DISCOURSE OF W. B. TAYLOR: NOTES. 397 



water by electric shocks, that both descriptions of gases are exhibited 

 at both electrodes.' " * 



Seventeen years after Henry's experimental determination, Mr. 

 W. Feddersen, in 1859, observed the oscillatory nature of the elec- 

 trical discharge, by employing the revolving mirror of Wheatstone, 

 as first suggested by Sir William Thomson. f 



It is remarkable however that very early in the century, the 

 return discharge of electricity appears to have been distinctly noted. 

 In Gilbert's Annalen for 1806, the phenomenon of a "back-stroke" 

 is spoken of as being " not uncommon in thunder-storms." J And 

 twenty years before the conjecture by Helmholtz, or in 1827, the 

 same suspicion or rather conviction of an oscillatory discharge was 

 distinctly expressed by Felix Savary, who perplexed by the irregu- 

 larity of magnetization in small needles, when effected by the Ley- 

 den jar, thus comments on the problem : 



"An electrical discharge is a phenomenon of motion. Is this 

 motion a translation of matter continuous in a fixed direction? 

 If so, the alternations of opposite magnetisms observed at various 

 distances from a rectilinear conductor, or in. a helix for gradually 

 increasing discharges, would be due solely to the mutual re-actions 

 of the magnetic particles in the steel needles. The manner in which 

 the behavior of a wire changes with its length, appears to me to 

 exclude this supposition. Does the electric flow during a discharge 

 consist on the contrary of a series of oscillations transmitted from 

 the wire to the surrounding mediums, and speedily enfeebled by 

 resistances which increase rapidly with the absolute velocity of the 

 agitated particles? All the phenomena lead to this hypothesis; 

 which assumes that not only the intensity, but the direction of the 

 magnetism, depends on the laws according to which the minute 

 motions die away in the wire, in the medium surrounding it, and in 

 the substance which receives and preserves the magnetism. The 

 oscillations in the wire would have an absolute velocity so much the 

 less, and would subside so much the more rapidly, accordingly as 

 the wire were longer, as it were finer, and as the resistance belong- 

 ing to its constitution were greater. It may thus be explained how 

 there is for a rectilinear conductor and a given discharge, a length 

 of wire which will produce the strongest magnetization; if the 



* Quoted from a memoir "On the Conservation of Force," by Dr. H. Helm- 

 holtz. Read before the Physical Society of Berlin, on the 23d of July, 1847. The 

 memoir was translated by Dr. J. Tyndall, and published in his selection of "Sci- 

 entific Memoirs," London, 1853, vol. i. p. 143. This interesting collection of foreign 

 papers forms a continuation of Taylor's "Scientific Memoirs," in five volumes. 



f Poggendorflf's Annalen der Physik, 1859, vol. cviii. p. 499. 



I Gilbert's Annalen dei- Physik, 1806, vol. xxiv. p. .351. 



