630 
was eleven syllables a second; and, indeed, at this speed all the 
syllables were not perfectly articulated. J : 
This experiment has no particular interest in itself, for it only 
confirms the results of Schafer, Lovén and Griffiths, that repeated 
voluntary muscular actions have a speed of some ten or twelve per 
second. But, if we modify it slightly, its bearings are much wider. 
If instead of voca//y articulating the syllables, we ¢4z7zk them and 
articulate them only mevdadly, we exclude muscular action from 
any share in the process, and the rapidity of the mental articu- 
lation will be the index of the cerebral rhythm, not the muscular, 
Well, I found, as any of you can do with the help of a good 
seconds watch, that the mental articulation gives exactly the 
same figure as the vocal; that is, ten or eleven syllables per 
second, 
We come to the interesting and relatively unforeseen conclusion 
that the cerebral phenomena of feeling (in the retina), volition 
(on the muscles), and thought (in mental articulation) cannot be 
repeated faster than twelve per second, and that they last about 
one-eleventh, or in round numbers one-tenth, of a second ; the 
isolated sensation, the isolated act of will, the isolated intel- 
lectual process, have all the same minimum duration. 
Placing this result next to our determination of the period of 
the nerve-wave, we conclude that there is here more than a 
mere coincidence ;iit is an @ fosterzort proof of our hypothesis as 
to the period of the nerve-wave. 
From the psychological point of view this leads us to very 
important deductions. Of course we can conceive the second 
to be divided into hundredths, millionths, billionths ; but these 
divisions have no relation to our direct consciousness. Our 
consciousness can only perceive much longer intervals. Our 
cerebral organisation determines narrow limits for our appre- 
ciation of time. We may therefore define the psychological unzt 
of time, the irreducible unit, as that minimum duration of time 
which zs appreciable to our intelligence. This is, indeed, suscep- 
tible of further theoretical subdivision ; but such subdivisions 
correspond to no real mental image. 
We may say, in other words, that the minimum time which 
our consciousness can directly apprehend is, in round numbers, 
one-tenth of a second. 
“* Swift as thought” is an everyday phrase; but you see 
thought is not very swift, after all, if we compare it to the 
enormous frequency of the vibrations of light and electricity. 
Sir William Crookes, one of your most illustrious presidents, 
spoke of the relativity of our knowledge in his recent address ; 
he alluded to the cruel imperfections of our animal nature. 
For us there exists no time-interval shorter than one-tenth 
of a second; and yet during this short interval, within 
which our gross intellectual apparatus cannot penetrate, who 
knows what sequences of phenomena may go on, which we could 
perceive if our nervous system had a shorter period of vibration ? 
Then would phenomena which we perceive as continuous reveal 
their true character of discontinuity ; those molecular vibrations 
which to us do not appear as vibrations would take on their real 
aspects. In a word, our time-unit, which is so different from 
the units of many phenomena of matter, makes us live in one 
perpetual illusion. 
One more point I wish to touch upon is interesting in many 
respects. Let us come back to the diagram I gave you above 
to show the mode of damping of the nerve-wave. I told you 
that the original level is never regained when the system is 
damped toa position of rest ; it approaches the level indefinitely 
but never reaches it. Practically speaking, equilibrium is 
reached at the end of the tenth of a second; physically and 
physiologically speaking, everything is set in order ; the nerve- 
wave is ended, and the return to equilibrium is total. But if 
we deal with infinitesimal quantities this return is not complete ; 
so that if we imagine an apparatus capable of appreciating 
infinitesimal quantities, it would show that, as the mathematical 
theory predicts, the return to equilibrium is never complete or 
absolute. 
Well ! we may fairly suppose that consciousness is alive to 
this infinitely small quantity, and that the impossibility of the 
complete return to the primitive equilibrium accounts for the 
strange phenomenon, unknown in the inorganic world, which 
we call Memory. 
After a nerve-wave, the neuron is no longer in the same 
state as before ; it retains the memory of the wave, and this makes 
it now other than what it was. I pronounce the vowel ‘* A”; 
one-tenth of a second later I can pronounce sone other vowel, 
for my nervous system has returned to equilibrium ; but this 
NO. 1565, VOL. 60] 
NATURE 
[OcToBER 26, 1899 
return, however, is not complete, for the memory of the ‘*A”’ 
which I pronounced persists, and will persist indefinitely. The 
primitive condition will never recur, whatever happens. In 
time the memory of the vowel ‘‘ A” will gradually fade, but it 
will never be effaced. A nerve-wave of the brain is never 
completely extinguished. 
The fact is that we are here on the confines of two totally 
distinct worlds: the world of physics and the world of psych- 
ology. What is infinitesimally small in the physical world may 
possibly be infinitely great in the psychological world. The 
residues of nerve-waves, the asymptotic prolongations of curves, 
may be neglected by the physiologist and the physicist; they 
are not negligible to consciousness. 
Consciousness distinguishes them from the strong vibrations 
actually going on, which it recognises as ‘‘ the present” ; but 
the waves that are passed still exist for consciousness, never 
perhaps to be annihilated. 
Assuredly this is but an hypothesis, perhaps an analogy, a 
comparison, rather than an hypothesis; but it is none the less 
interesting to note how far the physiological theory of the 
damping of the nerve-wave is in agreement with the grand 
psychological fact of memory, which it is scarcely possible to 
explain in any other way. 
IX. 
Thus the nerve-wave in its form and period, and in the 
mode of its damping, is comparable with the various waves of 
the unbounded universe in which we live, move and have our 
being. But this resemblance must not lead us away from the 
recognition of the abyss that separates the nerve-wave from all 
the other phenomena within our reach. The vibrations of the 
forces scattered about us are—at least with the greatest prob- 
ability—blind phenomena, which know not themselves, which 
are the slaves of irresistible fatality. The nerve-wave, on the 
contrary, knows and judges itself; it is self-knowing or self- 
conscious; it can distinguish itself from the world which 
surrounds it and shakes it. 
Since it possesses intelligence—for intelligence and conscious- 
ness are synonymous terms—it is susceptible of perfectibility ; 
it is capable of right reasoning and of wrong reasoning ; it can 
attain a moral ideal forbidden to those brute forces which follow 
their fated course ; it can conceive the idea of truth and justice 
when it is a question of defending the innocent, of establishing 
brotherhood among men. 
Consciousness, intelligence, the making for higher perfection— 
these are characters that have nought in common with the char- 
acters of other waves ; they seem to be phenomena of another, 
a higher order. This vibration, whose physical conditions we 
have studied, enters into the domain of morals ; and this fact 
establishes its essential difference from all other vibrations. 
Assuredly the prodigiously rapid and regular undulations of 
light, and of electricity, appeal right justly to our admiration ; 
but nothing is so admirable as this disturbance of the nerve-cell, 
which is self-knowing, self-judging, self-transforming, which 
strives to amend itself, and which from the stimuli which strike 
it can deduce some of the laws ruling the vast universe distinct 
from it. The nerve-wave of man—himself the last result of 
evolution—is the most perfect term of the things and of the 
beings which it is given to us to know. 
Vast as is the world, mighty as are the fires of the infinite 
stars, the intelligence of man is of a higher order than these ; 
and I would fain exclaim with the great philosopher, Immanuel 
Kant : ‘‘ More than the starry heaven above my head, one thing 
fills me with admiration: the moral law in the heart of man.” 
ZOOLOGY AT THE BRITISH ASSOCIATION. 
@ the opening day (Thursday) only the President’s address 
was taken, and the Section then adjourned with the object 
of hearing addresses in other Sections which were of biological 
interest. The total number of papers brought before the Section 
this year was not as large as usual, but they extended over a 
wide range of zoological subject-matter, as the following outline 
programme shows —— 
Friday morning, morphological papers; Friday afternoon, 
papers on entomology and mimicry ; Saturday, marine biology ; 
Monday, morphology, &c.; Tuesday, papers on sea-fishery 
questions. The usual reports upon investigations in progress 
were also submitted. 
