25 203 



when u = {v^ — v^) — i^'e^f^i) is the change in the potential difference between the 

 electroscope vessel and the ionisation chamber that has been produced. 



The most convenient way of charging the inner system of conductors is by 

 means of influence. A rod provided with an insulated handle, is brought into 

 contact with the rod g, and a charged body, a rod of sealing wax for instance, 

 is brought close to the upper end of the charging rod until the leaf has made a 

 suitable deflection. Then the charging rod is taken off and the cover of the 

 electroscope vessel put on. In order to impart a sufficient charge to the inner 

 cylinder it is necessary that the end of the charging rod toward which tiie rod of 

 sealing wax is brought, be flat shaped. 



In order to produce the potential difference between the electroscope vessel 

 and the ionisation chamber I used 10 small dry cells (Hellesen's pattern). These 

 were embedded in paraffin in two wooden boxes containing four and six cells 

 respectively. In each box the cells were connected in a series, and one pole of every 

 alternate cell was attached to one of the copper stoppers which formed the bottom 

 of the small holes in the thick ebonite plate in the lid of the box, (see Fig. 5). The 

 copper stoppers render the holes mercury-tight, and when the battery is to be used 

 the holes are filled with mercury. When the poles of the cells are to be connected 

 to the electroscope vessel and the ionisation chamber, the ends of the connecting 

 wires are placed in the mercury. In transit the holes in the ebonite plate are 

 emptied of their contents of mercury, and then the poles of the cells are represented 

 by the copper stoppers in the bottom of the holes. In this way the cells are 

 protected against injury by accidental overstraining. Hence the cells remained 

 constant during the whole journey. 



Of course the connections between the testing apparatus and the battery are 

 arranged at the beginning of every experiment, that is to say, before the adjust- 

 ment of the microscope, so that one is able to make the greatest change in the 

 potential difference that the cells in use permit, without altering the adjustment of 

 the microscope. If the inner cylinder is charged positively, then the positive 

 terminal of the battery should be connected with the electroscope vessel. 



As the change produced in the potential diflerence between two consecutive 

 observations depends on the rate of leakage, one must endeavour as far as pos- 

 sible to arrange that the intervals of time to be measured be kept within certain 

 limits, preferably about one minute. If the intervals are much longer, the measure- 

 ment takes too long, whilst on the other hand, if the interval be much shorter, 

 the inevitable errors will proportionally be so great as to affect seriously the 

 accuracy of the final results. 



When the ionisation is small and the downward movement of the leaf is 

 correspondingly slow, one does not need to move one end of the connecting wire 

 farther forward than one hole in the battery case at a time; the established altera- 

 tion in the potential difference (ve~Vb) then amounts to about 2.9 volts, i. e. double 



1). K. 1). Vidensk. Selsk. .Ski-., 7. lUekkc, natuividensU. ojj malheni. Afd. VIM. -1. 27 



