Metallic Bodies by Voltaic Electricity. 215 



of the battery, in three or four portions, both when separate and 

 combined. Thus if the points of elevation of the fluid corre- 

 spond with the respective quantities of metal in action, or very 

 nearly so, supposing the combination arranged as a single pair of 

 plates, we may fairly presume that the instrument will indicate 

 any trifling variation of power upon the whole. It is requisite 

 also to observe, that the steadiness of the fluid at a given point, 

 was found to depend exclusively on the strength of the acid so- 

 lution and state of the battery. When the zinc is moderately 

 clean, and the action somewhat brisk, the power of the battery 

 to maintain the fluid for a considerable time, at a constant alti- 

 tude, is very decisive ; on the contrary, when a weak acid is em- 

 ployed, or the zinc is loaded with oxide, then the effect is always 

 more or less evanescent, being greatest at the instant of com- 

 pleting the circuit, after which the fluid sinks gradually along 

 the scale, until it reaches some point at which the action of the 

 battery may be considered constant ; whilst, in other cases, no 

 stationary point can be obtained, and the fluid sinks gradually to 

 zero. When, however, the battery is in a good state for experi- 

 ment, and the acid sufficiently strong, the fluid will be observed 

 to rise steadily, and remain stationary at some given point of the 

 scale. The circuit, however, should in all cases be made with 

 very large copper wires, of at least one-fourth of an inch in dia- 

 meter, and the contacts made good and perfect, in the usual 

 way, by means of mercury. 



15. The utility of the instrument, with some of the attendant 

 circumstances, having been thus far investigated, I endeavoured 

 to apply it, in a variety of instances, to the further elucidation of 

 the phenomena of voltaic action, some few of which it may not 

 be unimportant to notice. 



(h) The zinc and copper plate, already described (4), Fig. 1, 

 being exposed to the action of a dilute acid, and the resulting 

 effect on the electrometer noted ; a second and similar plate of 



E e2 



