lies in a certain
direction. I arrive at the place. It is thus, that by repeated
experiments I acquire the idea of remote distances.

To confine ourselves however to the question of objects, which without
change of place I can discover by the sense of sight. I can see a town,
a tower, a mountain at a considerable distance. Let us suppose that the
limit of my sight, so far as relates to objects on the earth, is one
hundred miles. I can travel towards such an object, and thus ascertain
by means of my other senses what is its real distance. I can also employ
certain instruments, invented by man, to measure heights, suppose of
a tower, and, by experiments made in ways independent of these
instruments, verify or otherwise the report of these instruments.

The height of the Monument of London is something more than two hundred
feet. Other elevations, the produce of human labour, are considerably
higher. It is in the nature of the mind, that we conclude from the
observation that we have verified, to the accuracy of another, bearing
a striking analogy to the former, that we have not verified. But analogy
has its limits. Is it of irresistible certainty, or is it in fact to
be considered as approaching to certainty, because we have verified
an observation extending to several hundred feet, that an observation
extending to ninety-five millions of miles, or to the incredible
distances of which Herschel so familiarly talks, is to be treated as
a fact, or laid down as a principle in science? Is it reasonable to
consider two propositions as analogous, when the thing affirmed in the
one is in dimension many million times as great as the thing affirmed
in the other? The experience we have had as to the truth of the smaller,
does it authorise us to consider the larger as unquestionable? That
which I see with a bay of the sea or a wide river between, though it
may appear very like something with which I am familiar at home, do I
immediately affirm it to be of the same species and nature, or do I not
regard it with a certain degree of scepticism, especially if, along with
the resemblance in some points, it differs essentially, as for example
in magnitude, in other points? We have a sensation, and we enquire into
its cause. This is always a question of some uncertainty. Is its cause
something of absolute and substantive existence without me, or is it
not? Is its cause something of the very same nature, as the thing that
gave me a similar