ELECTRICAL EXPERIMENTS ON GLASS. Qj 



©n the contrary saturates itself infinitely more quickly : in sooner saturat- 

 a little time it discharges on itself, notwithstanding the lit- ^^^ Jj^ 

 tie extent of the coatings. We ascribe the anomaly of* these 

 two different kinds of glass to different fluxes. The Ger- 

 man glass contains more metallic oxide, the common more 

 saline matter. If this inference be just, the English flint Flint glass, 

 glass should be like a sponge to the fluid; and if it were 

 possible to find large squares coloured with metals, these 

 perhaps would furnish us with other facts. 



It must be observed, that, notwithstanding the German German glass, 

 glass admits this passage, a large mass will not pass, unless 

 it be attracted in the manner related in a former letter. 

 This is why we see a reflux toward the machine. The fol- 

 lowing experiment will in some degree account for this. 



I charge a glass electrophorus, placed on an insulating Experiment, 

 stand, the lower coating of which is as extensive within an 

 inch as the glass, and stop the machine the moment the 

 sparks announce an approaching spontaneous discharge : if 

 in this state I cut off the communication with the ground, 

 and take the cap from the upper surface, the whole charge 

 will remain adhering to the glass; and on touching it a 

 prickling sensation will be felt, and something like an ig- 

 neous vapour. On extinguishing the light it is visible, 

 particularly if you approach the edge; but the fluid be- The fluid may 



comes absolutely luminous, if you blow lightly on the sur- be blown to ~. 

 J „ n 11 ■ • i wardmalunu- 



face: then a wave ot nre traverses the glass, to join the nous wave 



fluid accumulated on the other side between the glass and 

 the metallic coating. What is particularly remarkable, two of two colours, 

 colours may be distinguished in the fluid, the lower being 

 whiter and more vivid. This phenomenon takes place if 

 the communication be suffered to remain : the wave of fire, 

 which flows from the part blown upon toward the lower sur- 

 face is stronger, but it does not continue so long. This The electric 

 experiment gives rise to the question, whether all the in- Q Und ° r c * m " 

 gredients pass through the substance of the glass, or whe- 

 ther the difference of action is to be ascribed to the state of 

 the glass alone. I believe it is this modification, which the 

 electric matter itself appears to undergo, that constitutes 

 the opposite states, which every natural philosopher endea- 

 vours to explain according to the mode in which he views 



F 2 them; 



