Thus we come to know much more about the relations of distances in physical space than about the distances themselves; we may know that one distance is greater than another, or that it is along the same straight line as the other, but we cannot have that immediate acquaintance with physical distances that we have with distances in our private spaces, or with colours or sounds or other sense-data.
[Problems of Philosophy, Bertrand Russell, Chapter III]
I can't imagine what Russell said in the bold text. Could you explain this to me? I think he meant that one distance is parallel to another distance. Is it right?