of Recombination of the Ioiis of Gases. 437 



pole being connected to earth. The plate B was connected 

 through a contact-lever, LM, mounted on an insulating 

 block, to one pair of quadrants of the electrometer, the other 

 being connected to earth. The pendulum interrupter was so 

 arranged as to make the current in the primary of the induction- 

 coil, to break the electrometer-circuit by knocking away the 

 lever LM, and then to break the battery-circuit shortly after- 

 wards. For this two other shunt-levers were required which 

 are not shown in the figure. A condenser, N, was introduced 

 into the electrometer-circuit to increase its capacity. A 

 steady difference of potential of 220 volts was applied between 

 the two plates. 



When the bulb was excited the ions on one side have to 

 travel over a distance of 8 cm. before they reach the plate B. 

 The object of the experiment was to determine the interval 

 between the starting of the rays and the arrival of the ions 

 at the plate B. It was found that there was only a small 

 deflexion of the electrometer until after a definite interval 

 had elapsed, when the deflexion increased rapidly. This was 

 taken as the instant when the ions had reached the electrode. 

 The deflexion of the electrometer was proportional to the 

 quantity of electricity that had passed from A to B during 

 the time between making the current and breaking the elec- 

 trometer-circuit. The electrometer itself was not connected 

 with its circuit until after the contacts had been broken. 



It was found that after the rays had been acting for '36 of 

 a second the electrometer deflexion commenced to increase 

 rapidly. A potential-difference of 220 volts was acting 

 between the plates, so that the electromotive intensity was 

 13'75 volts per cm. In the time "36 of a second, therefore, 

 under a potential gradient of 13*75, the ions have travelled 

 over a distance of 8 cm. This gives a velocity of the ion 

 of 1'6 cm. a second, and corresponds to the velocity of a 

 positive or a negative ion, for the time taken was found to 

 be independent of the sign of the ion. The sum of the 

 velocities of the positive and negative ions is therefore 32 cm. 

 per second — a result agreeing with that determined for air 

 by a completely independent method. The close agreement 

 between these two results affords strong evidence of the truth 

 of the theory by the aid of which the velocities of the ions 

 of different gases have been obtained. 



The velocities with which the ions move through the gas 

 are immensely greater than the velocity of the ions in the 

 electrolysis of liquids. The velocity of the hydrogen ion in 

 nearly pure water is 1'08 cm. per hour under a potential 

 gradient of 1 volt per cm.; so that the velocity of the hydrogen 



