SOURCES OF ELECTRICITY 87 



5. 1803 : 312. The Principle of the Dynamo. 



a. 1801 : 312-314. Electrification by Friction. 



b. 1801 : 337-340. The Simple Voltaic Cell. 



c. ] 801 : 378-381. Electromagnetic Induction. 



d. 1804:434-435. Electrification. 



e. 1804:465-468. Voltaic Cell. 



/. 1805 : 380-391. The Simple Voltaic Cell. 



g. 1805 : 430-437. The Electric Dynamo. 



h. 1806 : 481-484. Electrification by Friction. 



i. 1806 : 501-502. Electricity Developed by Chemical Action. 



j. 1807:353-356. Voltaic Cell. 



k. 1807 : 389-404. Electromagnetic Induction. 



I. 1808 : 293-294. The Electric Current. 



Experiment 28. Sources of Electricity. 



Apparatus : Pith ball on stand, rubber rod, dry cell, strips 

 of zinc and copper, or carbon, glass tumbler, magnetic needle, 

 six-inch magnet, fifty feet insulated copper wire No. 20. 



Materials : Dilute sulphuric acid (one part acid to nine parts 

 water) . 



a. Bring the rubber rod near the pith ball. Nothing hap- 

 pens. Dry the rod, rub it, and bring it near the pith ball. 

 What happens ? Let the pith ball touch the rubber rod arid 

 again approach the rubber rod. Tell what happens, and give 

 the laws of electric charges. Note : When the pith ball 

 touched the rod, it became charged with the same kind of 

 electricity. Before being touched, it had induced in it the 

 opposite kind of electricity. 



6. Wind ten feet of insulated wire around the compass in a 

 thin coil, piling some of the windings upon others. This 

 makes a galvanometer, and to use it the coils should run north 

 and south. Attach the dry cell and note how the needle turns. 

 Reverse the connections and see in which direction the needle 

 turns. Take as your guide that the electricity comes from the 



