22 



distant from each other, and of 8, 16, 24, 32, and 40 wires 

 to the inch respectively. 



The crossed gauzes give results falling very well into line 

 with those from the paralled wire grid, in which the smaller 

 the mesh the harder it was to obtain saturation. It is not- 

 able that with all the intermediate gauzes an approach is 

 shown to the same value of maximum current as the field 

 strength is increased. With very fine gauzes very intense fields 

 would seem necessary to drag all the ions through the gauze, 

 while with gauzes much broader than about 16 to the inch 

 ions are apparently readily drawn from distances considerably 

 below the gauze. 



All the curves given were obtained from results of ex- 

 periments in which the bottom gauze was positive. When 

 it is made negative, and the top gauze also negative, very 

 little difference is found in curves for strong fields : with 

 weak fields'the values obtained with the gauze positive are 

 a^-=a,-rule slightly higher than with the gauze negative. 



Of numerous gauzes tested, the 20 to the inch crossed 

 brass gauze, with diameter of strand *01 in., gave the nearest 

 approach to an early saturation, and was used in subsequent 

 experiment'g: 



Rutherford, in his paper already referred to, has shown 

 tkat -gauzes exert a large influence in discharging ions from 

 gas blown through them ; he finds that the effect depends, ap- 

 parently, upon the ratio of the space occupied by the air 

 between the meshes, and the extent of metal in the gauze. 

 As, liowever, his experiments were performed with a field 

 acting upon one side of the gauze, it seemed necessary to 

 repeat the experiments with no field acting on the gauze, as 

 from the experiments described above it would seem that 

 under this condition the discharging power of the gauze 

 should be even greater than as determined by Rutherford. 



The experiment was arranged so that gauzes could be 

 set parallel to and "5 cm. below the bottom gauze of the 

 chamber used in the previous experiments. A field of 300 

 volts per cm. was applied to the lower side of the electro- 

 meter gauze and 100 volts per cm. above it, thus preventing 

 ions from escaping through the electrometer gauze. Read- 

 ings of the current were taken with and without the gauze 

 which was to be tested, in position. The ratio of these two 

 readings was taken as a measure of the discharging power 

 of the gauze. 



In fig. 7 are plotted the results for jDarallel grids cor- 

 responding to Table B. Theie appears a certain value of 



