ELECTRIFICATION OP AIR, VAPOUR OF WATER, AND OTHER GASES. 197 



The air h;id to pass through these and the long length of tubing before reaching the 

 testing filter at the electrometer. The testing filter consisted of a block-tin tube 

 with two wire gauzes and one plug of cotton wool. Twenty experiments were made 

 on air drawn from the aperture of the funnel near its lower end, and with jet from 

 full pressure of water. The following are mean results, for 120 strokes of the 

 pump : 



These results show that a large proportion of the electricity was taken, by the 

 7 gauzes and 6 plugs, from the air before it reached the testing filter. 



31. Extracting the air with no water falling gave no perceptible electrification. 



32. With the water again at full pressure, and falling on the sloping plate fixed 

 into the bottom of the funnel, the negatively electrified air was drawn from the 

 bottom aperture through different- filters at different speeds. Two experiments at 

 each speed were usually made, and whenever possible the deflection for 120 strokes 

 of the pump was noted. In some cases, however, the reading exceeded 8 volts, and 

 went off the scale with much fewer strokes ; but to preserve uniformity the tabular 

 results given below are a,ll calculated for 120 strokes. 



Results 2 and 4 are in accordance with Results 2 and 3 of 8 68. 



33. A metallic water-dropper was now fixed into the lid of the funnel, and the 

 metallic plate at the bottom removed. A strong solution of common salt was placed 

 in the dropper, and allowed to fall down the centre of the funnel into a basin below. 



