I looked through the eye-piece, also. On a sort of fine grating all I could see was a number of strange lines.
"If you want an opinion from me," I said, with a laugh, "you'll have to tell me first what I am looking at."
"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.