1889.] Electrolytes to very rapidly alternating Currents. 289 



the resistance of the graphite film was 6*7 ohms, and that of the 

 sulphuric acid 7'2 ohms ; thus we may say that the ratio of the specific 

 resistances of graphite and sulphuric acid is the same when the 

 currents are steady as when they are reversed 10 8 times per second. 

 Since the ratio of the resistances of such dissimilar things as graphite 

 and electrolytes remains the same, we may conclude that the resistances 

 themselves remain unaltered. The method described above for com- 

 paring the resistances of electrolytes is one that can be very easily 

 and quickly applied, and only requires the simplest apparatus : an 

 induction coil, or, if that is not available, an electrical machine, being 

 all that is required. The method has the advantage of avoiding the 

 use of electrodes, as all the circuits in the electrolyte are closed. 



Since electrolytes are transparent, they must, if the electromagnetic 

 theory of light is true, act as insulators when the currents are reversed 

 as often as light vibrations, or about 10 15 times per second. We have 

 seen, however, that they conduct as well when the currents are 

 reversed 10 8 times a second as when they are steady; thus the mole- 

 cular processes which cause electrolytic conduction must occupy a 

 time between IQr 8 and 10~ 15 seconds. 



Another point which can be settled by this method is, whether a 

 vacuum is a conductor or an insulator. According to one view the 

 great resistance which a highly exhausted vessel offers to the passage 

 of electricity is due to the difficulty of getting the current from the 

 electrode into the rarefied gas : when once the current has got there, 

 there is, according to this theory, no further resistance to its passage : 

 if this theory is correct, a highly exhausted receiver placed between 

 the primary and secondary circuits ought to stop the sparks in the 

 latter, as since all the circuits are closed there ought to be no obstacle 

 to the passage of the induced currents. In order to test this I took 

 a box, 50 c. by 50 c. by 4 c., the top and bottom of which were sheets 

 of plate-glass fitting into wooden sides ; the sheets of glass were also 

 supported by five ebonite pillars placed at equal intervals over their 

 surface. The box was repeatedly dipped into a bath filled with 

 melted paraffin until it was surrounded by a coating of paraffin about 

 2 c. thick. The paraffin was then smoothed over with a hot soldering 

 iron, and then covered with a layer of shellac varnish. The box was 

 then exhausted by a mercury-pump, and it was found that the pres- 

 sure could be reduced to about 1 mm. of mercury, but no further. 

 When this vacuum was placed between the primary and secondary 

 coils it did not produce the slightest effect upon the sparks, so that 

 its conductivity must be very small indeed compared with that of the 

 electrolytes used in the preceding experiments. I am having an 

 earthenware vessel made with which I hope to repeat the experiment 

 at much higher exhaustions. 



I also tried whether the conductivity of the electrolyte was altered 



