August 20, 1885 | 
NATURE 377 
ASTRONOMICAL PHENOMENA FOR THE 
WEEK, 1885, AUGUST 23-29 
(For the reckoning of time the civil day, commencing at 
Greenwich mean midnight, counting the hours on to 24, is here 
employed.) 
At Greenwich on August 23 
Sun rises, 5h. om.; souths, 12h. 2m. 22°7s.; sets, 19h. 5m. ; 
decl. on meridian, 11° 19’ N.: Sidereal Time at Sunset, 
17h. 14m. 
Moon (Full on August 25) rises, 17h. 49m. ; souths, 22h. gom. ; 
sets, 3h. 38m.* ; decl. on meridian, 13° 55’ S. 
Planet Rises Souths Sets Decl. on meridian 
h. m. h. m. h. m. ee 
Mercury ... 6 54 13 I 19 8 o 41N. 
Venus 7 46 13 54 202 o 50N. 
Mars oO 4I 8 56 17 II 23 I8N. 
Jupiter 6 8 I2 50 19 32 7 41 N. 
Saturn o 8 8 17 16 26 22 26N. 
* Indicates that the setting is that of the following day. 
Occultations of Stars by the Moon 
Corresponding 
2 les fi - 
August Star Mag. Disap. Reap, tee cA aaheior 
inverted image 
h. m. h. m. 0 5 
26 ... 67 Aquarii ... 6 iy 9G) 6 9 ... E51 325 
27 ... B.A.C. 8365... 64 ... 20 48 near approach ... 162 — 
The Occultations of Stars are such as are visible at Greenwich. 
August h. 
Cif cae AN 
, 
Mercury in conjunction with and 6° 1 
south of Jupiter. 
THE MOTOR CENTRES OF THE BRAIN AND 
THE MECHANISM OF THE WILL? 
PEELING deeply as I do the responsibility I have incurred 
in undertaking to address you to-night, I desire to express 
my regret that I cannot instead share with you the pleasure of 
listening to the distinguished man who has been prevented by a 
most painful bereavement from addressing you to-night. 
My subject being the mechanism of the will, it might be asked, 
“What has a surgeon to do with psychology?’’ To which I 
would answer, ‘‘ Everything.” For without sheltering myself 
behind Mr. Jonathan Hutchinson’s trite saying that ‘‘a surgeon 
should be a physician who knows how to use his hands,” I 
would remind you that pure science has proved so good a foster- 
mother to surgery, that diseases of the brain which were formerly 
considered to be hopeless, are now brought within a measurable 
distance of the knife, and therefore a step nearer towards cure. 
Again, I would remind you that surgeons rather than physicians 
see the experiments which so-called Nature is always providing 
for us,—experiments which, though horribly clumsy, do on rare 
occasions, as I shall presently show you to-night, lend us power- 
ful aid in attempting to solve the most obscure problems ever 
presented to the scientist. 
The title I have chosen may possibly be objected to as too 
comprehensive ; but until we are ready to admit a new termin- 
ology we must employ the old in order to convey our meaning 
intelligibly, although there may be coupled therewith the risk 
of expressing more than we desire. Thus when I speak of the 
mechanism of the will and the motor centres of the brain, I do 
not intend (as indeed must be obvious) to discuss the existence 
of the so-called freedom of the will, or the source of our con- 
sciousness of voluntary power. 
I shall rather describe to you first the general plan of the 
mechanism which conveys information to our brain, the thinking 
organ ; next the arrangement of those parts in it which are con- 
cerned with voluntary phenomena; and finally I shall seek to 
show by means of experiment that the consciousness of our 
existing as single beings, the consciousness of our possessing but 
one will as people say, while at the same time we know that we 
possess a double nervous system, is due to the fact that pure 
volition is dependent entirely on the exercise of the attention 
which connotes the idea of singleness. Consequently that it is 
impossible to carry out two totally distinct ideas at one and the 
same moment of time, when the attention must of course be 
fully engaged upon each. 
* Lecture at the Royal Institution of Great Britain by Victor Horsley, 
F.R.C.S. 
I fear that in making my argument consecutive, I shall have 
to pass over very well-beaten paths, and so I must ask your 
patience for a few moments while I make good my premisses. 
The nervous system, which in man is composed of brain, 
spinal cord, nerves, and nerve-endings, is arranged upon the 
simplest plan, although the details of the same become highly 
complex when we arrive at the top of the brain. 
At the same time, while we have this simple plan of structure, 
we find that there is also a fundamental mode of action of the 
same—a mode which is a simple exposition of the principle, no 
effect without a cause—a mode of action which is known as the 
phenomenon of simple reflex action. 
The general plan of the whole nervous system is illustrated by 
this model. Imbedded in the tissues all over the body, or 
highly specialised and grouped together in separate organs, such 
as the eye or ear, we find large numbers of nerve-endings,—that 
is, small lumps of protoplasm from which a nerve-fibre leads 
away to the spinal cord and so up to the brain. 
These nerve-endings are designed for the reception of the 
different kinds of vibration by which energy presents itself to us. 
As the largest example of these nerve-endings, let me here show 
you one of the so-called Pacinian bodies, or more correctly, 
Marshall’s corpuscles, for Mr. John Marshall discovered these 
bodies in England before Pacini published his observations in 
Italy. Here you see one of these small oval bodies arranged on 
the ends of one of the nerves of the fingers, and here you see the 
nerve-fibre ending in the little protoplasmic bulb which is pro- 
tected by a number of concentric sheaths. 
Pressure or any form ofirritation of this body at the end of the 
nerve-fibre causes a stream of nerve-energy to travel through the 
spinal cord to the brain, and so we become conscious that some- 
thing is happening to the finger. 
Here in this section of the sensitive membrane of the back of 
the eye, the retina, you see a similar arrangement, only more 
complicated,—namely, nerve-fibres leading away from small 
protoplasmic masses which possess the property of absorbing 
light and transforming it into nerve-energy. It is this trans- 
formation of nerve-energy into heat, light, pressure, &c., which it 
seems to me should alone be called a sensation, irrespective of 
consciousness. And in fact we habitually say we /ee/ a sensation. 
The terms ‘‘ feeling ” and ‘‘sensation,” however, are frequently 
used as interchangeable expressions, although, as I shall show 
you directly, ‘‘ feeling” is the conscious disturbance of a sensory 
centre in the surface of the brain, and in fact feeling is the 
conscious perception of sensations. This distinction between 
feeling and sensation, if dogmatic, will save us from dispute as 
to the meaning of the word ‘‘sensation” ; and further, the dis- 
tinction is one, as I have just shown, which is justified by 
custom. 
Now the nerve fibre which conveys the energy of the sensa- 
tion is a round thread of protoplasm which in all probability 
connects the nerve-ending with a sensory corpuscle in the spinal 
cord. These nerve-fibres running in nerves are white, whereas, 
as you know, protoplasm is gray. They are white because each 
is insulated from its fellow by a white sheath of fatty substance, 
just as we protect telegraph wires with coatings. It is not 
stretching analogy too far to say that nerve-force may probably 
escape unless properly insulated. 
In consequence of the fibres being covered with these white 
sheaths, they form what is called the white matter of the brain ; 
while the nerve centres are grayish, and therefore form what is 
called the grey matter of the brain, so that the grey matter 
receives and records the messages conveyed to it by the white 
insulated fibres. 
From the sensory corpuscle, which is a small mass of proto- 
plasm provided with branches connecting it to neighbouring 
corpuscles, the nerve energy, if adequate, passes along a junction 
thread of protoplasm to a much larger corpuscle, which is called 
a motor corpuscle, and the energy of which, when liberated by 
the nerve impulse from the sensory corpuscle, is capable of ex- 
citing muscles into active contraction. These two corpuscles 
form what is called a nerve centre. 
Not only are the motor corpuscles fewer as well as much 
larger than the sensory ones, but also the nerve fibres which go 
out from them are larger too. In fact it would seem as if we 
had another close analogy to electrical phenomena ; for here, 
where we want a sudden discharge of a considerable intensity of 
nerve force, we find to hand a large accumulator mechanism and 
a large conductor, the resistance of which may justly be supposed 
to be low. Finally, the motor nerve-fibre terminates in a proto- 
plasmic mass which is firmly united to a muscle fibre, and which 
