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medium in which they exist, attracting the fluid of the contrary name, and re- 

 pelling the fluid of the same name. The atoms are therefore considered as 

 strictly analogous to the Leyden jar ; the internal charge representing the 

 natural electricity of the atom, and the external that which is drawn from the 

 surrounding medium. If a combination is formed between an electro-positive 

 and an electro-negative body, a discharge takes place ; the atoms dismiss their 

 external charge, and rush into union in virtue of the reciprocal attraction of 

 their opposite natural electricities. The atmospheres of the atoms, as well as 

 the atoms themselves, are combined ; but, as the atoms cannot emerge from 

 ( them, their electricities act on those of their atmospheres, exerting attractions 

 and repulsions, so as to produce electrical phenomena the reverse of those 

 which attended their combination. 



The zinc plates of a Voltaic apparatus, being subject to continual oxydation, 

 are at length so reduced in thickness, as to render it necessary to replace 

 them by new ones. This gradual wear of the pile by use rendered it desira- 

 ble to seek for means of constructing a pile composed of solid elements only ; 

 a project, however, which could only be entertained by those who conceived 

 that chemical action was merely incidental, and not essential, to the develop- 

 ment of Voltaic electricity. Although the high probability, if not the certainty, 

 that chemical action is indispensable, must render abortive all attempts at the 

 discovery of a dry pile, such researches have nevertheless been attended with 

 some advantage. 



The term dry pile was intended originally to express a Voltaic pile, of which 

 all the elements were solid ; and the advantages of such an instrument, if it 

 could be discovered, were so apparent, that the attention of electricians was di- 

 rected to it at an early period in the history of Voltaic discovery. If a pile 

 composed of solid elements (thought they) could but be discovered, neither 

 evaporation nor chemical action could take place ; the electricity due to the 

 contact of heterogeneous bodies, according to Volta's theory, would be contin- 

 ually evolved ; and as the bodies evolving it would suffer no change, the quan- 

 tity and intensity of the electricity supplied by the instrument would be abso- 

 lutely uniform and invariable. In 1803, MM. Hachette and Desormes substi- 

 tuted starch for the liquid in the common pile ; and, in 1809, De Luc invented 

 a pile apparently free from any liquid element. This apparatus consisted of a 

 column formed of alternate disks of zinc and paper gilt on one side, the gilt 

 sides of the paper disks being all turned in one direction. This was in reality 

 not a dry pile ; the paper imbibed and retained moisture enough to give a feeble 

 activity to the apparatus. 



De Luc's pile was improved by Zamboni in 1812. He rejected the disks 

 of zinc, and composed the pile of disks of paper only, one surface being tinned, 

 and the other coated thinly with the peroxide of manganese, brushed with a 

 mixture of flour and milk ; or gilt or silver paper may be used, the metallic 

 surface being wetted with a saturated solution of the sulphate of zinc, on 

 which, when dry, the peroxide of manganese in powder, may be spread. 

 Several leaves of paper thus prepared are placed one upon the other, and cut 

 into the required form by a circular cutter. As many disks are thus formed by 

 one operation as there are leaves of paper superposed ; and these being after- 

 ward laid one upon the other, the pile is formed. Thi's pile is usually placed j 

 in a hollow cylinder, of the same internal diameter. The paper disks are forced ) 

 into close contact by pressure produced by screws. 



Although, by the aid of a condenser, the electricity evolved in these piles 

 may be rendered sensible, and sparks may even be obtained, the power is in- 

 comparably more feeble than that of the common pile, even ia its most ineffi- 

 cient state. It is found that by increasing beyond a certain limit the number j 



