Electricity 



251 



Take a wire long enough to go from one instrument to 

 the other. Fasten the bare ends of this wire into the right- 

 hand binding post of the instrument at your left, and into 

 the left-hand binding post of the instrument at your right ; 

 that is, connect the binding posts that are nearest together, 

 as in Figure 141. 



Now connect one wire from the laboratory battery to the 

 free post of the right-hand instrument. Connect the other wire 

 from the laboratory battery to the ground through a faucet, 

 radiator, or gas pipe, making the connection firm and 

 being sure that there is a good, clear contact between the 

 bare end of the wire and the metal to which the wire is 

 attached. 



Make another ground connection near the left-hand 

 instrument ; that is, take a wire long enough to reach from 

 some pipe or radiator to the left-hand telegraph instrument, 

 bind one bare end of this wire firmly to a clean part of the 

 pipe and bring the other end toward the instrument. Be- 

 fore attaching this other end to the free binding post of the 

 left-hand instrument, be sure to open the switch beside the 

 telegraph key by pushing it to your right. Close the switch 

 on the other instrument. Now attach the free ground wire 



To Ground 



Fii. 141. Diagram showing how to connect up two telegraph instruments. 

 The circles on the tables represent the binding posts of the instruments. 



