178 Almy — Discharge-current from a 



Length of wire, 15 cm ; diameter, 0'0047 cm ; diameter of 

 cylinder, 94 cm ; pressure of the gas (air), ^4c'1 cm of Hg. The 

 variation of the constants, a, and b, when the sign of the dis- 

 charge is reversed, is, in the case of air, not large ; but in case 

 hydrogen is used a very large difference exists. 



The equation given above seems applicable to the discharge 

 under all the various conditions of the gas. Even after the 

 gas had suffered any amount of " deterioration," so that the 

 discharge that passed was decidedly less, the relation between 

 potential and current still exists, — with different values for the 

 constants, a and b. 



5. The applicability of this relation at widely different gas 

 pressures (varying from 20 cm to 80 cm of Hg.) was also estab- 

 lished. The variation of the discharge current, with gas pres- 

 sure, for a given apparatus, does not seem capable of any 

 simple formulation. It seems probable that this was due to a 

 difference in the rate and extent of the deterioration of the gas 

 at the different pressures, so that the constants obtained repre- 

 sent different conditions of the gas, beside differences of pres- 

 sure. The constants obtained are : 



Pressure. 



a. 



&. 



20' cm of Hg. 

 40" " " 

 15' " « 



3'55 



1-05 



•55— -65 



3-20 

 8-53 

 11-7— 12-2 



The dimensions of the apparatus were those given in the pre- 

 ceding section. 



6. For determination of the law of the variation of current 

 with the radius of the cylinder, three cylinders of suitably dif- 

 ferent radii, with discharge wires of the same size and length, 

 were mounted as the one used heretofore. Hydrogen, gen- 

 erated from hydrochloric acid with zinc, purified and dried by 

 the usual process, was passed into the cylinders in place of air, 

 as this gas shows less rapid deterioration with continued use. 

 Still, under the most favorable conditions that could be 

 obtained, the current given by a certain potential was subject 

 to considerable variation. 



It was found that to a certain degree of approximation, the 

 total discharge current is inversely proportional to the cube of 

 the radius of the cylinder, other dimensions being the same. 

 It is to be noticed that this relation holds most accurately 

 when the current in the cylinders compared is of the same 

 order of magnitude. It seems probable that the deviation 

 which occurs when the current in one tube is large compared 

 to that in the other may be due to more rapid deterioration of 

 the gas with increased discharge ; in fact, the deviation is 

 always most pronounced when the discharge is largest in both 

 tubes. 



