9 
forces than the latter differ from each other. As a complete 
written history of events may be regarded as a representation of 
them by symbols, arbitrary and not contemporaneous with the 
events, so we may regard simultaneous cerebral and mental states 
as symbols, though not arbitrary, each of the other. To ascer- 
tain what cerebral state corresponds with a given mental state is 
in general an insoluble problem. But in some cases we may 
obtain an approximate solution. External events which affect 
consciousness may be said to be recorded in bilingual inscriptions, 
one part of the record being inscribed on the mind and the other 
on the brain. And the bilingual character of the inscription is 
favorable to interpretation. Thus, the burning the finger is 
recorded bilingually. It is inscribed on the mind in the form of 
a sensation of pain, and on the brain in that of a change 
wrought by a material disturbance propagated thereto from the 
finger. If we could ascertain the cerebral states, corresponding 
to the mental states before and after the feeling of pain, we 
could interpret the physical change in the language of mental 
change. Such interpretations, however, must probably be 
limited in number and variety, and, at all events, it would seem 
vain to anticipate that a knowledge of the laws of mind can be 
obtained by an exclusive study of the phenomena of the living 
body. The material and the mental phenomena must be studied 
separately, and physiology, though it may aid, will not supersede 
psychology. A theory of the evolution of mind cannot be 
estimated in the same way by those who differ from, and those 
who agree with, the psychological, physical, or metaphysical 
views of its author. And some acquaintance with the science of 
mind is necessary to those who approach the subject. But 
uncontested principles of the science are not easily to be found, 
or, at all events, the books are discordant. Excluding all that 
relates to the emotions, and much other matter, how can we 
obtain something like trustworthy information respecting the con- 
stitution of the intellect ? Without going too deeply into metaphy- 
sical questions, which, though they have interested me for between 
thirty and forty years, may not have the same interest for all, 
I think we may obtain it thus : by seeing what views of the 
structure of the mind were taken by a man of recognised genius, 
who, without marked predilection for any particular metaphy- 
sical system, met with acknowledged success in his investigation 
of the operations of the understanding. Such a man was Boole, 
who, otherwise famous in the world of science, gave a new form 
and a wider scope to the science of logic. He notices that such 
questions as the existence of a sustaining ground of phenomena, 
the reality of cause, and others of a like nature, may possess a 
deep interest and significance in relation to science, without 
being essentially scientific ; and that they who believe, and they 
who refuse to believe, that there is more in the relation of cause 
to effect than an unvarying order of succession, agree in their 
interpretation of the conclusions of physical astronomy. He 
asserts that, if the laws which he discusses are really deduced 
