ELECTRICITY IN MOTION. S? 



lions are so strong, as to carry the partidos of the respective 

 bodies through an intervening medium, which is in a fluid ^tafp, 

 or even through a moist solid; nor are they intercepted in thoir 

 passage by substances, which in other cases, have the strongest 

 elective attractions for them. Alkali, sulphur, and alkaline sul- 

 phurets, are positive with respect to <he metals, and much more 

 with respect to the acids : hence they have a very strong natural 

 tendency to combine with the acids and with oxygen ; and hydro- 

 gen must also be considered as belonging to the same class with 

 the alkalies. 



Supposing now a plate of zinc to decompose a portion of water : 

 the oxygen, which has a negative property, unites with the zinc, 

 and probably tends to neutralise it, and to weaken its attractive 

 force; the hydrogen is repelled by the zinc, and carries to the 

 opposite plate of silver its natural positive electricity ; and if the 

 two plates be made to touch, the energy of the plate of zinc is 

 restored, by the electricity which it receives from the silver : and 

 it receives it the more readily, as the two metals, in any case of 

 their contact, have a tendency to become electrical, the zinc posi- 

 tively, and the silver negatively. Mr. Davy therefore considers 

 this chemical action as destroying, or at least counteracting, the 

 natural tendency of the electrical fluid to pass from the water to 

 the zinc, and from modifications of this counteraction he explains 

 the effects of galvanic combinations in all cases. Thus, in a circle 

 composed of copper, sulphuret, and iron, the fluid tends to pass 

 from the iron towards the sulphuret, and from the copper to the 

 iron, in one direction ; and iu the opposite direction from the cop. 

 per to the sulphuret, with a force which must be equal to both the 

 others, since there would otherwise be a continual motion without 

 any mechanical cause, and without any chemical change ; but the 

 action of the sulphuret on the copper tends to destroy its electro, 

 motive, or rather electrophone power, of directing the current 

 towards the sulphuret, and its combination with the sulphur makes 

 it either positively electrical, or negatively electrical in a less con- 

 siderable degree ; consequently the fluid passes, according to its 

 natural tendency, from the copper to the iron, and from the iron 

 to the sulphuiot. In a third case, when copper, an acid, and 

 water, form a circle, the natural tendency is from the acid to the 

 copper on one side, and from the acid to the water, and from the 

 nater to the copper ou tlie other ; here we must suppose the first 



