41 



NATURE 



{Feb. 28, iii84 



clouds (25,000 feet) ; </, the plane of the August meteors — 

 beginning and ending (155 and 9S km.) ; f, the point of 

 appearance and disappearance of the large meteor which 

 was seen on March 4, 1S63, in England, Holland, Belgium, 

 and Germany (134 and 26 km.) ; and finally ,(,■', the hypo- 

 thetical height of the atmosphere (10 geographical miles 

 = 74 km.). 



With regard to the results of the measurements of the 

 aurora which I effected during last winter at Kautokeino, 

 in conjunction with the stations at Bossckop and Sodan- 

 kylii, I may be brief, from the circumstance that the 

 observations made at the latter station are not to hand, 

 while the material at my disposal requires a more careful 

 analysis than I have as yet been able to bestow upon it. 



I must, however, state that a preliminary examination 

 of the observations made in the plane Kautokeino- 

 Bossekop has led to the important discovery that the 

 aurora borcalis, at all events in this locality, lies in a 

 plane at least 100 km. above the earth. I have examined 

 all the observations made simultaneously at the two 

 stations, and have not found the slightest indication of 

 the aurora descending to a level in which it would only 

 be visible at one of them, while there seems to be no 

 reason for assuming that the types observed were not 

 identical, when due regard is paid to the difference in the 

 height above the horizon of the two stations." The dis- 

 tance between Kautokeino and Bossekop is about 107 km. 



I have, on the principle indicated in Fig. i, made a 

 series of preliminary measurements of the lower edge of 

 aurora observed at both stations, having selected only 

 those where there cannot be the least doubt as to identity, 

 from which I have obtained the following values in kilo- 

 metres : — 760, 799, S4-6, 93-6, 977, 98-2, 99'o, 1000, 

 ioo'6, io7'o, ii6'6, i24'i, I24'9, I3r9, I4r6, i44'9, 1490, 

 163-6. 



If the average of these eighteen measurements is taken, 

 the average height of the lower edge will be 113 km., i.e. 

 a result which is in perfect harmony with the later obser- 

 vations referred to above. 



To give any definite results of the studies of the thick- 

 ness of the arcs, the length of the streamers, &c., is, of 

 course, impossible, until the material has been carefully 

 sifted. I may here in passing observe that we must in all 

 estimates of the height of the aurora borealis be content 

 with approximate figures ; this lies in the nature of the 

 case, apart from inaccuracies in the measurements which 

 it is impossible to avoid. The aurora borealis has, in 

 common with clouds, no absolutely defined and fixed line 

 of extension, either downwards nor upwards. We must 

 therefore rest content with ascertaining only approxi- 

 mately the height of the plane in which the aurora borealis 

 appears. 



That the aurora generally appears at a height of 100 km. 

 or more above the earth's surface does certainly not pre- 

 clude the possibility of its appearance on some occasions 

 much nearer the earth. In fact there are a considerable 

 number of reports in our hands which imply that this is 

 really the case. Thus observ'ers aver that they have seen 

 aurora? below the clouds, in front of mountains and ice- 

 bergs and coasts, and even on the very ground. These 

 assertions have been greatly doubted as being the result 

 of the imagination, or optical illusions, but with what 

 justice I will not venture to say. For my own part I can 

 only say thit during my long stay at Kautokeino I had 

 unfortunately often enough occasion to observe aurorse 

 and clouds simultaneously, but although always paying 

 the closest attention to this particular point I have never 

 seen even a fragment of an aurora in front of or below 

 the clouds. Even the most intense development of light, 

 colour, and motion occurred always above what seemed 

 to be the very highest-lying clouds. 



' The experiences of Prof. LemstrUm at Sodankyhi (Mature, \A. xxvii. 

 P- 389), which seem to piint in a different direction, I intend to discuss on 



When the entire material relating to the study of the 

 aurora borealis has been collected from the various inter- 

 national circumpolar stations, sifted and carefully analysed, 

 the question of the height of the aurora borealis will not, 

 I believe, long remain one of the unsolved problems of 

 nature. Until then the reader must remain content with 

 the discoveries I have indicated in this paper. 



SOPHUS Tromholt 



COUNT DU MONCEL 



/""OUNT THEODORE DU MONCEL, whose death 

 ^^ we briefly announced last week, was born at Paris 

 on March 6, 1821. His father had been a General of 

 Engineers under Louis Philippe, and the son was at one 

 time destined also for the army. When but eighteen 

 years of age he showed a predilection for scientific 

 pursuits, and published two treatises on perspective, 

 treated mathematically and artistically. He was also at 

 this time an enthusiastic archa:ologist and traveller. In 

 1847 he published a volume entitled: " De Venise <i 

 Constantinople a travers la Grece," illustrated with 

 lithographic plates drawn by himself. His family ob- 

 jected to his democratic pursuits, and became estranged 

 from him. In consequence he determined to adopt 

 science as a profession. But not having studied at the 

 Ecole Polytechnique, nor at the Ecole Centrale, he lacked 

 those scholastic recommendations without which, in 

 France, promotion is so difficult. A professorship being 

 absolutely closed to him, he became a scientific writer, 

 and devoted his attention chiefly to electricity. In the 

 years which followed he zealously sought to acquaint 

 himself with every new discovery and invention whi:h 

 was made ; and his industry in collecting and dissemi- 

 nating information on electric science was immense. 

 During the years 1854- 1878 he published at intervals in 

 five volumes, his well-known "Exposd des Applications de 

 I'Electricite," a work which, though it relates chiefly to 

 inventions and instruments now superseded by newer 

 forms so abundantly poured forth during the past few 

 years, nevertheless maintains its place as a standard 

 work of reference in electric technology. Since 187S 

 Count du Moncel published several volumes containing 

 popular expositions of various branches of the science. 

 His work on the Telephone and Microphone has been 

 translated into English ; so also has his work on Electric 

 Lighting, and that on Electricity as a Motive Power. 

 Thoroughly in his element as a writer for the scientific 

 press, and more of a journalist than a man of science. 

 Count du Moncel nevertheless distinguished himself by 

 a series of valuable contributions to science, chiefly in 

 the form of papers read before the Acad^mie des Sciences. 

 His researches on the properties of electromagnets and 

 on the conductivity of badly-conducting bodies are worthy 

 of mention. To du Moncel we owe the observation that 

 the variation produced by pressure in resistance offered 

 at the point of contact between two conducting bodies — 

 a phenomenon well known before his time — is more 

 marked in certain bodies than in others, w-ood-charcoal 

 being one. In this observation he laid the foundation for 

 thesubsequentapplications of this principlemadeby Cldrac 

 and by Edison. Du Moncel was also an inventor, and ob- 

 tained a gold medal at the Exposition of 1855 for the collec- 

 tion of instruments exhibited by him, including an electric 

 water-indicator, an electric anemograph, an electric 

 recorder of improvised music, a recording galvanometer, 

 and sundry telegraphic instruments. From i860 to 1873 

 du Moncel was occupied as electrician to the administra- 

 tion of telegraphs ; but he quitted the post somewhat 

 abruptly in 1873 in consequence of disputes in the ad- 

 ministration. In 1874 he was elected a member of the 

 Academic des Sciences, in which body he was very active 

 in bringing forward accounts of all discoveries in his 

 favourite science. It was he who thus sviccessivelv intro- 



