ave no revelation, at least on the subject of astronomy,
and of the unnumbered inhabitable worlds that float in the ocean of
ether; and we are bound therefore to sail, as the mariners of ancient
times sailed, always within sight of land. One of the earliest maxims of
ordinary prudence, is that we ought ever to correct the reports of one
sense by the assistance of another sense. The things we here speak of
are not matters of faith; and in them therefore it is but reason, that
we should imitate the conduct of Didymus the apostle, who said, "Except
I put my fingers into the prints of the nails, and thrust my hand into
his side, I will not believe." My eyes report to me an object, as having
a certain magnitude, texture, and roughness or smoothness; but I require
that my hands should confirm to me the evidence of my eyes. I see
something that appears to be an island at an uncertain distance from
the shore; but, if I am actuated by a laudable curiosity, and wish to
possess a real knowledge, I take a boat, and proceed to ascertain by
nearer inspection, whether that which I imagined to be an island is an
island or no.

There are indeed many objects with which we are conversant, that are
in so various ways similar to each other, that, after having carefully
examined a few, we are satisfied upon slighter investigation to admit
the dimensions and character of others. Thus, having measured with a
quadrant the height of a tower, and found on the narrowest search and
comparison that the report of my instrument was right, I yield credit to
this process in another instance, without being at the trouble to verify
its results in any more elaborate method.

The reason why we admit the inference flowing from our examination
in the second instance, and so onward, with less scrupulosity and
scepticism than in the first, is that there is a strict resemblance and
analogy in the two cases. Experience is the basis of our conclusions and
our conduct. I strike against a given object, a nail for example, with
a certain degree of force, because I have remarked in myself and others
the effect of such a stroke. I take food and masticate it, because I
have found that this process contributes to the sound condition of my
body and mind. I scatter certain seeds in my field, and discharge the
other functions of an agriculturist, because I have observed that in due
time the result of this industry is a crop. All the propriety of these
proceedings depends u