HISTORY OF GALVANISM. 89 



chemical effect is produced on the water in the in- 

 terrupted circuit. When the oxidation is pro- 

 duced by means of pure water, there is no shock, 

 although the chemical effects take place ; and 

 lastly, when either of these effects are produced, 

 the current of electricity is retarded in its passage 

 across the water in the interrupted circuit.* 



It was in the prosecution of these experiments, Discovery 

 while he was examining the effect of different t r f iL ! h c e ! Iec " 

 conducting substances placed between the plates, lumn - 

 that De Luc was led to the discovery of the 

 curious instrument, which he named the electric 

 column. It is a pile consisting of a number of 

 disks of zinc and Dutch gilt paper, placed alter- 

 nately upon each other, and included in a glass 

 tube. In order to produce any considerable effect, 

 it is necessary that the instrument should contain 

 several hundred pairs of plates ; when the number 

 amounts to 800 or 1000 it will always affect the 

 electrometer. They are made about two-thirds of 

 an inch in diameter, and are kept in their proper 

 position by rods of glass, coated with sealing wax. 

 The end of the column which is bounded by the 

 zinc plate is found to be in the state of positive 

 electricity ; that bounded by the copper plate, of 

 negative electricity .f 



Different opinions have been entertained re- Remarks 

 specting the nature of this apparatus, whether it OI 

 should be regarded as a galvanic, or simply as an 



' 



* Nicholson's Journal, xxvi. 1 16, 241. f Ibid. xxvi. 246. 



