6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 76 



the large battery of 2000 cells he had had constructed. Using two 

 sticks of charcoal connected by wires to the terminals of this very 

 powerful battery, he demonstrated before the Royal Society the light 

 produced by touching the sticks together and then holding them apart 

 horizontally about three inches. The brilliant flame obtained he called 

 an " arc " because of its arch shape, the heated gases, rising, assuming 

 this form. Davy was given the degree of LL. D. for his dis- 

 tinguished research work, and was knighted on the eve of his mar- 

 riage, April II, 18 12. 



RESEARCHES OF OERSTED, AMPERE, SCHWEIGGER AND STURGEON 



Hans Christian Oersted was a professor of physics at the Uni- 

 versity of Copenhagen in Denmark. One day in 1819, while ad- 

 dressing his students, he happened to hold a wire, through which 

 current was flowing, over a large compass. To his surprise he saw 

 the compass was deflected from its true position. He promptly made 

 a number of experiments and discovered that by reversing the current 

 the compass was deflected in the opposite direction. Oersted an- 

 nounced his discovery in 1820. 



Andre Marie Ampere was a professor of mathematics in the Ecole 

 Polytechnic in Paris. Hearing of Oersted's discovery, he immedi- 

 ately made some experiments and made the further discovery in 1820 

 that if the wire is coiled and current passed through it, the coil had 

 all the properties of a magnet. 



These two discoveries led to the invention of Schweigger in 1820, 

 of the galvanometer (or " multiplier" as it was then called), a very 

 sensitive instrument for measuring electric currents. It consisted of 

 a delicate compass needle suspended in a coil of many turns of wire. 

 Current in the coil deflected the needle, the direction and amount of 

 deflection indicating the direction and strength of the current. 

 Ampere further made the discovery that currents in opposite direc- 

 tions repel and in the same directions attract each other. He also gave 

 a rule for determining the direction of the current by the deflection of 

 the compass needle. He developed the theory that magnetism is 

 caused by electricity flowing around the circumference of the body 

 magnetised. The Ampere, the unit of flow of electric current, was 

 named in honor of his discoveries. 



In 1825 it was shown by Sturgeon that if a bar of iron were placed 

 in the coil, its magnetic strength would be very greatly increased, 

 which he called an electro-magnet. 



