mounted on stiff cardboard in a space with scales and figures on
all four margins. Carton and I puzzled over them.

"Those are metric photographs, such as Bertillon of Paris used to
take," Craig explained. "By means of the scales and tables and
other methods that have been worked out, we can determine from
those pictures distances and many other things almost as well as
if we were on the spot ourselves. Bertillon cleared up many crimes
with this help, such as the mystery of the shooting in the Hotel
Quai d'Orsay and other cases. The metric photograph, I believe,
will in time rank with other devices in the study of crime."

He was going over the photographs carefully.

"For instance," he continued, "in order to solve the riddle of a
crime, the detective's first task is to study the scene
topographically. Plans and elevations of a room or house are made.
The position of each object is painstakingly noted. In addition,
the all-seeing eye of the camera is called into requisition. The
plundered room is photographed, as in this case. I might have done
it by placing a foot rule on a table and taking that in the
picture. But a more scientific and accurate method has been
devised by Bertillon. His camera lens is always used at a fixed
height from the ground and forms its image on the plate at an
exact focus. The print made from the negative is mounted on a card
in a space of definite size, along the edges of which a metric
scale is printed. In the way he has worked it out, the distance
between any two points in the picture can be determined. With a
topographical plan and a metric photograph one can study a crime,
as a general studies the map of a strange country. There were