PROJECTS 641 



An incandescent lamp marked 40 watts indicates that it uses 

 40 watts of current per hour. A 40-watt incandescent lamp would 

 therefore burn 25 hours ( 1000 -r- 40) before it registered 1 kilowatt- 

 hour, or 10 ff worth of current. 



Reading the electric meter, or watt-hour meter (as it is called) 

 is exactly the same as reading the water meter, except that the unit 

 is kilowatt-hours, and the 100,000 circle is missing. Beginning at 

 the right and reading to the left, the circles indicate units, tens, 

 hundreds, thousands. The dial in Figure 20 reads 538 kilowatt- 

 hours. 



Notice that the hand in the tens circle is in a doubtful position. 

 It must be read 30 because the hand in the unit circle has not yet 

 reached 0. (See Caution, Project XXXII.) 



PROJECT LVIII. How to Attach Wires, to a Socket, page 488 



Caution. If you wish to attach a socket to the wiring of your house, 

 be sure to open the switch at the fuse board, thus turning off the cur- 

 rent from your house wires. 



First remove the shell from the cap of the socket (A, Figure 21). 

 If the shell is attached by screws or rivets, turn it to the left and 

 pull it off. If the socket is old, the screws in the cap may have 

 to be loosened. If the shell has a corrugated upper edge that springs 

 into the cap, it may be removed by pressing it firmly near the key 

 (the place is indicated on most shells by the word "Press ") and 

 pulling it out of the cap. 



Notice that the cap and shell are completely lined with insulating 

 material. If the insulating material is missing or damaged, do 

 not use the socket ; it is dangerous. 



Cut off the ends of the two wires even. Remove the insulation 

 from the ends of the wires just far enough back to allow bare wire 

 ends to fit under the attachment screws of the core (A, Figure 21). 

 To do this, cut through the braided cover and scrape off the in- 

 sulation around the wires. In removing this insulation, be very 

 careful not to cut the filaments of wire within. 



When the insulation is removed, roll the exposed filaments of 



