306 Royal Society .— 



charge when taken from the terminals of a Ruhmlcorff's induction- 

 coil in the vapour of phosphorus, and in highly attenuated gases, 

 first noticed by iNlr. Grove (Phil. Trans. Part I. 18;) 2, and Phil. 

 Mag., Dec. 1852). Having witnessed the experiments of Mr. 

 Grove, Mr. Gassiot in the same year examined the discharge in a 

 barometrical vacuum in which the mercury had been carefully boiled, 

 but he could not obtain au}' signs of stratification. These experi- 

 ments were subsequently repeated by several continental electricians, 

 who all describe the induction-discharge in a barometrical vacuum as 

 intensely white, and filling the whole tube without stratification. 



After alluding to the experiments of the Rev. Dr. Robinson (Proc. 

 R. I. Acad., Dec. 185(3), and to some recent improvements in the 

 construction of the induction-coil, the author proceeds to describe 

 apparatus which he had constructed for the more careful examination 

 of the character of the induction-discharge. His first experiments 

 were made on glass tubes about 1 inches long, in which the mer- 

 cury could be lowered or raised to any required level by means of the 

 air-pump. He also experimented with barometrical vacuums ob- 

 tained by inverting a tube of about 44 inches in length, filled with 

 boiled mercury, over a vessel containing that metal, and then sealing 

 the tube 2 or 3 inches above the barometrical height. 



The results obtained by tliese methods having been found un- 

 satisfactory, the author had recourse to that first suggested by Mr. 

 Welsh (Phil. Trans. 185G, p. 507), by which that gentleman con- 

 structed the large barometer at the Kew Observatory. Following 

 out the principles indicated by Mr. Welsh, by carefully removing all 

 trace of moisture, and thoroughly cleaning the tubes before intro- 

 ducing the mercury, the author succeeded in obtaining Torricellian 

 vacuums which exhibit the stratifications in a uniform and very 

 marked manner. 



The sealed tubes generally used by Mr. Gassiot are then described. 

 They are made of the usual glass tubing, about an inch internal 

 diameter, and of the form fig. 1 . 



They vary from 10 to 38 inches in length. In the latter case the 

 platinum wires a b are about 32 inches apart. One tube is de- 

 scribed 5 feet 3 inches in length, with wires 4 feet 9 inches apart. 



With a tube prepared on Mr. Welsh's principle, and the usual- 

 sized Ruhmkorif's induction-coil excited by a single cell of Grove's 

 nitric acid batter}', with or without a condenser, the phenomena of 

 the stratified discharge can be seen and examined with ease, and 

 without the ti'ouble and uncertain manipulation of an air-pump, or 

 the employment of phosphorous or other vapours. 



If the discharges are made in one direction, a black deposit takes 

 })lace on the sides of the tube nearest the negative terminal. This 

 deposit is platinum in a state of minute division emanating from the 

 wire, which becomes black and rough as if corroded. The minute 

 particles of platinum are deposited in a lateral direction from the 

 negative wire, and consequently in a different manner from what is 

 described as occurring in the voltaic arc, so that the luminous ap- 



