1921] A CONVENIENT THERMOREGULATOR 329 
requires but little explanation. The current passing through the 
regulator and actuating the relay may be taken either from a line 
circuit or from a constant circuit battery. In either case the cur- 
rent should be so reduced by means of resistance and by reduction - 
of the voltage that the current passing through the regulator does 
not exceed 0.015 of an ampere. Larger currents damage the 
regulator. Various types of heaters may be used, but in general 
the current to be interrupted by the relay should be as small as 
possible. Where high temperatures are to be maintained, it is 
usually best to have an auxiliary heater which by running con- 
6 PO/NT-/S000 
OH/T RESISTANCE UNIT. 
70 THERMOREGUTAT OR. 
ANMIFE SHITCH, 
250 OHM TELEGRAPHIC RELAY 
VOAMPERE FUSES, 
70 POWER, 
CARBON LAMPS IN PARALLEL 
WITH RELAY CONTACTS. TOHEATER. 
Fic. 2 
stantly maintains the temperature nearly at the desired point. 
The deficiency is controlled by a heater of smaller capacity regu- 
lated by the relay. If only one heater is employed, a large portion 
of the current may be made to flow continuously by inserting one or 
a number of carbon lamps in the circuit in parallel with the relay. 
The sparking at the relay contacts is thus greatly reduced. It is 
scarcely necessary to state that the relay magnets, armature spring, 
and contact points of the relay should be adjusted very carefully. 
When all adjustments of the installation are perfect, there is 
practically no spark at the relay contacts when the heating current 
is interrupted, and a barely audible click of the armature. it 
proper installation, ordinary telegraphic relays of 250 ohms’ resist- 
ance will break a current of 2 amperes with practically no spark at 
