ANIMAL AND VEGETABLE 91 



CHAPTER VI 

 INDUCTIVE CAPACITY 



As a good deal depends upon a proper appreciation of 

 the function of a condenser, as that apparatus is used in 

 telegraphy, it may be well to make it clear ; taking as my 

 authorities Sir Wm. Preece, F.R.S., and Sir James Sive- 

 wright, joint authors of Telegraphy. 



" When a quantity of electricity flows through a line 

 in the form of current, the first portion of the current is 

 retained or accumulated upon the surface of the wire, in 

 the same way that a charge is retained or accumulated upon 

 the surface of a Ley den jar. The quantity accumulated 

 depends (1) upon the length and diameter of the wire, 

 (2) upon its distance from the earth and earth-connected 

 bodies, (3) upon the insulating medium surrounding the 

 conductor. 



" The effects of capacity are, first, that it absorbs all 

 the electricity of a short momentary current and prevents 

 the appearance of any current at the distant station, and, 

 second, that as it absorbs the first portion of every current 

 sent, it has the same effect as if it retarded or delayed the 

 first appearance of the current at the distant end. Thus 

 the apparent velocity of the current is diminished more or 

 less in proportion to the capacity of the circuit, velocity 

 being in the inverse ratio to the capacity. 



" ' Condenser ' is a term applied to an apparatus 

 usually composed of alternate layers of tinfoil and paraffined 



