observing your practical application of it. But you spoke just
now of observation and deduction. Surely the one to some extent
implies the other."

"Why, hardly," he answered, leaning back luxuriously in his arm-
chair, and sending up thick blue wreaths from his pipe. "For
example, observation shows me that you have been to the Wigmore
Street Post-Office this morning, but deduction lets me know that
when there you dispatched a telegram."

"Right!" said I. "Right on both points! But I confess that I
don't see how you arrived at it. It was a sudden impulse upon my
part, and I have mentioned it to no one."

"It is simplicity itself," he remarked, chuckling at my
surprise,--"so absurdly simple that an explanation is
superfluous; and yet it may serve to define the limits of
observation and of deduction. Observation tells me that you have
a little reddish mould adhering to your instep. Just opposite
the Seymour Street Office they have taken up the pavement and
thrown up some earth which lies in such a way that it is
difficult to avoid treading in it in entering. The earth is of
this peculiar reddish tint which is found, as far as I know,
nowhere else in the neighborhood. So much is observation. The
rest is deduction."

"How, then, did you deduce the telegram?"

"Why, of course I knew that you had not written a letter, since I
sat opposite to you all morning. I see also in your open desk