112 ANNUAL OF SCIENTIFIC DISCOVERY. 



The beautiful phenomena of electrical Unlit in rarefied gases, as 

 exhibited in the electrical egg and Gassiot's and Geissler's vacuum- 

 tubes, afford many interesting subjects of inquiry. As the color of 

 the light is dependent on the specific nature of the gas, and as this is 

 reduced to an extreme degree of rarefaction, we have a means in 

 some cases of identifying such substances when their quantity is so 

 minute as to defy all other means of detection. With tubes of slen- 

 der bore, affording, as has been seen, a light of great intensity, we 

 may obtain a brilliant prismatic spectrum, which, as Pliicker has 

 shown, is marked in each case by some characteristic peculiarity ; and 

 with the same arrangement we are able to trace the chemical changes 

 which the enclosed gas or vapor undergoes while subjected to the 

 electrical action. 



Perhaps the most important observations in this connection are 

 those recently made by Gassiot, whose ingenious application of the 

 absorbent power of potassa has enabled him to approximate more 

 nearly to an absolute vacuum than any previous experimenter. In a 

 tube thus prepared, he has found that the gas may be so excessively 

 rarefied as to be unable to transmit the current, at this stage ceasing 

 to be luminous. We may therefore conclude that the old notion of a 

 vacuum being a good conductor, which was founded on the electric 

 illumination of the Torricellian space, is entirely erroneous, and that 

 in all cases conduction is dependent on the presence of some form of 

 ponderable matter. 



Adverting to the new evidences which these and other recent ex- 

 periments afforded of the electrical character of the Aurora, Profes- 

 sor Rogers called attention to the actionof a magnet on the Metric 

 light, and more particularly to its power of arranging the illumination 

 in meridional bands, and impressing upon them a movement of rota- 

 tion, as exhibited in De la Rive' s experiment ; and mentioned the in- 

 genious suggestion of Grove, that the height of the aurora above the 

 earth's surface might perhaps be inferred from a knowledge of the 

 degree of rarefaction at which like luminous effects were obtained in 

 the vacuum-tubes. 



In connection with the fluorescent influence of the electric light, 

 he mentioned the fact, that during the brilliant aurgral displays of 

 August and September, 1859, he found that a solution of sulphate 

 of quinine showed its characteristic fluorescence quite distinctly 

 when exposed during the height of the illumination. 



Prof. Rogers stated that he had obtained a strong photographic 

 picture on a collodion plate, from an electric flash, in less than 

 half a second of time ; and adopting the estimates of Wheatstone 

 for the time an electric spark requires for transmission, a photo- 

 graphic impression had been obtained from an electric light less than 

 of a second in duration. 



10000 



ELECTRO-CHEMICAL COLORATION. 



In a memoir recently presented to the French Academy of Sciences 

 by M. Becquerel, on electro-chemical coloration, the author stated, 

 that Priestley was the first to obtain colored rings by means of electri- 

 city, by receiving strong charges from a battery, with surface of 



