physicists in different countries to make observa- 

 tions of these phenomena. The clouds have been 

 more rarely seen in recent years than in the 

 earlier years of observation, beginning with 1885. 

 Their appearance is subject to great changes. 

 While they frequently exist only in a few little 

 luminous stripes or patches, they appear at times 

 in greater accumulations and with a more intense 

 light. Frequent observations of the movements 

 of the clouds render it probable that they are 

 caused principally by the resisting medium of 

 the mundane space. In accordance with this is 

 the fact that in the half year after its appear- 

 ance in Berlin the phenomenon has been observed 

 repeatedly in the southern latitude of 53 by 

 the meteorological observer, Mr. Stubenrauch, in 

 Punta Arenas, as well as several times by ship 

 captains ; and other observations are cited in 

 confirmation of an annual wandering of this 

 kind. Persons interested in furthering the so- 

 lution of the questions suggested in these phe- 

 nomena are therefore invited to co-operate in 

 the study of them. 



An envelope of vapor is supposed by Herr von 

 Frank, of Gratz, to explain the floating of 

 particles of cloud or fog. The lengthening of 



shadows when clouds pass over the sun is at- 

 tributed to refraction by the vapor envelopes. 

 It is difficult to see how water droplets in the 

 form of cloud or fog could exist at such vari- 

 ous temperatures did not the vapor envelopes, 

 as bad conductors of heat, guard them to some 

 extent from evaporating and freezing. The 

 minute particles must soon be dissipated by 

 the sun's rays if they were not in a kind of 

 spheroidal state. This heating expands the en- 

 velopes, so that the cloud tends to rise, and 

 various phenomena in nature may be thus ex- 

 plained, such, for instance, as the rise of mist in 

 Alpine valleys. Liquid droplets have been ob- 

 served by Arsmann floating in an air of -10 0. 

 On meeting a solid body, these froze to ice 

 lumps without crystalline structure. Here, ac- 

 cording to Herr von Frank, the vapor envelopes 

 prevent freezing, till they are ruptured by the 

 solid ; the droplet thus loses the bad conductor 

 of heat that protected it, and solidifies so quickly 

 that no crystals can form. The author supposes 

 that with much aqueous vapor in the air larger 

 drops form, the clouds floating lower ; with less 

 aqueous vapor, the drops are smaller and the 

 clouds higher; the thickness of the envelope, 

 however, being the samefor large and small drops 

 under like conditions of the temperature and 

 pressure. 



One of the most notable facts brought out by 

 A. L. Rotch's measurements of cloud heights 

 and velocities at the Blue Hill Observatory, 

 is the difference in height between the same 

 clouds in summer and winter ; the clouds, with 

 few exceptions, being lowest in winter. The 

 bases of the cumulo-nimbus clouds, however, 

 are generally lower in summer, while their tops 

 are higher than in winter. The heights of 

 the different clouds were found to maintain an 

 almost constant ratio to each other. The mean 

 velocities recorded showed that the entire atmos- 

 phere moves twice as fast in winter as in summer. 

 The mean velocity of the highest clouds in 

 winter was about 100 miles an hour ; the ex- 

 treme velocity amounted to 230 miles an hour, 

 from which it appears that the upper currents 

 are much more rapid over America than over 

 Europe ; and this possibly explains the greater 

 velocity of the storms in America. The tables 

 show, as to the directions of cloud movement, 

 that from the highest clouds to the earth's sur- 

 face the prevailing wind is west ; above 4,000 

 metres, more than 90 per cent, of the observa- 

 tions show the clouds moving from some point 

 between south and west and northwest inclusive. 

 In the cirrus and the cumulus regions, and near 

 the earth's surface, the prevailing direction is 

 from a little north of west, but in the intermediate 

 levels from a little south of west, the excess of 

 the southerly component in those regions being 

 possibly due to the influence of cyclones. 



Pressure. In a report of researches into the 

 daily oscillations of the barometer, Dr. J. Hann, 

 of Vienna, deals with a thorough analysis of the 

 barometric oscillations on mountain summits 

 and in valleys, for different seasons, for which 

 he has calculated the daily harmonic con- 

 stituents, and has given a full description of the 

 phenomenon, showing how the amplitude of the 

 single daily oscillation first decreases with in- 

 creasing altitude, and then increases again to a 



