180 Prof. G. Wiedemann on the Laws of the 



are used, the electrical tension is greatest at their front free 

 ends ; in this case also the repulsion of the electricity accu- 

 mulated round the electrodes on the glass, which spreads with 

 decreasing density, at the ends of the electrodes is relatively 

 least. The discharge, therefore, soon passes under rather 

 high pressure out of these front ends. If the air is more 

 rarefied, the tension necessary for the commencement of the 

 discharge, as well as the charge of the surrounding glass, and 

 also the difference of the tension necessary for the discharge 

 at different parts of the electrodes, are smaller, particularly at 

 the negative electrode, which always requires a smaller charge. 

 The electricity conveyed from ihe electric machine, or from 

 the inductorium, is sufficient then to produce the discharge 

 onto the negative electrode, and even at a certain dis- 

 tance from its end. On the positive electrode the discharge 

 begins only when the charge is stronger, therefore the dif- 

 ferences of charge at the various parts of the electrode are 

 greater, and the discharge passes almost exclusively from the 

 front end of the positive electrode. 



If the part of the tube surrounding the negative electrode 

 be narrower, a more powerful charge is necessary for the dis- 

 charge on the sides of the electrode than if it be wider, on 

 account of the repulsion of the electricity upon the tube. 

 The discharge contracts, therefore, more and more at the end 

 of the electrode, and, in consequence of the repulsion through 

 the negatively charged glass, it can spread a long way towards 

 the positive electrode. * 



If, further, two tubes, with a small and a large negative 

 electrode respectively, are inserted consecutively in the cir- 

 cuit, a discharge begins as soon as the tension has reached 

 a certain degree on the negative electrode. To attain this a 

 more powerful charge is required at the larger than at the 

 smaller electrode. If, then, the discharge begins at the 

 former, the body of electricity flowing to the latter will be 

 relatively greater than is necessary, the air repelled by the 

 initial discharge will be still more accelerated, and the halo 

 will spread further than from the larger negative electrode. 



If two wire electrodes, covered on their lateral surfaces 

 by a glass coating, be fixed axially in a cylindrical tube, one 

 (I.) at the end, the other (II.), bent, from the side towards the 

 centre of the tube, so that it turns its free surface away from 

 the first electrode, and if the electrodes be so far removed 

 from one another that their influence on one another is only 

 slight, the glass around the electrode II., when the latter is 

 negative (particularly if the pressure be low), will be only 

 slightly and almost uniformly charged (according to the feeble 



