482 
ELECTRIC MEASUREMENTS 
[Ch. 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 
great care must be taken to get 
the sets of binding posts correct¬ 
ly joined with the line. That is 
the binding posts for the current 
terminals of the wattmeter must 
be connected in series or along 
one wire like the ammeter (fig. 
273) while the voltage binding 
posts must be connected in para¬ 
llel or across the line, like a 
voltmeter (fig. 272). 
Fig. 255. Wattmeter to Measure 
the Power Consumed at the Arc. 
G Dynamo. 
W Wattmeter. 
A Are. 
R Rheostat. 
The heavy line wire passes to the 
wattmeter and from it to the upper car¬ 
bon. From the lower carbon the heavy 
wire passes to the rheostat and back 
to the dynamo. The fine wire passes 
from the upper carbon to the watt¬ 
meter, and from the wattmeter to the 
lower carton. With this connection of 
the wires the power consumed at the 
arc is measured.