186 APPLIED SCIENCE 



points from which the influence is radiated to the charged material. 

 The tube itself is grounded, but the line wire is connected directly 

 with the cable inside of the tube. The connection is made through 

 a convenient form of removable socket at the end of each inductor. 

 The inductor is placed at some point in the machine where the 

 charged material may pass by it at a distance of from 1 to 3 in., 

 and the material becomes instantly neutralized thereby, even when 

 running at a speed of 1000 ft. per minute. On a printing press, the 

 inductor is placed across the press so as to treat the paper just 

 after it leaves the cylinder or at least before it goes into the pile. 



Electricity may be detected in some substances, such as cotton, 

 glass, and wool, better than in a metal like silver, because the first- 

 named substances are non-conductors and do not allow the electri- 

 city to escape easily while the reverse is true in the case of conductors. 

 Moist air is a far better conductor than dry air; hence, electricity 

 shows itself on cotton when the air is dried. In order to keep the 

 air moist, humidifiers (apparatus for discharging moisture in the 

 air) are distributed throughout cotton mills. 



221. Lightning. Much of the electricity of the air is 

 caused by the rubbing of moist air against dry air. A great 

 deal of moisture is made by the sun or wind turning into 

 vapor or mist the salt water of the ocean. More water is 

 turned into vapor during the heat of summer and autumn 

 than in winter and for this reason there is more lightning 

 in warm weather than in cold. The electricity in the air 

 in clear weather is generally positive, but during fogs, rains, 

 or snows it tends to change to negative. Sometimes it 

 happens that two clouds, one charged with positive electri- 

 city and the other with negative electricity, come near each 

 other. The two kinds of electricity then rush together and 

 we see a flash of lightning and hear thunder. Lightning is 

 the same thing as a spark from an electrical machine, the 

 only difference being that a flash of lightning is sometimes 

 several miles long arid the spark only a few inches, 



