210 



ELEMENTS OF GENERAL SCIENCE 



In figure 102 the dials for an ordinary watt-hour meter are 

 shown. In the meters in most common use there are figures 

 above or below each dial to indicate the value of a complete 

 rotation of the pointer on that dial. If there are ten divi- 

 sions on the dial, each division is one tenth of the value of the 

 number near the dial. Some of the pointers rotate clockwise 



and some counter- 

 clockwise, and the 

 direction must be 

 noted in each case. 

 One revolution of 

 the pointer on any 

 right-hand dial is 

 equal in value to 

 one-tenth revolu- 

 tion on the dial 

 next to it on the 

 left. Sometimes a 

 multiplying num- 

 ber is given, in 

 which case the ac- 

 tual reading must 



be SO multiplied to 

 dpfpr^np +}, nnr 



rect Values. Finally, 



the reading last 



made must be obtained and deducted from the present read- 

 ing in order to show the correct amount of energy used since 

 the last reading. The following example will show how the 

 cost is computed : 



Reading (present month) = 9121 kilowatt hours 



Reading (last month) = 9101 kilowatt hours 



Difference = 20 kilowatt hours 



20 kilowatt hours at 10 cents per kilowatt hour = $2. The bill for 

 the month is $2. 



flatiron 



The resistance wire shown in the iron is heated by 



the current. Devices are also shown for attaching the 



cord for use of a lamp, for turning the current on and 



off, and for attaching fuse plugs 



