BOOK I PART IV
which distinguishes them from the impres-
sions, whose existence depends upon our per-
ception. Those mountains, and houses, and
trees, which lie at present under my eye, have
always appeared to me in the same order; and
when I lose sight of them by shutting my eyes
or turning my head, I soon after find them re-
turn upon me without the least alteration. My
bed and table, my books and papers, present
themselves in the same uniform manner, and
change not upon account of any interruption in
my seeing or perceivilng them. This is the case
with all the impressions, whose objects are sup-
posed to have an external existence; and is the
case with no other impressions, whether gentle
or violent, voluntary or involuntary.
This constancy, however, is not so perfect as
not to admit of very considerable exceptions.