ELECTRICITY. 121 ' 



bard, the mere effect of permanent currents of natural electricity, established 

 and maintained upon its surface by various physical causes ; that, as a violent 

 current, like that which attends the exhibition of lightning, produces instanta- 

 neous and powerful magnetism in substances capable of receiving that quality, 

 so may a more gentle, regular, and constant circulation of the electric fluid 

 upon the earth impress the same virtue on all such bodies as are capable of 

 it. Observation proves that a vast quantity of this fluid circulates between 

 different parts of the atmosphere in storms ; that a quantity not inconsiderable 

 circulates in the time of ordinary rain ; and that even when the weather is se- 

 rene arid the heavens unclouded, some quantity is still observable. " Of such 

 fluid, thus ever present," observes Beccaria, " I think that so'me portion is con- 

 stantly passing through all bodies situate on the earth, especially those which 

 are metallic and ferruginous ; and I imagine it must be those currents which 

 impress on fire-irons, and other similar things, the power which they are known 

 to acquire of directing themselves according to the magnetic meridian when 

 they are properly balanced."* 



He observed, that to say we are insensible to this current around us, is no 

 good argument against its existence ; for that its uniformity, constancy, and 

 universality, would necessarily render it imperceptible, since all bodies must 

 partake of it in common. His hypothesis to account for the variation and dip 

 is not the least remarkable part of this extraordinary anticipation. He consid- 

 ers that the electro-magnetic currents have not all a pommon centre, but may 

 have several situate in our northern hemisphere. The aberration of their com- 

 mon centre from the true terrestrial pole may probably be the cause of the 

 variation of the compass. The periodical change to which the position of this 

 common centre is subject would correspond with and cause the periodical 

 change of that variation, and the obliquity of these currents may be the cause 

 of the dip.f 



That the anticipation of the fundamental principle of electro-magnetism, and 

 terrestrial magnetism, should have been complete in all its details, could scarce- 

 ly have happened at that epoch without something approaching to inspiration ; 

 but it will be readily admitted that these guesses of Beccaria, when compared 

 with the discovery of Orested and the theory of Ampere, form one of the most 

 striking episodes in the history of science. 



The analogy between lightning and the electric spark, arising from the pe- 

 culiar noise or explosion with which each was attended, had been noticed by 

 many electricians. Beccaria. however, investigated and demonstrated its cause, ; 

 by showing that it proceeded from a pulsation produced in the air by the sudden 

 displacement of that portion of it through which the electric fluid passes. This 

 displacement being transmitted through the atmosphere in exactly the same 

 manner as vibrations are produced by a sonorous body, the sound accompany- 

 ing an electric discharge, and the thunder which attends the atmospheric elec- 



* " Di tale fuoco, io penso che alcana parte perpetuamente discorra per tutti i corpi situati sopra 

 la terra, massimamente per i metallic! e ferigni. Penso che esso sia, il quale attraversando le padelle, 

 Is aiolle, le palette ed altri si fatti bislnnghi ferri, i quali d'ordinario pendono o posano verticalmente, j 

 imprima loro la virtil di situarsi nella meridiana rnagnetica, allora che sono convenientemente bili- > 

 cati." Lettere, p. 266. 



t " Questa sistematica elettrico-magnetica circolazione, secondp me, non procederebbe da an solo 

 panto setteiHrionale, ma avrebbe infinite sorgenti in divers! punti del nostro settentrionale emisfero, 

 forse successivamente. pill folte ne luoghi piu vicini ad alcun panto settentrionale ; e la frequenza, la 

 posizione, o piuttosto la direzione del corso loro mi si rappresenterebbono dalla posizione, frequen- 

 za, e diverzione, con che si dispongono intorno alii emisferi di una sferica calamita le ordinatissime 

 fiize della limitura di ferro. E giasta ana tale ipotesi, 1'aberrazione del centro comane di tutte le 

 varie sorgenti, che estenderebbono la loro azione ad una data ragione, dal \ero punto settentrionale 

 mi spiegherebbe 1'aberrazione della calaraita ; il periodo di quella aberrazione mi spiegherebbe il 

 periodo di questa declinazione ; i'obbliquita, con che qaelle sorgenti spiccierebbono da terra, e si 

 direggerebbono verso mezzo di, mi spiegherebbe e la inclinazione degli aghi, e la particolare fa- 

 ciliti con che si calamitano i ferri si fattamente inclinati." Lettere, p. 268. 



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