But when our sleep is imperfect, as when we have determined to rise in half
an hour, time appears longer to us than in most other situations. Here our
solicitude not to oversleep the determined time induces us in this
imperfect sleep to compare the quick changes of imagined scenery with the
parts of time or place, they would have taken up, had they real exigence;
and that more frequently than in our waking hours; and hence the time
appears longer to us: and I make no doubt, but the permitted time appears
long to a man going to the gallows, as the fear of its quick lapse will
make him think frequently about it.

13. As we gain our knowledge of time by comparing the present scenery with
the past and future, and of place by comparing the situations of objects
with each other; so we gain our idea of consciousness by comparing
ourselves with the scenery around us; and of identity by comparing our
present consciousness with our past consciousness: as we never think of
time or place, but when we make the companions above mentioned, so we never
think of consciousness, but when we compare our own existence with that of
other objects; nor of identity, but when we compare our present and our
past consciousness. Hence the consciousness of our own existence, and of
our identity, is owing to a voluntary exertion of our minds: and on that
account in our complete dreams we neither measure time, are surprised at
the sudden changes of place, nor attend to our own existence, or identity;
because our power of volition is suspended. But all these circumstances are
more or less observable in our incomplete ones; for then we attend a little
to the lapse of time, and the changes of place, and to our own existence;
and even to our identity of person; for a lady seldom dreams, that she is a
soldier; nor a man, that he is brought to bed.

14. As long as our sensations only excite their sensual motions, or ideas,
our sleep continues sound; but as soon as they excite desires or aversions,