255 



one in the liquid, also two cases occur : 1 . With pure mercury, 

 the motion is negative in all liquids acid, alkaline, or neutral; 

 and, 2. With mercury containing a small quantity of an electro- 

 positive substance imparted to it by reversing the connexions of the 

 wires for a few moments, a temporary and strong positive flow is 

 produced in certain liquids and not in certain others and these 

 liquids are almost precisely the reverse of those named under B, 2. 



The general influence of electro-positive substances dissolved in 

 the globule is in all classes of cases to produce a positive flow, and 

 of electro-negative substances to produce a negative motion; and 

 the influence of electro-positive substances dissolved in the liquid 

 is, in cases of A only, to produce a positive flow, and of electro- 

 negative substances to produce a negative flow. 



4/. The primary motions of the liquid and metal are, in all cases, 

 wholly at their surfaces of mutual contact ; whilst the movements 

 observed are only secondary effects, useful in enabling us to infer 

 the direction of the original motions : the masses of liquid and 

 metal serve merely as conductors of the electricity, and as stores of 

 material for supplying the acting surfaces. The movements obtained 

 are singularly symmetrical, probably in consequence of their essen- 

 tially dual or polar character. 



48. The essential nature or principle of the movements appears 

 to be electro-chemical motion, i. e. definite motion directly produced 

 by electro-chemical action. 



49. To illustrate the action, I have constructed an apparatus 

 consisting of two pairs of electrodes of platinum foil and mercury, 

 suspended at opposite ends of two copper wires upon a central pivot, 

 and rotating in an annular channel filled with dilute sulphuric acid ; 

 but the power was too feeble to produce revolution of the necessary 

 moveable parts : it was not more than sufficient to produce a manifest 

 tendency to motion. 



In conclusion, I beg leave to suggest a trial of the sudden starts of 

 the mercury by momentary currents as signals in electro-telegraphic 

 apparatus. 



