330 BOTANICAL GAZETTE [APRIL 
the contacts. For larger currents it is better to use some form of 
solenoid control switch actuated by the relay. 
The installation shown in fig. 2 is adapted for a direct current 
circuit. In this case the current for the relay magnets is taken from 
the line as shown. If alternating current only is available, the 
current for actuating the relay should be supplied by a suitable 
constant circuit battery. Dry cells may be used if the current is on 
only for comparatively short intervals. In either case the current 
should not exceed 0.015 of an ampere. If an alternating current 
is used in the heating circuit, the condenser is not necessary, the 
reduction of the spark in that case being effected by the lamps alone. 
The regulators were constructed by Henry J. GREEN, of 
Brooklyn, New York, to whom I am indebted for interest and 
cooperation in perfecting the instrument. 
BurEAvu OF PLant INDUSTRY 
WaAsHINGTON, D.C. 
