APPLICATIONS OF THE GRAPHIC METHOD. 173 
little mass of steel attached to it, the whole working in unison 
with the tuning-fork, so that an interruption of the current 
Fie. 166.—Marey’s pp ees as applied to revolving cylinder (after McKendrick). a, gal- 
vanic element ; 6, wooden stand bearing tuning-fork (two hundred vibrations per second); 
c, electro-magnet between limbs of tuning-fork ; d, e, positions for tuning-forks of one hun- 
dred and fifty vibrations per second ; f, tuning-fork lying loose, which may be applied to 
d; g, revolving cylinder ; h, electric chronograph kept in vibration synchronous with the 
tuning-fork interrupter. The current working the electro-magnet from a is interrupted at 
. Foucault's regulator is seen over the clock-work of the cylinder, a little to the right 
of g. 
implies a like change of position of the writing-style, which is 
always kept in contact with the recording surface. 
Fig. 167.,—Side view of Marey’s chronograph (after McKendrick). a, a, coils of wire ; b, b, 
keepers of electro-magnets ; c, vibrating style fixed to the steel plate e; d, binding screws 
for attachment of wires ; + from interrupting tuning-fork ; — to the battery. 
Fig. 177 shows the arrangements for recording a single 
muscle contraction, and Fig. 178 the character of the tracing 
obtained. 
A muscle-nerve preparation, which usually consists of the 
gastrocnemius of the frog with the sciatic nerve attached, 
