408 Intelligence and Miscellaneous Articles. 



duced under the influence of a toothed disk of india-rubber previ- 

 ously electrified. We remark, in short, that the flash of the illumi- 

 nation increases with the velocity of the disk. This circumstance 

 is but little favourable to the hypothesis according to which the in- 

 fluence would be exercised across dielectrics by a polarization of 

 successive layers ; it would be necessary in that case that the polar- 

 ization should be instantaneous, and we cannot see in what the 

 difference between insulating bodies and conductors would consist. 



III. Tubes filled with rarefied gases and provided with metallic 

 wires sealed at the ends like Geissler's tubes, but terminated ex- 

 ternally by knobs to prevent the wires from acting like points, may 

 be applied with advantage to demonstrate the movements of electricity 

 to which the influence gives rise, especially those of the return shock. 

 I have executed these experiments ; but the credit of them is due to 

 M. G. Govi, of Turin, who has very ingeniously employed this means 

 of demonstration in the place of metallic conductors armed with 

 pendulums, of the electroscopic frog, and of the other contrivances 

 usually employed in this part of the study of electricity *. These 

 luminous conductors have also been made use of by him to exhibit 

 the phenomena of induction of different orders by interposing them 

 in long metallic circuits. 



IV. In the course of the experiments which I have had occasion 

 to make with rarefied gases, I have remarked that the glass was 

 charged by the intervention of gaseous conductors with the same 

 facility as by means of metallic conductors. I have thus been led 

 to construct a Leyden jar in which the metallic coatings are replaced 

 by rarefied gas : it is composed of a closed primary tube enveloped by 

 a second, to which it is fused ; each of the tubes is provided with a 

 platinum wire ; a vacuum is created in them to the extent of about 3 

 millims. Such a system is charged with a Leyden jar of the same 

 dimensions ; the residues in it seem to be less abundant than in ordi- 

 nary jars ; but this question, in order to be fully solved, requires 

 more numerous experiments. 



In fine, rarefied gases behave precisely as metallic conductors. It 

 is to be remarked that such a medium formed into a point acts just 

 like a metal of the same shape, and manifests the same effects of 

 tension, to such an extent that, in the glass vessels intended to con- 

 tain gases with a view to the experiments here treated of, it is neces- 

 sary to avoid all such tapering of the tubes as would give to the 

 interior surface the form of an acute point. If this circumstance 

 does happen, and the interior gas is strongly electrified, we often see 

 the electricity strike out for itself a passnge through the glass at that 

 place ; and if the glass be too thick, the electricity, in place of 

 opening a direct path for itself, cracks off the little button of melted 

 glass which generally terminates the tapering ends closed by the 

 blowpipe. — Comptes Rendvs, Ma}^ 31, 1869. 



* Gazette officielle du Royaumedltalie, No. 49, 1865. 



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