APPLICATIONS OF THE GRAPHIC METHOD. 175 
there be equally exact methods of applying, regulating, and 
measuring the stimulus that induces the contraction. 
Fig. 170 gives a representation of the inductorium of Du 
Bois-Reymond, by which either a single brief stimulation or a 
Fig. 170.—Du Bois-Reymond’s inductorium (after Rosenthal). 7, secondary coil; c, primary 
coil ; b, electro-magnet ; h, armature of hammer ; f, small movable screw. The current 
from battery, ascending metal pillar, passes along hammer, and by screw gets into primary 
coil, thus inducing current in secondary coil. By connection between primary coil and 
wires around soft iron of b, iron becomes a magnet, hammer is attracted from screw f, 
and current thus broken ; but when this occurs, soft iron ceases to be a magnet neces- 
sarily, and, hammer Sprineine back, the whole course of events is repeated. This may 
occur several hundred timesinasecond. The above may be clearer from diagram, Fig. 
171. By sliding secondary coil up and down, strength of induced current can be graduated, 
series of such repeated with great regularity and frequency 
may be effected. The apparatus consists essentially of a pri- 
Fic, 171.—Diagrammatic representation of the working of Fig. 170 (after Rosenthat). 
