46 



THE DIFFUSION OF GASES THROUGH 



the last case of the second series for the case of the metal tube was the limit 

 of stable equilibrium approached. When the potential is unsteady it is 

 necessary to keep the disk some distance below this. For the case of the 

 large values of V the guard ring should have been larger, but the results 

 as a whole betray no discrepancy attributable to this effect. To detect it, 

 facilities for constant potentials of the degree stated would have to be 

 available. In conclusion, the simplicity of the apparatus as a whole 

 deserves remark. 



Table 1 1 . 



-Measurements of potential, V' = 2.26X\o^pg ir^/R-)lD'; p= i;2r = o.854cm. 

 22? = 6.65 cm. Al tube 30 cm. long; weight, 13 grams. 



Part II. Absolute Electrometry by Aid of the Cartesian Diver. 



32. Introductory. — In the above methods the stem between the floats 

 and the movable disk of the condenser passed through the surface of the 

 liquid. This introduces capillary forces which are annoying and liable to 

 be of serious magnitude. To obtain the utmost sensitiveness available, 

 the stem must be discarded and the movable disk in question moimted on a 

 Cartesian diver — the whole apparatus, i. e., both plates of the condenser 

 and accessories, being submerged in a non-conducting clear paraffin oil. 

 The remarkable delicacy in v/eighing, instanced in the above experiments on 

 the diffusion of gases, contributes to the success of the present experiments. 



