276 A. BOYD. 
Fig.8. 
BB, battery, K,Kz, keys. T, tuningfork. P, platinum wire dipping 
into mercury. S,Se, electromagnets with styluses. M, make and break. 
C, connection to bed-plate. 
from the magnet when the circuit is open. Rigidly attached 
to the armature is a stiff stylus, which presses upon smoked 
paper wrapped rounda drum capable of rotation. The axis 
of this drum is a screw, which is borne on a stand; when 
the handle of the drum is turned, the drum rotates and at’ 
the same time moves longitudinally, thus allowing a con- 
tinuous record. In the other circuit is a tuning fork T, 
which makes 100 vibrations per second, as determined by 
comparison with a standard Konig fork making 50 vibra- 
tions per second, and an electromagnet with its stylus as 
before. The current in this circuit is made and broken by 
a piece of platinum wire which dips into a bath of mercury 
at P. The mercury bath must be covered by a stream of 
alcohol in order to keep it clean. Between the arms of the 
