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SCIENCE AND PRACTICE. 259 



exact inquiry in electrical science is built up. We will see 

 now, as an instance, what it affords us when we combine 

 elements together in different ways. 



When the poles of a pair of plates are joined together, the 



intensity, I, of the current passing in every section of the 

 p 



circuit is, I = . There are two principal ways in which 



r + p 



a number of galvanic pairs may be connected together. 

 1st. They may be connected in series for intensity, so as to 

 add their electro-motive forces and resistances together ; and, 

 2ndly, they may be connected parallel to each other for 

 quantity, as it is called, so that the electro-motive force of 

 the combination remains the same, but the surface of the 

 plates is increased, and hence the resistance, in the same 

 measure, diminished. 



First, let n elements be connected so that the negative pole 

 of the first element is joined to the positive pole of the second, 

 the negative pole of the second to the positive pole of the 

 third, and so on, up to the ntln. element. We have then what 

 is vulgarly called an " intensity battery," and the intensity 

 of the current of each individual element of the series, if they 

 are of the same kind and size, will be 



I = 5 = E . . (III. 



p +r + (n-~ l)r p + nr ' 



and that of the whole battery, 



I n = n ^_ (IV. 



p + nr 



When the resistance n r of the battery is so small in com- 

 parison with > that we can, without appreciable error, neglect 

 it, the intensity of the whole battery becomes 



I H = .... .(V. 



P 



that is to say, that when the resistance of the battery is very 

 small in comparison with the resistance of the circuit 

 exterior to the battery, the strength of the current is 

 increased in direct proportion to the number of elements 

 added to it. 



s 2 



