MR. DANIELL ON VOLTAIC COMBINATIONS. 49 



luted acid and solution of copper in the membrane, with a copper ball one inch dia- 

 meter, deflected the galvanic needle 45°. 



With the calorific galvanometer it moved the index to 25°. 



Being desirous of ascertaining whether the same difference between the reversed 

 combinations would exist in a series as in single circuits, I compared together three 

 copper cylinders with three zinc rods, and three zinc cylinders with copper rods, by 

 means of a voltameter. The former produced in ^ hour 3*6 cubic inches of gas. 

 The latter produced in J hour 1'7^ cubic inches: indicating, as before, that when the 

 generating surface constituted the circumference of the arrangement, the force was 

 only the half of that which was evolved when it formed the centre. 



In the copper cylinder it made no difference whether the zinc ball or rod were 

 placed in the centre, or nearly in contact with the side. 



I next took an oval copper plate, the diameters of which were 13§ inches by 10 

 inches, and soldered a copper wire at one extremity of the longest diameter, in a 

 perpendicular position, and placing it in an earthen pan, covered it with a depth of 

 4J inches of the acid solution of copper. Over its centre I suspended, by means of a 

 cross bar, a bag of membrane filled with the dilute acid ; and nearly at the bottom 

 of this I placed an amalgamated zinc ball, connected with a varnished copper wire. 

 I then formed a circuit by means of the magnetic galvanometer, and the needle was 

 deflected 55°. It remained perfectly steady for half an hour, when the plate was 

 taken out and examined. It was found covered with fresh precipitated copper, the 

 coat being a little thicker at the centre, and becoming thinner by almost insensible 

 gradations towards the edge. At one point it had begun to turn round the edge and 

 to diflfuse itself on the under side. 



The zinc ball was next placed just below the surface of the liquid in the pan, so 

 that its least distance from the conducting plate was the same as when placed in the 

 centre of the sphere. Upon completing the circuit the needle was deflected 45°. 



The zinc ball was now drawn up in the tube so as to remain immersed in the acid, 

 but two inches above the level of the solution ; the needle was still deflected 35°. 

 Upon again replacing it below the level it returned to 45°, and fell to the same amount 

 upon once more drawing it up. In this case the lateral diffusion of the efficient force 

 must have been prevented for the first two inches of its course ; the mode of its after 

 propagation was the subject of my next inquiry. While the apparatus was in this 

 position, one zinc rod, and afterwards two, connected together, were immersed into 

 the acid, so as to extend through the whole depth of the solution, without deflecting 

 the needle more than 55°. 



In these experiments the stem of the copper wire which was soldered to the copper 

 plate was covered with precipitated copper as well as the plate. In subsequent ex- 

 periments it was protected by varnish. 



In order effectually to cut oflf the lateral radiation from the zinc ball, I placed it 

 in a glass tube, six inches long; and over the lower aperture, which was 1§ inch 



MDCCCXXXVIII. H 



