as another company of workers of
this period who made an even more direct assault upon the "citadel of
thought." A remarkable school of workers had been developed in Germany,
the leaders being men who, having more or less of innate metaphysical
bias as a national birthright, had also the instincts of the empirical
scientist, and whose educational equipment included a profound knowledge
not alone of physiology and psychology, but of physics and mathematics
as well. These men undertook the novel task of interrogating the
relations of body and mind from the standpoint of physics. They sought
to apply the vernier and the balance, as far as might be, to the
intangible processes of mind.

The movement had its precursory stages in the early part of the century,
notably in the mathematical psychology of Herbart, but its first
definite output to attract general attention came from the master-hand
of Hermann Helmholtz in 1851. It consisted of the accurate measurement
of the speed of transit of a nervous impulse along a nerve tract. To
make such measurement had been regarded as impossible, it being supposed
that the flight of the nervous impulse was practically instantaneous.
But Helmholtz readily demonstrated the contrary, showing that the
nerve cord is a relatively sluggish message-bearer. According to his
experiments, first performed upon the frog, the nervous "current"
travels less than one hundred feet per second. Other experiments
performed soon afterwards by Helmholtz himself, and by various
followers, chief among whom was Du Bois-Reymond, modified somewhat the
exact figures at first obtained, but did not change the general bearings
of the early results. Thus the nervous impulse was shown to be something
far different, as regards speed of transit, at any rate, from the
electric current to which it had been so often likened. An electric
current would flash halfway round the globe while a nervous impulse
could travel the length of the human body--from a man's foot to his
brain.

The tendency to bridge the gulf that hitherto had separated the physical
from the psychical world was further evidenced in the following decade
by Helmholtz's remarkable but highly technical study of the sensations
of sound and of color in connection with their physical causes, in the
course of which he revived the doctrine of color vision which that other
great physiologist and physicist, Thomas Young, had advanced half
a century before. The same t