200 Mr. Armstrong's Account of a 



4th. By scattering some particles of dust upon the surface 

 of the water, I soon perceived by their motions that there 

 were two opposite currents passing between the glasses, which, 

 judging from the action upon the silk thread in the centre of 

 the column, as well as from other less striking indications, I 

 concluded to be concentric, the inner one flowing from nega- 

 tive to positive, and the outer one from positive to negative. 

 Sometimes the outer current, or that which I assumed to be 

 such, was not carried over into the negative glass, but trickled 

 down the outside of the positive one ; and then the water, in- 

 stead of accumulating as before in the negative glass, dimi- 

 nished both in it and the positive glass. 



5th. After many unsuccessful attempts, I succeeded in causing 

 the water to pass between the glasses, without the intervention 

 of the thread, for a period of several minutes ; at the end of 

 which time I could not perceive that any material variation 

 had taken place in the quantity of water contained in either 

 glass. It appeared therefore that the two currents were nearly, 

 if not exactly equal, when the inner one was not retarded by 

 the friction of the thread. 



As you are so much more competent than I am to draw 

 conclusions from this curious experiment, I shall not ad- 

 vance any opinion upon the subject, further than by observing 

 that it appears to me to be eminently calculated to elucidate 

 the nature of the electric current. 



It is proper to state that I found it essential to the success 

 of this experiment, that the water in the glasses should be 

 perfectly pure. The slightest contamination caused the water 

 to boil upon the thread, instead of passing between the glasses 

 in the manner I have described, and the instant the thread 

 became nearly dry, it was destroyed by the heat elicited by the 

 current of electricity. To ensure success it was necessary to 

 use water distilled in glass vessels, for I found that the common 

 distilled water which I obtained at the chemists' shops, was in 

 general insufficiently pure for the purpose. 



Amongst various other cases of electro-chemical action ef- 

 fected by this machine, I may instance the coating of a small 

 silver coin with copper, by attaching it to a platina wire which 

 formed the negative pole in a solution of sulphate of copper, 

 but a long-continued action of the machine was required be- 

 fore this was accomplished. I may also mention the decom- 

 position of iodide of potassium to such an extent as to colour 

 a deep blue wine-glass-full of the solution in a very short time, 

 when starch and a few drops of hydrochloric acid were present. 

 When the hydrochloric acid was omitted, the mixture in ge- 

 neral changed to an amber instead of a blue colour. 



A magnetic needle, suspended by a fibre of silk between 



