492 



ELECTRICITY. 



The preceding phenomena admit of a ready explana- 

 tion, u|X)ii the simplest principles of electricity. As 

 snow is a conductor next in order to water, and \ cry 

 little inferior to it in its power of transmitting electri- 

 city, it is quite obvious that the bodies of the travellers 

 were not overcharged with the electric fluid in conse- 

 quence of any difficulty which it experienced in pac- 

 ing into the earth. Tlieir fingers therefore acted like 

 Mount Mi- to many points in drawing electricity from an atmo- 

 ** sphere highly charged, just in the same manner as when 



the hand or the head is presented to an electrified prime 

 conductor. The variety in the character, as well as 

 in the intensity, of the sounds which were produced at 

 the points of their fingers, arose from the different ve- 

 locities of their fingers, and may be readily imitated by 

 any other specie* of sound. The buzzing noise which 

 M. Jalabert heard round his head had a different origin, 

 having been produced by the discharge of the electric 

 matter which had lieen accumulated in the gold band, 

 nnd which found a readier escape into the atmosphere 

 by the numerous points of gold thread, than by the im- 

 {>erfect conducting power of the hat which it encircled. 



For farther information on the subject of this Section, 

 aee Nollet Lemons de Physique, torn. iv. p. 34 ; Paccard 

 in Saussure's Voyages dans les Alpes, torn. iii. p. 79. 

 Note ; Franklin's Letters, p. 44 ; Romas, Memoires des 

 Savons Etrongrr.t, torn. ii. p. 393, torn. iv. p. 514; Bec- 

 caria Letlere Sell Elettricismo ; Cassini, Hist. Acad. Par. 

 \15'2, p. 10; Canton, Phil. Trans. 47 ; Bevis, Id. ; La 

 Gardi, Journal des Scavans, 1753, Oct p. 222 ; Verrat, 

 Comment. liononienses, torn. iii. p. 200 ; Muschenbroek, 

 torn. i. p. 397 ; Lamanon, Phil. Trans, vol. xlvii. p. 

 272; Gallitzin, Observations sur f E/ectricile Nalurelle 

 par le moyen d'un ccrf-folant ; Bertholon, De I' Elec- 

 tririte dei Meleoret, torn. i. p. 66. 



The following references are to works containing facts 

 respecting ascending lightning : Maffei DcHaformazione 

 rl<-l fulmiiii ; Ceneda Journal tic I'enise, torn, xxxii. 8 ; 

 TormeyElogesdeAcailemicirn.^tom. ii. p. 97; Mem. Acad. 

 Par. 1755, ~p- 28 ' > Chappe, Mem. Acad. Par. 17<)7, p. 

 314; Chappe Voyage en Calif ornie, j>. 34 ; La Lnnde 

 Journal des Sava'ns, Nov. 1775, p. 766; Cotte Journal 

 des Savant, Jan. 1777, p. 34 ; Journal Encyclopedique, 

 llth May, 1778, p. 105; Ferris in Rozier's Observa- 

 tions, ffc. 1783, p. 178 ; Le Gentil Voyage dr.ns les mers 

 de F Inde, torn. ii. p. 659 ; BinVart in Rozier's Obser- 

 vations, %c. 1789, torn. ii. p. 279 ; Lamanon in Rozier's 

 Observation!:, 1784, p. 13 ; Lorgna in Rozier's Oberva- 

 lions, ffc. Nov. 1 782 ; Gallitzin Lettre stir (juclqiiex <>!>- 

 'jels D' Etectricite, Hayel778; and particularly Ber- 

 tholon, De I' Electricite des Mttcores, torn. i. p. 132. 

 chap. iv. See Part II. for an account of the construc- 

 tion and use of conductors and thunder rods. 



8. On the Electricity exhibited in the production of lumi- 

 nous Meteors. 



ttn the dec- The Aurora borealis is undoubtedly the most magnifi- 

 uidty of lu- cent O f all the luminous meteors, which appear to be pro- 

 duced by the agency of electricity. In our article on 

 that subject, (see AURORA BOHF.ALIS,) we have already 



given an account of the various theories which have Daorijt; 

 been brought forward to explain this remarkable ap- 

 pearance, and have {minted out it- connection with the S ^"Y""* > 

 phenomena of electricity. Almost every philosopher, Aurora bo. 

 indeed, has adopted this opinion, and all the theories realu - 

 of the aurora borealis, with the exception ot' that of 

 Monge, have called in the :ti<! of electricity, either as a 

 primary or a secondary agent. In the theory of M. 

 Libes, for example, he supposes that a mixtin 

 and hydrogen is inflamed by the action of the I (.-trie- 

 spark ; and M. Dalton, who considers the aurora I 

 as a magnetic phenomenon, still supixjses that th li^ht 

 is produced by the transmission of the electric ft 



Monge has ascrilied the aurora boreal H to t'ie 11- ht of IlcfutaUon 

 the sun as successively reflected from doudl :t "' Mun K' 



different distances in the heavens; but if ti ;he tJ ' cor J- 



case, it is obvious that the light thus reflected would be 

 either wholly or partly polarised, and if- were 



not incident on the clouds at the pu'......ng angle, 



the polarisation would still be ctlcettd ! ;ilx.T 



of reflections which it undergoes. l)r Brewster, 

 however, has shown, from immediate observation, tlint 

 the light of the aurora borealis has noli" of the proper- 

 ties of reflected light, and mnsi t'leTiure be direct light 

 generated in our own atmosphere. 



Mr Ronayne, Mr Cavallo, and some other authors, State of the 

 have often observed the state of the air during an au- tmosp!ii-rr 

 rora borealis, with electrical kites and thunder rods, llll " n K the 

 but they were not able to procure any indication of *j 

 electricity. On the other hand, a hissing and crackling *' 

 noise IIRS been heard by Mr Nairneand by Mr Cavallo, 

 and Canton and Volta have obtained unusual degrees 

 of electricity during the prevalence of this meteor. It 

 must be remarked, however, that neither the existence 

 or non-existence of an unusual degree of electricity in 

 the atmosphere, during an aurora Ixirealis, could be 

 considered an an argument, cither against or in favour 

 of its electrical origin ; for it will appear, from the fol- 

 lowing Table, that the phenomenon takes place at such 

 a height above the surface of the earth, that the regions 

 in which it is formed might be highly charged with elec- 

 tric matter without imparting it in an unusual degree 

 to the lower strata of the atmosphere. 



In our article AUIIORA BOREALIS we hve mentioned Ei cctr jci 

 the method of imitating that phenomena by electrical experiment 

 experiments. But the following experiment, conceived fonmit- 

 by the Abbe Bertholon, affords the best representation < in ? die 

 of the luminous columns by which the northern lights Bt "'" *- 

 are generally distinguished. Let RR, Plate CCXLV1. r< 

 Fig. 4. be the receiver of an air pump, and let a rod TT 

 be screwed into a hole E, in a crescent of metal CD, 

 whose lower surface consists of a number of angular pro- 

 jections ; let a circular segment SS, of metal, having cor- 

 r< sponding angular projections, l>e placed on the plate 

 of the air pump, then when the receiver is exhausted, 

 and the metallic shoulder A is electrified, the whole of 

 the receiver will be filled with a superb light, and co- 

 lumns of fire will dart from the angular projections in 

 the crescent, to those of the plate SS. 



The following Table contains the height of the aurora 

 borealis at various times, and according to different 

 observers. Excepting two or three numbers, the Tabk 

 is taken from Bergman. * 





See Thomson'! A**ab f I'kilotnyty, 1814, vol. iv. p. 430. 



