ELECTRICAL CONNECTIONS 173 



Series is carbon to zinc throughout ; Parallel is carbon to 

 carbon and zinc to zinc ; and Series-parallel partly carbon 

 to zinc and partly carbon to carbon and zinc to zinc. The 

 first increases the electromotive force without increasing 

 the current quantity, the second increases the current 

 without augmenting the electromotive force, while the 

 third permits of an adjustment of both current and electro- 

 motive force to meet requirements. 



Nature employs direct — not alternating — current and 

 therefore the sectional area of the conductor must vary in 

 proportion to the quantity of current to be suppKed. I say 

 " must " because resistance is in the inverse ratio to sectional 

 area and the natural electromotive force is constant. If 

 you require more water in a given time and the pressure 

 cannot be altered you must have a larger pipe. 



In the vegetable world all three methods are resorted to 

 but the one most in vogue is the series-parallel. 



As will be seen also in the Chapter upon Acorns the seeds 

 of the Oak are always joined up in series. There are only 

 a few of them upon each stalk so that the latter does not 

 need to be very thick. The stalk is, of course, a continua- 

 tion of the feed wire from the earth. 



fig. fiS 



The apex of the seed is left slightly open, in order that 

 the circuit may be completed. 



In practical electric lighting, as carried out in our houses, 

 two wires are employed but for the reason above given 

 Nature can dispense with one of them. 



In the incandescent lampholder there are two contacts, 

 to allow the current to enter at one end of the filament 

 and pass out at the other. In the Acorn — while it is still 

 attached to the tree — the apex is open, and two contacts 

 at the base of the seed are not called for. But the two 

 things are very much alike. 



