18 COMBINED OUEKENTS. CHAP. H. 



duced,' passing in contrary directions and being 

 equal to each other, counteracted each other's effects, 

 and consequently there was no action upon the 

 needle. 



Let the cells be filled thus, acid | alkali | acid | 

 alkali, and place the electrodes in the extreme cells ; 

 we have here three acting points in the circuit: 

 at one point the current is in one direction, 

 and in two others in a contrary direction ; and the 

 action upon the needle in this instance will shew 

 the differential result. 



The same observations may be made in regard to 

 a voltaic battery, by altering the arrangements of 

 the metals, so as to have a combined action in one 

 case and an interfering action in the other. 



I have entered somewhat fuUy into the develope- 

 ment of electric action during chemical action, in 

 consequence of its immediate bearing upon the 

 question of the developement of electric force during 

 organic action; and I ought now perhaps to allude 

 to thermo-electric action, and to the facts connected 

 with the so-caUed catalytic action or the combining 

 power of platinum ; but to enter fully into these 

 questions would occupy too much space, and I must 

 therefore refer my readers to the pubhshed treatises 

 on Electricity for further information upon these 

 subjects. 



Let us now call to mind the peculiar characters, 

 without alluding to the origin of the power, whether 

 from heat, chemical action, friction, &c. which are asso- 



