2 NATURE 
[Atay 5, 1870 
the work—we had almost said the noble work—which 
lies before them. Surely at a time when England would 
gain so much by the scientific education, not only of 
her Workmen but of her Ministers, an attempt to place 
Science before the Public, week by week, as Politics, 
Art, Music, and a hundred other things are placed 
before them, must not be suffered to flag; when the 
number of science-teachers and science-students is 
daily increasing, and the necessity for combined action 
and representation among scientific men themselves 
is being more and more felt, the popularisation of 
science becomes more important than ever, and every 
effort to gain these ends deserves a larger encourage- 
ment, for the most “ practical man” will now soon be 
made to feel that Science dogs his every footstep, 
meets him at every turn, and twines itself round his life ; 
nay, it may soon become evident that such a practical 
thing as a stagnation of trade may in some way be 
traced to the neglect of science. 
Hence our endeavour in the future will be not only 
to make our journal a necessity in the Studies of the 
more thoughtful, and in our Schools, but a welcome 
visitor inthe Homes of all who care for aught that is 
beautiful and true in the world around them. 
EDITOR 
THE VELOCITY OF THOUGHT 
i A® quick as thought” is a common proverb, and pro- 
bably not a few persons feel inclined to regard the 
speed of mental operations as beyond our powers of mea- 
surement. Apart, however, from those minds which take 
their owners so long in making up because they are so 
great, rough experience clearly shows that ordinary think- 
ing does take time ; and as soon as mental processes 
were brought to work in connection with delicate instru- 
ments and exact calculations, it became obvious that the 
time they consumed was a matter for serious considera- 
tion. A well-known instance of this is the “per- 
sonal equation” of the astronomers. When a person 
watching the movement of a star, makes a signal the 
instant he sees it, or the instant it seems to him to crossa 
certain line, it is found that a definite fraction of a second 
always elapses between the actual falling of the image of 
the star on the observer’s eye, and the making of the 
signal—a fraction, moreover, varying somewhat with 
different observers, and with the same observer under 
differing mental conditions. Of late years considerable 
progress has been made towards an accurate knowledge 
of this mental time. 
A typical bodily action, involving mental effort, may be 
regarded as made up of three terms ; of sensations tra- 
velling towards the brain, of processes thereby set up 
within the brain, and of resultant motor impulses tra- 
velling from the brain towards the muscles which are 
about to be used. Our first task is to ascertain how much 
time is consumed in each of these terms; we may after- 
wards try to measure the velocity of the various stages 
and parts into which each term may be further sub- 
divided. 
The velocity of motor impulses is by far the simplest 
case of the three, and has already been made out pretty 
satisfactorily. We can assert, for instance, that in frogs 
a motor impulse, the message of the will to the muscle, 
travels at about the rate of 28 metres a second, while in 
man it moves at about 33 metres. The method by which 
this result is obtained may be described in its simplest 
form somewhat as follows :— 
The muscle which in the frog corresponds to the calf 
of the leg, may be prepared with about two inches of its 
proper nerve still attached to it. Ifa galvanic current be 
brought to bear on the nerve close to the muscle, a motor 
impulse is set up in the nerve, and a contraction of the 
muscle follows. Between the exact moment when the 
current breaks into the nerve, and the exact moment 
when the muscle begins to contract, a certain time 
elapses. This time is measured in this way :—A blackened 
elass cylinder, made to revolve very rapidly, is fitted with 
two delicate levers, the points of which just touch the 
blackened surface at some little distance apart from each 
other. So long as the levers remain perfectly motionless, 
they trace on the revolving cylinder two parallel, hori- 
zontal, unbroken lines ; and any movement of either is in- 
dicated at once by an upward (or downward) deviation 
from the horizontal line. These levers further are so 
arranged (as may readily be done) that the one lever is 
moved by the entrance of the very galvanic current which 
gives rise to the motor impulse in the nerve, and thus 
marks the beginning of that motor impulse; while the 
other is moved by the muscle directly this begins to con- 
tract, and thus marks the beginning of the muscular con- 
traction. Taking note of the direction in which the 
cylinder is revolving, it is found that the mark of the 
setting-up of the motor impulse is always some little 
distance ahead of the mark of the muscular contraction ; 
it only remains to be ascertained to what interval of time 
that distance of space on the cylinder corresponds. Did 
we know the actual rate at which the cylinder revolves 
this might be calculated, but an easier method is to bring 
a vibrating tuning-fork, of known pitch, to bear very 
lightly sideways on the cylinder, above or between the - 
two levers. As the cylinder revolves, and the tuning- 
fork vibrates, the latter will mark on the former a hori- 
zontal line, made up of minute, uniform waves correspond- 
ing to the vibrations. In any given distance, as for 
instance in the distance between the two marks made by 
the levers, we may count the number of waves. These will 
give us the number of vibrations made by the tuning-fork 
in the interval ; and knowing how many vibrations the 
tuning-fork makes in a second, we can easily tell to what 
fraction of a second the number of vibrations counted 
corresponds. Thus, if the tuning-fork vibrates roo times 
a second, and in the interval between the marks of the 
two levers we count ten waves, we can tell that the time 
between the two marks, @.e. the time between the setting- 
up of the motor impulse and the beginning of the muscular 
contraction, was 3/5 of a second. 
Having ascertained this, the next step is to repeat the 
experiment exactly in the same way, except that the 
galvanic current is brought to bear upon the nerve, not 
close to the muscle, but as far off as possible at the 
