160 
POPULAR SCIENCE REVIEW. 
turn can produce nothing besides motion, the maintenance of 
an equilibrium, the exertion of pressure on traction. The total 
quantity of energy remains always the same. In the material 
world nothing can go beyond this law, and nothing can do less 
than it requires. The mechanical effect is precisely equal to 
the mechanical cause that exhausts itself in producing it. Thus 
the intellectual phenomena which flow from the brain beside of, 
but in addition to, the material changes that occur in it, are, 
to our intelligence, wanting in a sufficient reason. These phe- 
nomena remain outside the physical law of causality, and that 
is sufficient to render them incomprehensible.” * 
Du Bois-Reymond, " Revue Scientifique,” Oct. 10, 1874, p. 342. 
