88 INTRODUCTION TO GENERAL SCIENCE 



carbon of the dry cell and returns to the cell through the zinc. 

 The carbon is called positive, +, and the zinc negative, . 



c. Take a strip of copper and one of zinc. Attach them by 

 wires to your galvanometer and place them in a glass tumbler. 

 Pour in a little of the dilute solution, watching the needle of 

 the compass. What happens? In what direction does the 

 needle turn? Which is +, copper or zinc? The current soon 

 decreases on account of chemical changes taking place within 

 the solution and because the bubbles of hydrogen, which are 

 set free, offer resistance to the flow of the current. Shake the 

 copper strip, and watch the needle. 



d. Wind forty feet of wire around the magnet, in a close 

 coil, after first winding the magnet with twenty turns of 

 paper. Remove the coil and pull out the paper. Attach the 

 coil to the galvanometer by means of wires which are at least 

 six feet long. Now, watching the needle, push one end of the 

 magnet into the coil. Note deflection of needle. Which 

 way did the current go? Where did the electricity come 

 from? Again watching needle, remove the magnet. Con- 

 clusions? Repeat with the other end of the magnet. Con- 

 clusions ? 



65. APPLICATIONS OF ELECTRICITY 



In this section we shall take up only those applications of 

 electricity which include magnetism. In Sections 66 and 67 

 other applications will be studied. 



Since the magnetism by electricity lasts only while the 

 source of current is connected with the magnetizing coils, we 

 can regulate or stop and start the magnetism at will. The 

 electric bell is the simplest example. The electromagnet 

 pulls the hammer against the bell, but when the hammer is 

 nearly there, the current is broken by means of the spring 



