July 9, 1891] 



NATURE 



229 



degree distinct and forcible, not merely of the objects 

 themselves, but even of the greatly altered intensities of 

 light under which we view them. . . . Thus the imitation 

 of Nature in the picture is at the same time an ennobling 

 of the impression on the senses.'' 



Let me congratulate you on the fact that here, at all 

 events, the importance of physical science in its relation 

 to art is not forgotten. J. Norman Lockykr. 



LUMINOUS CLOUDS. 



T N an article contributed to Nature on November 20, 

 -*■ 1890 (vol. xliii. p. 59), Herr O. Je-se (of the Royal 

 Observatory of Berlin) gave an account of his observations 

 of luminous clouds. He has recently submitted to the 

 Prussian Royal Academy of Sciences a record of later 

 work ; and, as the subject is one of considerable interest, 

 it may be worth while to translate his paper.^ 



With regard to the results, already briefly noted, obtained 

 in the summer of 1890, I have now to report more pre- 

 cisely, that with the help of the grant made by the 

 Academy of Sciences we were able, during the period 

 when the phenomenon appeared, to secure a collection of 

 photographs which afford rich material for study. 



On this as on previous occasions the clouds were visible 

 only between the end of May and the beginning of August. 

 They appeared for the first time, in 1890, on May 26 ; for 

 the last time—and then there was only a feeble trace of 

 them — at the beginning of August. The phenomenon, 

 therefore, was seen within nearly four weeks of the sum- 

 mer solstice— before and after it— but chiefly after it. 



Since my last report, I have received confirnntion 

 of the statement that the time when the phenomenon 

 appears in the southern hemisphere has a corresponding 

 relation to the summer solstice there. Unfortunately, 

 however, more precise facts with regard to place, &c., in 

 the southern hemisphere, are still lacking. 



During the period between May 26 and July 24, 1890, 

 we obtained altogether 180 photographs of luminous 

 clouds at Steglitz, Rathenow, and Nauen, and at the 

 Observatory of Urania, Berlin. Of these photographs, 75 

 are suitable for the determination of height, inasmuch 

 as they were secured at the same time in at least two 

 different places. Thirty of the photographs may be used 

 for the determination of the speed and direction of the 

 movements of the clouds, because their representations 

 of the clouds were taken at proper intervals at one and 

 the same place. The remaining photographs are adapted 

 for investigations relating to the dimensions of the clouds 

 and their structure. 



The phenomenon was again less bright than it had 

 been in the preceding year. Only when the atmosphere 

 was exceptionally transparent was there an approach to 

 the former brilliancy. The aggregations of these masses 

 of particles are obviously becoming thinner, as may 

 also be perceived from the more distinct appearance of 

 certain relations of structure, like the ridge and rib 

 formations (wave formations) mentioned m my last 

 report Formerly these were concealed by superposition 

 and apparent interference of a greater richness of analo- 

 gous strata ; now the characteristic lines of the configura- 

 tions consisting of these ridge and rib formations present 

 themselves more simply and in greater isolation. 



It has now been proved inore successfully than before 

 that the ridges or longitudinal strips lie parallel to, while 

 the ribs or cross strips are almost at righc angles to, the 

 direction of the movement of the entire cloud. Further, 

 we made on different days several series of measurements 



' "Sitzungsberichte der Konig'ich Preussischen Akademie der Wis>en- 

 schaften zu Berlin," 1891, xxvi. Si iiing der physikalisch-m.nthematlschen 

 da^se, vom 28 Mai. •' Untrrsuchungen (iber die sogenannten leuch enden 

 Wolken," von O. Jesse, Steglitz. 



NO. I 132, VOL. 44] 



of the distances of the ribs (wave-crests) from one another 

 with the following groups of results : — 



-, 1 r 1 ■!• .- Kilom. 



Mean value of the distances of 9 wave-crests ... 83 



10 „ ... 99 



Average 



8-9 



Especially striking, last summer, was the difterence 

 between the clearness with which the clouds appeared in 

 the morning hours, and that with which they appeared at 

 the corresponding times before midnight. 



With regard to the height of the luminous clouds in 

 the summer of 1890 the measurements, so far as they 

 were definitely calculated, gave the mean value of 82 

 kilom., agreeing almost exactly with the value of nearly 

 83 kilom., deduced from my photographs of 1889. 



The persistence from year to year —now for the first 

 time shown with sufficient accuracy — of the distance, 

 and therefore of the position of the level surface of the 

 phenomenon, would alone deserve to be recorded as a 

 scientific fact of .^reat importance. 



As for the speed and directions of the movements, 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 metre-i in the second 

 from west to east. 



The e was also a smaller and variable component in 

 the direction of the meridian. This was directed from 

 north to south at the times at which we hive hitherto 

 obtained tolerably secure determinations of movement. 



The points of view from which the phenomenon of 

 luminous clouds, on the ground of the observations 

 hitherto made, is to be regarded, are already numerous. 

 There is still, however, a wide field for research in con- 

 nection with the questions. What are the forces which 

 make the phenomenon appear chiefly in the morning 

 hours? and. What is the nature of those forces which 

 cause the movement of the clouds to be mainly from the 

 north-east, and drive them from the northern to the 

 southern hemisphere and back again ? Then the question 

 as to the height of the phenomenon in different latitudes 

 is probably of greit importance for the constitution of our 

 atmosphere ; and not less interesting is the question 

 relating to the material of which the luminous clouds are 

 composed. Unfortunately the interest taken by the 

 scientific world in this remarkable phenomenon is in 

 general so small that during the short time the phe- 

 nomenon will probably present itself we can scarcely 

 expect to obtain for these questions answers that shall be 

 to any considerable extent satisfactory. 



WILHELM EDUARD WEBER. 



T^HE venerable physicist, Wilhelm Eduard Weber, 

 ■*■ whose death on June 23 we shortly announced 

 last week, was born at Wittenberg on October 24, 

 1804, the second of three sons of Michael Weber, Pro- 

 fessor of Positive Divinity at Wittenberg. He studied at 

 the University of Halle, where Schweigger was then 

 Professor of Physics ; he took his Doctor's degree in 1826, 

 became Privatdocent in the following year, and Professor- 

 Extraordinary of Physics in 1828. In 1831 he was called 

 to Gottingen to succeed Jo'iarn Tobias Mayer in the 

 Chair of Physics, and remained there till 1837. Among 

 other results of the death in this year of King William 

 IV., there came about serious changes in the University 

 of Gottingen. Queen Victoria being excluded fro n the 

 throne of Hanover, by the operation of the Salic law, her 

 uncle, Ernest Augustus, Duke of Cumberland, became 

 King of Hanover. This prince held high views as to the 



