"
"That," he explained, 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 defraction spectroscopes.
"Every substance, you know, is, when radiating light,
characterized by what at first appears to be almost haphazard sets
of spectral bands 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, looking up at me with a twinkle in his
eye, "I wish that 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 carried it in my arms to the laboratory with
some profanity and many scratches.
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