to account for the Phcenomena of Electricity. i)45 



possible, the filament should have absorbed as much fluid as 

 had been deficient in it, and so would be brought to the natural 

 etate. 



If the foregoing reasonings be just, it would appear that th* 

 second principle of the theory does not accord with the phae- 

 nomena which it is intended to explain, and that all arguments 

 founded on it are contradictory to facts and amongst tliemselves. 

 The third principle is next to be considered. 



3. The impermeability of glass is a position which seems in- 

 compatible with the doctrine of plus and minus. If a plane of 

 glass be made negative it should remain so for ever if electricity 

 cannot return mto it. But the previous question occurs, How 

 did the natural portion get out, if glass refuse a passage to it ? 

 This perhaps cannot be answered without a multiplicity of hy- 

 potheses. 



As to the fact, whether or not glass is actually impermeable, 

 many experiments have been made, but they all appear to be of 

 doubtful force, and may be explained in some manner without 

 supposing that electricity passed through. I am not aware that 

 this objection can apply to the following. 



Having procured a sphere of very thin glass about 2^ inche» 

 diameter, tlunished with a neck 9 inches long, I coated its lower 

 hemisphere outside with tin-foil, and poured into it mercury al- 

 most as high as the coating. A moveable wire proceeding from 

 the conductor of an electric machine dipped down into the mer- 

 cury . The flask was charged through this wire, the latter was 

 withdrawn, and the neck was sealed, by a blow-pipe, so far as 

 barely to admit the ])assage of tlie wire. I now found that the 

 flask was as capable of giving a shock as before, proving that 

 the heat used in sealing did not draw out the charge. The 

 flask was again strongly charged, and its neck totally sealed. 

 After an immersion of 14 days in water, the neck was cut off, 

 the glass was completely dried, and a wire was pushed down 

 into the mercury. A shock not exceeding 1 -20th of the force 

 of the original charge was the result : which shows that 19-20ths 

 must have left the glass. The experiment was repeated with 

 numerous precautions : the sphere was exposed to the air foF 

 six months: and at the end of this time not a trace of electricity 

 could be detected when the neck was cut. 



Dr. Franklin had made some trials with a similar object in 

 view: but he was led to a conclusion directly the reverse of 

 mine. Perhaps the gi'eatcr thickness of the glass in his ex- 

 periment, may reconcile the results. 



Although it ajjpears that glass is in the strict sense of the 

 word, permeable to electricity, yet the fluid passes through it 

 with so much dilliculty and so slowly that Franklin's position 



might 



