44 



SCIENCE. 



[N. S. Vol. II. No. 28. 



logical conditioBs of Spitzbei'gen are veiy fa- 

 vorable for a loag feronaiitical voj^age. The 

 sun in July never sinks below the horizon, 

 and the variations of temperature are con- 

 sequently very slight. The lowest temper- 

 ature observed in July, 1883, at Cape Thord- 

 sen, was -(-0°.8 and the highest, +11°. 6. 

 At Spitzbergen, during the first fortnight 

 in August, 1892, the largest daily variation 

 observed was 3°, and as a rule it was not 

 greater than 1°.5. The movements of the 

 baloon would therefore be very regvilar. 

 There is no storm to be feared in the polar 

 regions. The rainfall is small, and a fall of 

 snow at this time of the year would be no 

 obstacle to the baloon. 



THE UPPER REGION OF THE ATMOSPHERE. 



According to the London Times, at the last 

 meeting of the Eoyal Institution for the 

 present season Professor Alfred Cornu, F. 

 E. S., of the Paris Academy of Sciences, de- 

 livered an address in French on the ' Les 

 Phenomenes Physiques des Hautes Regions 

 de I'Atmosphere.' 



M. Cornu began by comparing the atmos- 

 phere to an immense thermo-dynamic en- 

 gine, the sun being the source of heat and 

 the interplanetary space the condenser. 

 The most interesting phenomena took place 

 in the almost inaccessible parts of the at- 

 mosphere, and though the difBculties of 

 getting information about those elevated 

 regions were great, yet he hoped to show 

 that the physicist was beginning to know 

 much of the real explanation of natural 

 phenomena and was even able to reproduce 

 them in his laboratory. Among the unex- 

 pected static phenomena discovered by bal- 

 looning and in mountain observatories M. 

 Cornu instanced three — namely, the facts 

 that many clouds which had generally been 

 regarded as consisting of vapour were com- 

 posed of minute ciystals of ice ; that at 

 different heights the direction of the wind 

 was different ; and that the temperature 



did not get steadily lower as the earth be- 

 came more distant, but that alternate lay- 

 ers of hot and cold air were encountered. 

 The first and last of these facts might have 

 been ascertained by indirect means from 

 consideration of certain optical j)heuomena. 

 From the solar halo might be inferred the 

 presence of ice crystals in cirrus cloud; 

 they had the power of refracting light, and 

 refraction of the sun's light by passing 

 through cloud would fully explain the halo. 

 It could be reproduced artificiallj^ by pass- 

 ing a beam of light through a strong solu- 

 tion of alum, with a little alcohol added. 

 The alternations of heat and cold in the 

 atmosphere were deducible from the various 

 forms of mirage, which depended on the 

 reflection of light from the surface of the 

 different laj'ers. M. Cornu. gave an inge- 

 nious reproduction of the 'Alpine glow,' 

 sometimes seen in the Bernese Oberland, 

 for an example. A valley between two 

 peaks would become filled with hot air un- 

 der the influence of the sun, and the path 

 of the rays of light reflected from the sur- 

 face of the hot layer would be convex as 

 regarded from the earth. After sunset the 

 hot air would rise and the cool take its 

 place, thus producing a hot laj^er of air 

 above of a cooler one. The light from the 

 sun would now be reflected into a concave 

 ray, which would bend down and illumi- 

 nate the mountain, though the sun was in 

 fact below the horizon. M. Cornu then 

 proceeded to speak of the djTiamic phe- 

 nomena of the air. He said that the solar 

 energy was of three kinds — mechanical 

 energy (appearing as winds, cj'clones, etc.), 

 calorific energj^ (shown bj^ the change of 

 the state of matter, as of water into vapour), 

 and electrical. He oulj' proposed to deal 

 with the first of these. The wind was the 

 most simple mechanical manifestation and 

 had its origin in the difference of atmos- 

 pheric pressure in two distant places. It 

 never blew in the direction of the line join- 



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