"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.