124 ANNUAL OF SCIENTIFIC DISCOVERY. 



we ought, by the theory, to get no stria. If an interruption be made in the 

 secondary current, in addition to that formed by the rarefied medium, and 

 this interruption be made of the full extent which the spark will pass, there 

 arc, as a general rule, no striae in the rarefied medium, while the same 

 vacuum tube shows the striae well if there be no such break or interruption. 

 The experiment was shown by a large vacuum cylinder (16 inches by 4) 

 of Mr. Gassiot, and his micrometer-electrometer; this tube showed numer- 

 ous broad and perfectly distinct bands when the points of the micrometer 

 were in contact; but when they were separated to the fullest extent that 

 would allow sparks to pass, not the slightest symptom of bands or stria) 

 was perceptible; the whole cylinder was filled with a uniform lambent 

 flame. AVith a spark from the prime conductor of the electrical machine, 

 the striae do not appear in tubes which show them well with the Ruhmkorff 

 coil; occasionally, and in rare instances, striae may be seen Avith sparks from 

 the electrical machine, but not as far, as Mr. Grove has observed, when the 

 spark is unquestionably single. All this is in favor of the theory given 

 above; but without regarding that as conclusive, or as proved rationale, it is 

 clearly demonstrated by the above experiments that the identical vacuum 

 tubes which show the striae with certain modes of producing the discharge, 

 do not show them with other modes, and that therefore the striae are not a 

 necessary condition of the discharge itself in highly attenuated media, but 

 depend on the mode of its production. 



The study of the electrical discharge in vacua is of the utmost importance 

 in reference to the theories of electricity, and probably will assist much 

 towards the proper conception of other modes of force, or, as they are 

 termed, imponderables, heat, light, etc. 



The experiments of Walsh and Morgan, corroborated as they now are by 

 that of Mr. Gassiot, show that, although the tz-ansmission of electricity 

 across gaseous media is aided b}* refraction of the medium up to a certain 

 degree, yet that a degree of attenuation may be reached at which the trans- 

 mission ceases, at all events for a given distance between the terminals and 

 given intensity of electrical charge. Whether, having reached this point, 

 a reduction of the space to be traversed, or an increase of intensity in elec- 

 tricity, or both, would again enable the electricity to pass, is not quite clear, 

 though there is reason to believe that it would, and the increased inten- 

 sity of electricity would probably be again stopped by a further improve- 

 ment in the vacuum, and so on. But the experiments go far to prove that 

 ordinary matter is requisite for the transmission of electricity, and that if 

 space could exist void of matter, then there would be no electricity ; thus 

 supporting the views advocated by Mr. Grove and some others, that elec- 

 tricity is an affection or mode of motion of ordinary matter. 



The non-transmission of electricity, by very highly attenuated gas, may 

 also afford much assistance to the theory of the aurora borealis, a phenome- 

 non, the appearance of which, the regions where it is seen, its effect on the 

 magnet, and other considerations, have led to the universal belief that it is 

 electrical. 



The experimental result that a certain degree of attenuation of air forms 

 a good conductor, or easy path for the electrical force, while either a greater 

 or less degree of density offers more resistance, and this increasing towards 

 either extremity of density or rarefaction, shows, that if there be currents of 

 electricity circulating to or from the polar regions of the earth, the return of 

 which, as is generally believed, gives rise to the beautiful phenomena of the 



