STUDIES OF MATTER AND LIFE. 
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traces of a beginning, discover no symptoms of an end. There 
is an eternal flow and motion throughout the universe, a cease- 
less change from power in the potential to power in the active 
form, and back again from the active to the potential — nothing 
added, nothing stationary, and nothing lost. Such is the aspect 
of the physical world, but what of the world of thought and 
will ? Here we pause before a door of difficulty, and have no 
key to open. Let Du Bois-Reymond point it out : — 
“ Suppose we had arrived at an astronomical knowledge of 
the human brain, or even of an analogous organ in an inferior 
creature whose intellectual activity was limited to the sensa- 
tions of well-being and discomfort. So far as regards the 
material phenomena of the brain our comprehension would be 
perfect, and our intellectual need to seek for causes would be 
satisfied in the same degree as it would be in regard to con- 
traction and secretion, if we possessed astronomical knowledge 
of a muscle and a gland. The involuntary acts which emanate 
from nervous centres, without being necessarily connected with 
sensations, such as reflex and associated movements, respiration, 
tonicity, and lastly, the nutrition of the brain and spinal mar- 
row, would be entirely known to us. It would be the same with 
the material changes that always coincide with intellectual 
phenomena, and which probably are conditions indispen- 
sable to them. And surely it would be a great triumph of 
science if we could affirm that such intellectual pheno- 
menon was accompanied with certain movements of atoms 
in certain ganglionic cells and certain nerve tubes. What 
could be more interesting than to direct our intellectual 
vision inwards, and see the cerebral mechanism in motion 
corresponding with an operation of arithmetic, as we can watch 
that of a calculating machine ; or to perceive what rhythmical 
movement of the atoms of carbon, hydrogen, nitrogen, oxygen, 
phosphorus, &c., corresponds with the pleasure we feel from 
musical harmony; what eddying currents of the like atoms 
attend the acme of delight, and what molecular tempests accom- 
pany the horrible suffering that ensues from irritation of the 
trigerminal nerve . . . ; but as regards the mental phenomena 
themselves, it is easy to see that, after acquiring an astronomical 
knowledge of the brain, they would remain just as incompre- 
hensible as they are now. In spite of such knowledge, we 
should be arrested by those phenomena as things that are in- 
commensurable. The most intimate knowledge of the brain to 
which we can aspire would only reveal to us matter in move- 
ment ; but no arrangement, and no movement of material par- 
ticles, can form a bridge to conduct us into the domain of 
intelligence. Motion can produce nothing but motion, or enter 
into the condition of potential energy. Potential energy in its 
