Geography went hand in hand with travel, Copernican astronomy with
circumnavigation of the globe: and even the theory of evolution and the
historical sciences in the nineteenth century were continuous with liberal
reform: people saw in the past, as they then learned to conceive it,
simply an extension of those transformations which they were witnessing in
the present. They could think they knew the world as a man knows his
native town, or the contents of his chest of drawers: nature was our home,
and science was our home knowledge. For it is not intrinsic clearness or
coherence that make ideas persuasive, but connection with action, or with
some voluminous inner response, which is readiness to act. It is a sense
of on-coming fate, a compulsion to do or to suffer, that produces the
illusion of perfect knowledge.

I call it illusion, although our contact with things may be real, and our
sensations and thoughts may be inevitable and honest; because nevertheless
it is always an illusion to suppose that our images are the intrinsic
qualities of things, or reproduce them exactly. The Ptolemaic system, for
instance, was perfectly scientific; it was based on careful and prolonged
observation and on just reasoning; but it was modelled on an image--the
spherical blue dome of the heavens--proper only to an observer on the
earth, and not transferable to a universe which is diffuse, centreless,
fluid, and perhaps infinite. When the imagination, for any reason, comes
to be peopled with images of the latter sort, the modern, and especially
the latest, astronomy becomes more persuasive. For although I suspect that
even Einstein is an imperfect relativist, and retains Euclidean space and
absolute time at the bottom of his calculation, and recovers them at the
end, yet the effort to express the system of nature as it would appear
from _any_ station and to _any_ sensorium seems to be eminently
enlightening.