on various Phenomena of Induction. 279 



ductor in order to obtain the appearance of the electric glow 

 (lueur) ; it is observable without interruption as soon as the 

 plate is turned rather rapidly, on placing the egg at a proper 

 distance. 



43. Upon the glass plate of the air-pump I spread a leaf of 

 the same nature, on which I insulated a brass button of 0"^'04<8 

 diameter. This ball was covered with a glass funnel reversed, 

 in the neck of which I cemented a stem, also of brass, of C^'OOi 

 thickness, and terminated below by a ball 0™*024< in diameter. 

 Between the two balls there was about O'^'OIO interval. The 

 funnel was itself placed under a glass bell, bearing a leather 

 valve and a stem which descended to C^'OS from the prece- 

 ding. After exhaustion of the air, the same phaenomena 

 appeared, the plate (secondary) employed being placed in 

 communication with the ground or insulated on a glass plate. 



44. Analogous results were obtained on replacing the bell 

 furnished with the metallic stem, projecting exteriorly, by an 

 attached glass bell ; the balls were then in the most perfect 

 state of insulation and in the most perfect vacuum. I em- 

 ployed a double-cylinder air-pump by Babinet. 



45. I have thus proved, that on placing an electrical egg 

 near a Leyden jar of mean dimensions and charged to satura- 

 tion, there is no luminous spark between the charcoal points, 

 when the electrical explosion between the two armatures takes 

 place instantaneously, whilst a very brilliant one is visible 

 during the entire duration of a prolonged discharge, such as 

 is obtained by means of a point. I believe this observation is 

 new. 



B. Dynamical Induction. 



46. The small helix was placed on the plate of the air- 

 pump. By means of very fine copper wires covered with silk, 

 a communication was made between the inductor wire and 

 piles of four or six pairs, and between the induced wire and 

 the hydro-electrical rheometer. These conducting wires, 

 plunged in the grease with which the broad surface of contact 

 of the bell-glass with the plate attached was covered, did not 

 at all prevent a very good vacuum from being formed. 



47. The deviation of the needle caused by the induced cur- 

 rent was found to be independent of the quantity of gas re-ad- 

 mitted into the receiver. The observations -were repeated at 

 different times for differences of 0™'025 height of the column 

 of mercury measuring the elastic tension, from a vacuum up 

 to the ordinary atmospheric pressure, Qi^'125. 



