His examination of the looted library was minute, taking in the window through which the thief had apparently entered, the cabinet he had forced, and the situation in general.  Finally Craig set up his camera with most particular care and took several photographs of the window, the cabinet, the doors, including the room from every angle.  Outside he snapped the two sides of the corner of the house in which the library was situated.  Partly by trolley and partly by carriage we crossed the island to the south shore, and finally found McLoughlin’s farm where we had no trouble in getting half a dozen photographs of the porch and house.  Altogether the proceedings seemed tame to me, yet I knew from previous experience that Kennedy had a deep laid purpose.

We parted in the city, to meet just before it was time to visit Miss Ashton.  Kennedy had evidently employed the interval in developing his plates, for he now had ten or a dozen prints, all of exactly the same size, mounted on stiff cardboard in a space with scales and figures on all four sides.  He saw me puzzling over them.

“Those are metric photographs such as Bertillon of Paris takes,” he 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 itself.  Bertillon has 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 the portrait parle, finger prints, and the rest.

“For instance, 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 several peculiar things that I observed to-day, and I have here an indelible record of the scene of the crime.  Preserved in this way it cannot be questioned.

“Now the photographs were in this cabinet.  There are other cabinets, but none of them has been disturbed.  Therefore the thief must have known just what he was after.  The marks made in breaking the lock were not those of a jimmy but of a screwdriver.  No amazing command of the resources of science is needed so far.  All that is necessary is a little scientific common sense, Walter.