produced by the sphygmograph, which I have used in other cases up
to this time, are clumsy and inexact."

Again he paused as if to let the fear of discovery sink deep into
the minds of all of us.

"This current, as I have said, passes from each one of you in turn
over a wire and vibrates a fine quartz fibre up there in unison
with each heart here. It is one of the most delicate bits of
mechanism ever made, beside which the hairspring of a watch is
coarse. Each of you in turn, is being subjected to this test. More
than that, the record up there shows not only the beats of the
heart but the successive waves of emotion that vary the form of
those beats. Every normal individual gives what we call an
'electro-cardiogram,' which follows a certain type. The
photographic film on which this is being recorded is ruled so that
at the heart station Dr. Barron can read it. There are five waves
to each heart-beat, which he letters P, Q, R, S, and T, two below
and three above a base line on the film. They have all been found
to represent a contraction of a certain portion of the heart. Any
change of the height, width, or time of any one of those lines
shows that there is some defect or change in the contraction of
that part of the heart. Thus Dr. Barron, who has studied this
thing carefully, can tell infallibly not only disease but
emotion."

It seemed as if no one dared look at his neighbour, as if all were
trying vainly to control the beating of their own hearts.

"Now," concluded Kennedy solemnly as if to force the last secret