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Our Surroundings 



Faraday discovered that a magnet moved within a coil of wire 

 will start a current of electricity flowing through the wire. This 

 discovery led to the great dynamos and generators which today 

 supply practically all of our electricity. His experiments with 

 glass and the electromagnet helped the art of making optical 

 lenses. He died in 1867. 



Henry. Joseph Henry was born in Albany, New York, in 

 1797. He received his education in the public schools and in 

 the Boys Academy of his native city, and at the age of twenty- 

 seven became professor of mathematics in the academy. 

 Here he experimented in electricity and electromagnetism, and 

 made discoveries of the greatest importance in the develop- 

 ment of these phases of science. 



Oersted's discovery, a few 

 years before, of the relation- 

 ship existing between elec- 

 tricity and magnetism had 

 aroused world-wide interest, 

 and all progressive physicists 

 were engaged in making in- 

 vestigations along these lines. 

 Henry was one of the men 

 most interested. He discov- 

 ered the principle of electro- 

 magnetic induction about the 

 same time that Faraday did, 

 although he did not publicly 

 announce it. This discovery 

 was one of the most important 

 in the history of science. 

 From it has developed most 

 of the modern applications of 

 electricity. He demonstrated that the number of turns in the 

 wire of an electromagnet as well as the amount of current pass- 

 ing through its coils had much to do with its magnetic strength. 

 He also showed that by binding the magnet with many turns 

 of fine wire it was possible to make up for the loss of current, 



JOSEPH HENRY 



Made many discoveries relating to 

 induced electric currents. 



