t was just a funny closed curve, having neither
mathematical nor structural significance. Maybe he was going crazy!

He threw the curve down on his desk and, soothed by the whirring of
the tracer motor, fell into a brown study. Suddenly, the image of the
brunette with the violet eyes appeared. No reclining nude, she; she
shook her head in that habitual gesture and her long bob fell
perfectly in place. She turned, with demurely downcast lashes and
looked up at him with her violet eyes, and Norm came out of his trance
with a start.

He removed the last curve--a simple hyperbolic curve, probably a
problem in attenuation or decay of some kind--and put in the last
punch-card. The machine started up immediately; the curve was
elliptical. Then a vertical down-stroke, retraced and with a gentle
half-loop added. It was writing! P-r-o-p-i-n-q.... What might this be?
He watched, fascinated, as the letters continued. "Propinquity is the
mother of love," it said, and stopped.

His trained mathematical logic gave him an immediate solution to the
enigma: he was cracking up. It was utterly impossible to derive the
equation to write "propinquity" in Spencerian script in less than a
hundred man-hours, nor could a mathematical calculator be hired for so
frivolous a purpose. It was fantastic, impossible; therefore, it was
not so, and he was either dreaming or crazy. Maybe thinking about that
little brunette.... Surely not; still, he had been driving himself
pretty hard. In the morning he would be fresh and alert. If it were a
trick, he'd catch the trickster. And if it turned out to be a
perfectly logical curve, he'd see a doctor.

He left the curve in the machine, closed the ventilator in the wall
over his desk, and turned on the burglar alarm. This was nothing so
crude as a loose board with a switch, but a quite elaborate electronic
circuit that produced a field near the door. It wouldn't work on
ghosts, but if any material body entered that field, it would trip the
alarm and start a regular Mardi Gras. Security required by government
contracts hardly demanded so much, but for a small plant it was
sufficiently cheap, and Charley had had a lot of fun with it. Charley!
Have to keep him out, too; and being its daddy, he'd know how to
disable the alarm. Of course, it would really be sufficient to tie a
thread across the door which would break if anyone entered. He had no
thread, but after a moment's thought, he pulled a three-cent stamp o