the secondary of which is in connexion with the muscle. The
smoked plate receives the traces of the style of the tuning-fork and
of the lever attached to the muscle, and also the trace of an
electromagnetic signal which marks the instant at which the primary
circuit is broken. After the traces are made, they are ruled through
with radial lines, cutting the three traces, and the time intervals
between different parts of the muscle curve are measured in terms of
the period of vibration of the tuning-fork, as in other chronographs
in which the tuning-fork is employed.

Du Bois Reymond.

In the spring myograph of E. Du Bois Reymond (Munk's _Physiologie des
Menschen_, p. 398) a smoked glass plate attached to a metal rod is
shot by a spiral spring along two guides with a velocity which is not
uniform. The traces of a style moved by the muscle under examination,
and of a tuning-fork, are recorded on the glass plate, the shooter
during its traverse knocking over one or more electric keys, which
break the primary circuit of an induction coil, the induced current
stimulating the muscle.

Burch.

In the photo-electric chronograph devised by G.J. Burch, F.R.S.
(_Journ. of Physiology_, 18, p. 125; _Electrician_, 37, p.436), the
rapid movements of the column of mercury in a capillary electrometer
used in physiological research are recorded on a sensitive plate
moving at a uniform angular velocity. The trace of the vibrating
prongs of a tuning-fork of known period is also recorded on the plate,
the light used being that of the electric arc. The images of the
meniscus of the mercury column and of the moving fork are focused on
the plate by a lens. Excellent results have been obtained with this
instrument.

Marey.

An important development of a branch of chronography is due to E.J.
Marey (_Comptes rendus_, 7. aout 1882, and _Le Mouvement_, par E.J.
Marey, Paris, 1894), who employed a photographic plate for receiving
successive pictures of moving objects, at definite times, when
investigating the movements of animals, birds, fishes, insects, and
also microscopic objects such as vorticellae. The instrument in one of
its forms consisted of a camera and lens. In front of the sensitive
plate and close to it a disk, pierced with radial slits, revolved at a
given angular velocity, and each time a slit passed by the plate was
exposed. But since, i