482 ELECTRIC MEASUREMENTS [Cn. XIII 



For the voltmeter. After all the connections for the circuit are 

 complete, connect the two terminals of the voltmeter to any two 

 parts of the line between which it is desired to measure the differ- 

 ence of potential. 



For the ammeter. After all the connections for the circuit are 

 complete, and after the arc has been found to work satisfactorily, 

 cut one of the wires and insert the self-containing ammeter in 

 between the two cut ends just as if it were a short piece of heavy 

 wire. If there is an outside shunt connect the ends of the supply 

 wire to the large binding posts of the shunt and the wires of the 

 ammeter to the smaller binding posts of the shunt. 



669. The Wattmeter. This is an instrument for measuring 

 electrical power or activity. There are two types of wattmeter 

 the portable or indicating wattmeter and the integrating or supply 

 wattmeter. Both work on the same principle, but the method of 

 indication is different. 



The wattmeter has two sets of terminals or binding posts. One 

 set is connected with the line in series along one wire like an 

 ammeter, while the other set is connected in multiple that is, to 

 both lead wires like a voltmeter. In fact this instrument is a 



sort of a combination voltmeter 

 and ammeter, as it measures 

 the product of the volts times 

 the amperes. 



In connecting the wattmeter 

 FIG. 255. WATTMETER TO MEASURE p. rea t care must be taken to ret 

 THE POWER CONSUMED AT THE ARC. 



G Dynamo. the sets of binding posts correct- 



W Wattmeter. ly joined with the line. That is 



R Rheostat. the binding posts for the current 



The heavy line wire passes to the terminals of the wattmeter must 



wattmeter and from it to the upper car- be con nected in series or along 



bon. From the lower carbon the heavy 



wire passes to the rheostat and back one Wire like the ammeter (fig. 

 to the dynamo. The fine wire passes 2 _ 3 ) while the vo l ta ge binding 

 from the upper carbon to the watt- 

 meter, and from the wattmeter to the posts must be connected in para- 

 lower carbon. With this connection of llel or across t he line, like a 

 the wires the power consumed at the 

 arc is measured. voltmeter (fig. 272). 



