1859.] and its stratified Appearance in Rarefied Media, ' 7 



more particularly by Mr. Gassiot; and the extent of knowledge we 

 have acquired upon this still mysterious phenomenon was now discussed 

 and illustrated. 



In the vapour of phosphorus the striae generally exhibit themselves 

 like narrow ruled lines, about 0*05 inch diameter, transverse to the 

 line of discharge ; but with certain precautions they become wider and 

 assume a conical form, somewhat resembling the whalebone snakes 

 made as a toy for children. Mr. Gassiot has used most carefully pre- 

 pared Torricellian vacua, and has also, in conjunction with Dr. 

 Frankland, obtained excellent vacua, by filling tubes containing sticks 

 of caustic potass with carbonic acid, exhausting them by the air-pump, 

 and allowing the residual gas to be absorbed by the potass. 



The following is a summary of the effects produced by the electric 

 discharge through these vacua. 



If the vacuum be equal to that generally obtained by an ordinary 

 air-pump, no stratifications are perceptible ; a diffused lambent light 

 fills the tube : in a tube in which the rarefaction is carried a step 

 further, narrow striae are perceptible, like those first described in the 

 phosphorus vapour experiment. A step further in rarefaction increases 

 the breadth of the bands ; next we get the conical or cup-shaped form ; 

 and then, the rarefaction being still higher, we get a series of luminous 

 cylinders of an inch or so in depth, with narrow divisions between 

 them. Lastly, with the best vacua which have been obtained, there is 

 neither discharge, light, or conduction.* The fact of non-conduction 

 by a very good Torricellian vacuum was first noticed by Walsh, sub- 

 sequently carefully experimented on by Morgan (Philosophical Trans- 

 actions, 1785), and subsequently by Davy (1822) ; the latter did not 

 obtain an entire non-conduction, but a considerable diminution both 

 of light and conducting power. 



From these repeated experiments it may fairly be considered as 

 proved, that in vacuo, or in media rarefied beyond a certain point, 

 electricity will not be conducted, or more correctly speaking, trans- 

 mitted ; an extremely important result in its bearing on the theories of 

 electricity. 



The gradual widening of the strata, as the rarefaction proceeds, is 

 in favour of the phenomena of stratification being due to mechanical 

 impulses of the attenuated medium, and appears to support the follow- 

 ing rationale of the phenomenon given by Mr. Grove ; who does not 

 advance it as conclusive, but only as an approximation to a theory 

 to be sifted by further experiments. When the battery contact is 

 broken, there is generated the well-known induced current in the 

 secondary wire in the same direction as the original battery current, to 



* The production of vacua by carbonic acid, and the increasing breadth of the 

 stratifications with increased rarefaction, was communicated by Mr. Gassiot in a 

 paper, read to the Royal Society, Jan. 13, 1859. I incline to think that oxy- 

 hydrogen gas, with potash, might give a better vacuum than carbonic acid, as 

 the last residual portions of tlie gas would be slowly combined by the discharge, 

 and the water so formed absorbed by the potash. — W. K. G. 



