in court nowadays, but you probably think the astronomer is one of
the least likely.

"Well, the shadow in this picture can be made to prove an alibi
for someone. Notice. It is seen prominently to the right, and its
exact location on the house is an easy matter. The identification
of the gable casting the shadow ought to be easy. To be exact, I
have figured it out as 19.62 feet high. The shadow is 14.23 feet
down, 13.10 feet east, and 3.43 feet north. You see, I am exact. I
have to be. In one minute it moves 0.080 feet upward, 0.053 feet
to the right, and 0.096 feet in its apparent path. It passes the
width of a weatherboard, 0.37 foot, in four minutes and thirty-
seven seconds."

Kennedy was talking rapidly of data which he had derived from the
study of the photograph as from plumb line, level, compass, and
tape, astronomical triangle, vertices, zenith, pole, and sun,
declination, azimuth, solar time, parallactic angles, refraction,
and a dozen other bewildering terms.

"In spherical trigonometry," he concluded, "to solve the problem
three elements must be known. I know four. Therefore, I can take
each of the known, treat it as unknown, and have four ways to
check my result. I find that the time might have been either three
o'clock, twenty-one minutes and twelve seconds in the afternoon,
or 3:21:31 or 3:21:29, or 3:21:33. The average is 3: 21:26 and
there can be no appreciable error except for a few seconds. I tell
you that to show you how close I can come. The important thing,
however, is that the date must have been one of two days, either
May 22 or July 22. Between these two dates we must decide on