anged from mere aversion at being gazed at, all the way to the
subjective development of real physical illness out of otherwise
trifling ailments. If not that, what object could there be for anyone to
cause such a condition? Might it be for the purpose of robbery? Or might
it be for revenge?

Back in the laboratory, Kennedy pulled out from a cabinet a peculiar
apparatus. It seemed to consist of a sort of triangular prism set with
its edge vertically on a rigid platform attached to a massive stand.

Next he lighted one of the cigarette stubs which he had carried away so
carefully. The smoke curled up between a powerful light and the peculiar
instrument, while Craig peered through a lens, manipulating the thing
with exhaustless patience and skill.

Finally he beckoned me over and I looked through, too. On a sort of fine
grating all I could see was a number of strange lines.

"That," he explained in answer to my unspoken question as I continued to
gaze, "is one of the latest forms of the spectroscope, known as the
interferometer, with delicately ruled gratings in which power to resolve
the straight close lines in the spectrum is carried to the limit of
possibility. A small watch is delicate, but it bears no comparison to
the delicacy of these detraction spectroscopes.

"Every substance, you know, is, when radiating light, characterized by
what at first appears to be almost a haphazard set of spectral lines
without relation to one another. But they are related by mathematical
laws and the apparent haphazard character is only the result of our lack
of knowledge of how to interpret the results."

He resumed his place at the eye-piece to check over his results.
"Walter," he said finally with a twinkle of the eye, "I wish you'd go
out and find me a cat."

"A cat?" I repeated.

"Yes--a cat--felis domesticus, if it sounds better that way, a plain
ordinary cat."

I jammed on my hat and, late as it was, sallied forth on this apparently
ridiculous mission.

Several belated passers-by and a policeman watched me as though I were a
house-breaker and I felt like a fool, but at last by perseverance and
tact I managed to capture a fairly good specimen of the species and
transported it in my arms to the laboratory without an undue number of
scratches.

CHAPTER XXXVI

THE WEED OF MADNESS

In my absence Craig had set to work on a peculiar apparatus, as though
he were distilling something from several of the other cig