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THE POPULAR SCIENCE MONTHLY 



If no point exist on the conductor, a single turn of the handle of 

 the machine suffices to cause the straw to stand out nearly at right 

 angles to the stem. If, on the contrary, a point be attached to the 

 conductor, you cannot produce a large divergence. The reason is, 

 that the electricity, as fast as it is generated, is dispersed by the 

 point. The same effect is observed when you present a point to the 



Fig. 20. 



conductor. The conductor acts by induction upon the point, causing 

 the negative electricity to stream from it against the conductor, 

 which is thus neutralized almost as fast as it is charged. Flames and 

 glowing embers act like points ; they also rapidly discharge electricity. 



The electricity escaping from a point or flame into the air renders 

 the air self-repulsive. The consequence is that, when the hand is 

 placed over a point mounted on the prime conductor of a machine in 

 good action, a cold blast is distinctly felt. Dr. Watson noticed this 

 blast from a flame placed on an electrified conductor, while Wilson 

 noticed the blast from a point. Jallabert and the Abbe Nollet also 

 observed and described the influence of points and flames. The blast 

 is called the "electric wind." Wilson moved bodies by its action; 

 Faraday caused it to depress the surface of a liquid ; Hamilton em- 

 ployed the reaction of the electric wind to make pointed wires rotate. 

 The " wind " was also found to promote evaporation. 



Hamilton's apparatus is called the " electric mill." Make one for 

 yourself thus : Place two straws S S, S' $', Fig. 21, about eight inches 

 long, across each other at a right angle. Stick them together at their 

 centres by a bit of sealing-wax. Pass a fine wire through each straw 

 and bend it where it issues from the straw, so as to form a little 

 pointed arm perpendicular to the straw, and from half an inch to 

 three-quarters of an inch long. It is easy, by means of a bit of cork 

 or sealing-wax, to fix the wire so that the little bent arms shall point 

 not upward or downward, but sideways, when the cross is horizontal. 

 The points of sewing-needles may also be employed for the bent arms. 

 A little bit of straw is stuck into the cross at the centre, to form a 

 cap. This slips over a sewing-needle, N, supported by a stick of 



