t)6Ó 



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two separate spaces, viz. tlie 

 measuring space c : a flat brass 

 cylinder, and the ionisation space 

 ƒ: a brass cylinder of volume 

 1 litre ; the two cylinders are 

 insulated from each other by 

 ebonite. 



In the measuring space is the 



metal needle b, supported in the 



middle by a second metal needle 



(/. insulated by amber ; b -\- d 



together form the conductor, which 



is charged by the ionisation current. 



In c is also found the very thin 



aluminium strip a, which a few 



mm. above b is fastened to a thin 



metal rod with mirror, suspended 



on a Wollaston wire, which is 



fastened to a torsion head insulated 



by means of ebonite. 



Through a perforation in the amber and in the ebonite a rod / 



can be brought in contact with the needle (/. 



In this way a, b -\- d, c, and ƒ, can therefore be separately brought 

 in a conductive connection with a storage battery or with earth ; 

 c rests on a bottom plate, to which legs are fastened which support 

 the apparatus. 



The charging of the apparatus before use. 



In what follows we shall examine from the course of the lines of 

 force, what state arises in the space c, and how this takes place, 

 when the system is charged : the lower cylinder ƒ is of no 

 account as regards this, as it does not belong to the measuring 

 system proper. 



The method of charging is founded on this that the two needles 

 a and b, which with untwisted position of a form an angle, let us 

 say of 30°, will still have this position with respect to each other, 

 when the system is in the charged state, in which latter case, however, 

 lines of force run between the different conductors. 



We begin to charge a to a constant potential, e. g. to, + 20 

 volts, keeping b and c still at potential volt. If for the sake of 

 simplicity we first imagine the state as it would be without the 

 presence of b. the course of the lines of force would be as follows: 

 lines of force would start from a, and end upon the bottom, the walls, 



