CHAP. I ] ELECTRICITY AND MAGNETISM. 



47 



to the conductor, it discharges the electricity so effect- 

 ually at its point that only the shortest sparks can be 



Fig. 26. 



drawn at the knob, while a fine jet or brush of pale 

 blue light will appear at the point. If a lighted taper 

 be held in front of the point, 

 the flame will be visibly blown 

 aside (Fig. 26) by the streams 

 of electrified air repelled from 

 the point. These air-currents 

 can be felt with the hand. 

 They are due to a mutual re- 

 pulsion between the electrified 

 air-particles near the point and 

 the electricity collected on the 

 point itself. That this mutual 

 reaction exists is proved by 

 the electric fly or electric 

 reaction -mill of Hamilton 

 (Fig. 27), which consists of 

 a light cross of brass or straw, suspended on a pivot, 



