216 Mr W. S. HARRIS on the Heat excited in 



copper, previously placed on the other side of the zinc, was 

 connected with the former, so as to double the quantity of 

 copper. In this case, the effect on the electrometer, as might 

 have been anticipated, was very considerably increased ; it was, 

 in almost every instance, at the time of making the contact, 

 at least doubled. That a considerable increase of power is ob- 

 tained by exposing both surfaces of the zinc to the influence of 

 copper plates is already well known. It is in short the principle 

 of the Wollaston arrangement of the voltaic series. But it is not 

 perhaps so well known, that a further increase of copper, with a 

 single plate of zinc, is also accompanied by a still further increase 

 of power. Thus when the number of plates of copper were qua- 

 drupled and connected, the power of the combination was great- 

 ly augmented. It appeared, from the few trials made, to be 

 principally limited by the increased distance from the zinc plate 

 at which the external plates of copper were necessarily placed. 



16. With a view of investigating the relation of the con- 

 ducting power to the quantity of metal, as also the conducting 

 powers of different metals, I resorted to an arrangement similar 

 to that represented in Fig. 3, in which the given metal mn, the 

 subject of experiment was drawn into wire, and caused to trans- 

 mit a given accumulation, in a cool fluid medium, such as water ; 

 thus the error arising from an elevation of temperature was, as 

 far as possible, avoided (12), the water itself being inadequate to 

 conduct any portion of the charge (9). The battery employed 

 in these experiments was suspended by balance-weights in a con- 

 venient frame, Fig. 4, so as to remove it at pleasure from the 

 acid, the latter being contained in a vessel of wood, having an 

 external glass-tube rt, and a graduated scale, by which the 

 quantity of metal immersed within could be correctly ascer- 

 tained. 



17. Previously to examining the indications on the electrome- 

 ter E, Fig. 3, with a given wire mn, the force of the battery 



