now?"

The three strips of triple exposures were taken to the dark room and
developed by the camera man. They were dried on the revolving electric
drums, near a battery of fans. Shirley studied every step of the work,
with this and that question--this had been his method of acquiring a
curiously catholic knowledge of scientific methods since leaving the
university, where sporting proclivities had prompted him to slide
through courses with as little toil as possible.

A print upon "positive" film was made from each: every strip was
duplicated twenty-five times, at Shirley's suggestion. Then after two
hours of effort the material was ready to be run through the projecting
machine, for viewing upon the screen.

The manager led Shirley to the small exhibition theatre in which every
film was studied, changed and cut from twenty to fifty times before
being released for the theatres. The camera man went into the little
fire-proof booth, to operate the machine.

"Which one first, chief?"

"Take one by chance," said Shirley, "and I will guess its number. Start
away."

There was a flare of light upon the screen, as the operator fussed with
the lamp for better lumination. He slowly began to turn the crank, and
the criminologist watched the screen with no little excitement. The
picture thrown up resembled nothing so much as three endless snakes
twisting in the same general rhythm from top to bottom of the frame. The
twenty-five duplicates were all joined to the original, so that there
was ample opportunity to compare the movements.

"Well, gov'nor, which film was that?" asked the operator.

"Not A--it was B or C!"

"Correct. How'd you guess it? Which is this one?"

As he adjusted another roll of film in the projector, Shirley turned to
the manager sitting at his side. "Mr. Harrison, were those snakes all
exactly alike?"

"No. They all wriggled in the same direction, at the same time. But
little rough angles in some movements and queer curves in others made
each individually different."

"Just what I thought. There goes another.--That is not film A, either!"

"Righto!" confirmed the camera man. As the detailed divergence between
the lines became more evident in the repetitions, Shirley slapped his
knee.

"Now for the finish. Try reel A."

This time the three snakey lines moved along in almost identical
synchronism. The only difference was that the first was thin, the second
heavier, the third the darkest and mos