Passage of Electricity through Gases. 185 



degree, the conditions are fundamentally altered, and a direct 

 comparison of the resistance may give results different from 

 those obtained by the above-mentioned experiments. 



2. Influence of the surrounding spaces. — If the spaces sur- 

 rounding the negative electrodes are not alike, different ten- 

 sions are necessary in order to produce discharge. With 

 cylindrical electrodes of different thickness, but the same 

 length, enclosed in tubes of equal diameter, the thicker elec- 

 trodes require a greater charge, because the repelling reaction 

 of the homonymous charge of the glass envelope on the elec- 

 tricity of the surface of the electrode is greater ; and also the 

 electrode itself, in consequence of its larger surface, requires a 

 greater quantity of electricity to charge it with equal tension 

 at all points. If, when simply connected with a Holtz's ma- 

 chine, we suppose the potentials to be the same at every point 

 of the electrode, the electrode whose thickness is represented 

 by n would receive and discharge at every discharge more than 

 n times the quantity of electricity received and discharged by 

 that whose thickness is represented by unity. If, however, two 

 tubes containing dissimilar negative electrodes are inserted side 

 by side in the circuit of a coil, the relations are much more 

 complicated and not so easily perceived as in the above-men- 

 tioned case. The current would divide itself in proportion to 

 the extent of the surfaces ; in consequence of the greater den- 

 sity of the electricity on the thicker electrode necessary for the 

 discharge, the discharge at the n times thicker electrode would 

 begin later and cease earlier, and therefore less than n times 

 the quantity of electricity would be discharged through it — 

 provided always that all the electricity did not flow out through 

 the thinner electrode, and also that the electricity is conveyed 

 to the electrodes from the coil with such velocity that a back- 

 ward current to the thinner electrode of the electricity flowing 

 to the thicker electrode does not take place during the dis- 

 charge. On the contrary, the gas may be more forcibly driven 

 from the shorter electrode in consequence of the greatercharge, 

 whereby a greater body of electricity will follow the initial 

 discharge if there be sufficient gas to convey it. 



3. Influence of pressure. — If two similar tubes, but contain- 

 ing gas at different pressures, be inserted side by side in the 

 circuit, there is considerable complication in the results. 



According to our experiments the tube I. with the denser 

 gas would require a greater charge for the production of the 

 discharge, and consequently the discharge in it would begin 

 later and cease earlier ; therefore a less body of electricity 

 would pass through tube I. than through tube II. with the rare- 

 fied gas, supposing that the electricity from the coil flowed 



