observation, which recent chemical and physical inquirers have found
indispensable for the establishment of their results. We cannot,
therefore, be surprised that mental philosophers, dealing with facts
even more obscure, and careless about enlarging, varying,
authenticating their records of particular facts, should have had
little success in establishing any results at all.

But if even those, who adopt the psychological theory, have been remiss
in the observation of particular mental facts,--those who deny the
theory have been far more than remiss; they have been blind to obvious
facts contradicting the principles which they lay down. Mr Mill, in
chap, xiv., deals with this denial, common to Mr Mansel with Sir W.
Hamilton. That philosophers so eminent as both of them should declare
confidently--'what I cannot but think must be _à priori_, or original to
thought; it cannot be engendered by experience upon custom' (p.
264)--appears to us as extraordinary as it does to Mr Mill. Though no
one ever surpassed Sir W. Hamilton in large acquaintance with the actual
diversities of human belief, and human incapacities of believing--yet he
never seems to have thought of bringing this acquaintance into account,
when he assured the students in his lecture-room, that custom,
experience, indissoluble association, were altogether insufficient to
engender a felt necessity of believing. Such forgetfulness of well-known
mental facts cannot be reproached to the advocates of the psychological
theory.

In chap. xv. Mr Mill examines Sir W. Hamilton's doctrine on unconscious
mental modifications. He points out the confused manner in which Sir W.
Hamilton has conceived _mental latency_, as well as the inconclusive
character of the reasoning whereby he refutes the following doctrine of
Dugald Stewart--That in the most rapid trains of association, each