104 ROYAL SOCIETY OF CANADA 
The latter swings to one side, completes the relay circuit at b, thus 
operating the solenoid Z and (by reason of the cord) breaking the & 
solenoid circuit. In consequence the pointer (oscillating through one 
division of the dial) indicates directly the “minimum E.M.F. for electro- 
lysis.” 
To MEASURE TIME. 
With the sign block “ Hundredth minutes” (17, 23; 20, 24) in 
position, the instrument acts as a stop watch. The pointer is set in 
motion when contact is made between the terminals, and stops immedi- 
ately the contact is broken. The speed of the motor can be adjusted 

Big. LX. 
(rheostat and speed indicator) so that the pointer moves over the dial 
from 0 to 100 in one minute. 
The momentum of the fly wheel is so great, and the friction of the 
resistance wheel ( W ) on its bearings so slight, that no appreciable differ- 
ence in rate is caused by bringing the solenoid into operation. 
To MEASURE TEMPERATURE. 
As the electrical resistance of copper is a linear function of the 
temperature, it is only necessary to express the resistance of a coil of 
copper wire in suitable units in order to have its temperature in degrees 
centigrade. 
This may be effected by connecting in series with the wheel a 
stationary coil, the resistance of which (about 500 ohms) depends on the 
temperature coefficient of the wire employed as a thermometer, 

