Charles Babbage.

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I soon perceived that a lighthouse, whose number was continually
repeated with a blink, obscuring just half its light, would be seen
_without any blink_ at all distances beyond half its range; but that
at all distances within its half range that fact would be indicated by
a blink. Thus with two blinks, properly adjusted, the distance of a
vessel from a first-class light would be distinguished at from twenty
to thirty miles by occultations indicating its number without any
blink; between ten and twenty miles by an occupation with one blink,
and within ten miles by an occultation with two blinks.

But another advantage was also suggested by this defect. {455} If the
opaque cylinder which intercepts the light consists of two cylinders, A
and B, connected together by rods: thus—

If the compound cylinder descend to _a_, and then rise again, there
will be a single occultation.

If the compound cylinder descend to _b_, and then rise again, there
will be a double occultation.

If the compound cylinder descend to _c_, and then rise again, there
will be a triple occultation.

Such occultations are very distinct, and are specially applicable to


In the year 1851, during the Great Exhibition, the light I have
described was exhibited from an upper window of my house in Dorset
Street during many weeks. It had not passed unnoticed by foreigners,
who frequently reminded me that they had passed my door when I was
asleep by writing upon their card the number exhibited by the occulting
light and dropping it into my letter-box.

About five or six weeks after its first appearance I received a letter
from a friend of mine in the United States, expressing great interest
about it, and inquiring whether its construction was a secret. My
answer was, that I made no {456} secret of it, and would prepare and
send him a short description of it.

I then prepared a description, of which I had a very few copies
printed. I sent twelve of these to the proper authorities of the
great maritime countries. Most of them were accompanied by a private
note of my own to some person of influence with whom I happened to be

One of these was addressed to the present Emperor of the French, then a
member of their Representative Chamber. It was dated the 30th November,
1852. Three days after I read in the newspapers the account of the
_coup_ of December 2, and smiled at the inopportune time at which my
letter had accidentally been forwarded. However, three days after
I received from M. Mocquard the prettiest note, saying that he was
commanded by the Prince President to thank me for the communication,
and to assure me that the Prince was as much attached as ever to
science, and should always continue to promote its cultivation.


The letter which was sent to the United States was placed in the hands
of the Coast Survey. The plan was highly approved, and Congress made
a grant of 5,000 dollars, in order to try it experimentally. After a
long series of experiments, in which its merits were severely tested, a
report was made to Congress strongly recommending its adoption. I then
received a very pressing invitation to visit the United States, for
the purpose of assisting to put it in action. It was conveyed to me by
an amiable and highly cultivated person, the late Mr. Reed, Professor
of English Literature at Philadelphia, who, on his arrival in London,
proposed that I should accompany him on his return in October, the best
season for the voyage, and in the finest vessel of their mercantile
navy. I had long had a great wish to visit the American continent, but
I did {457} not think it worth crossing the Atlantic, unless I could
have spent a twelvemonth in America. Finding this impossible under the
then circumstances, about a month before the time arrived I resigned
with great reluctance the pleasure of accompanying my friend to his own


It was most fortunate that I was thus prevented from embarking on board
the Arctic, a steamer of the largest class.

Steaming at the rate of thirteen knots an hour over the banks of
Newfoundland during a dense fog, the Arctic was run into by a steamer
of about half its size, moving at the rate of seven knots. The
concussion was in this instance fatal to the larger vessel.

This sad catastrophe was thus described by the brother of my lost

“On the 20th of September, 1854, Mr. Reed, with his sister, embarked
at Liverpool for New York, in the United States steamship Arctic.
Seven days afterwards, at noon, on the 27th, when almost in sight of
his native land, a fatal collision occurred, and before sundown every
human being left upon the ship had sunk under the waves of the ocean.
The only survivor who personally acquainted with my brother, saw
him about two o’clock, P.M., after the collision, and not very long
before the ship sank, sitting with his sister in the small passage
aft of the dining-saloon. They were tranquil and silent, though their
faces wore the look of painful anxiety. They probably afterwards left
this position, and repaired to the promenade deck. For a selfish
struggle for life, with a helpless companion dependent upon him, with
a physical frame unsuited for such a strife, and above all, with a
sentiment of religious resignation which taught him in that hour of
agony, even with the memory of his wife and children thronging in his
mind, to bow his head in {458} submission to the will of God,—for such
a struggle he was wholly unsuited; and his is the praise, that he
perished with the women and children.”


In 1853 I spent some weeks at Brussels. During my residence in that
city a Congress of naval officers from all the maritime nations
assembled to discuss and agree upon certain rules and observations to
be arranged for the common benefit of all. One evening I had the great
pleasure of receiving the whole party at my house for the purpose of
witnessing my occulting lights.

The portable occulting light which I had brought with me was placed in
the verandah on the first floor, and we then went along the Boulevards
to see its effect at different distances and with various numerical
signals. On our return several papers relating to the subject were
lying upon the table. The Russian representative, M. ———, took up one
of the original printed descriptions and was much interested in it. On
taking leave he asked, with some hesitation, whether I would lend it
to him for a few hours. I told him at once that if I possessed another
copy I would willingly give it to him; but that not being the case I
could only offer to lend it. M. ——— therefore took it home with him,
and when I sat down to breakfast the next morning I found it upon my
table. In the course of the day I met my Russian friend in the Park. I
expressed my hope that he had been interested by the little tract he
had so speedily returned. He replied that it had interested him so much
that he had sat up all night, had copied the whole of it, and that his
transcript and a despatch upon the subject was now on its way by the
post to his own Government.

Several years after I was informed that _occulting solar lights_ {459}
were used by the Russians during the siege of Sebastopol.

_Night Signals._

The system of occulting light applies with remarkable facility to night
signals, either on shore or at sea. If it is used numerically, it
applies to all the great dictionaries of the various maritime nations.
I may here remark, that there exist means by which all such signals
may, if necessary, be communicated in cipher.

_Sun Signals._

The distance at which such signals can be rendered visible exceeds
that of any other class of signals by means of light. During the Irish
Trigonometrical Survey, a mountain in Scotland was observed, with an
angular instrument from a station in Ireland, at the distance of 108
miles. This was accomplished by stationing a party on the summit of
the mountain in Scotland with a looking-glass of about a foot square,
directing the sun’s image to the opposite station. No occultations were
used; but if the mirror had been larger, and occultation employed,
messages might have been sent, and the time of residence upon the
mountain considerably diminished. When I was occupied with occulting
signals, I made this widely known. I afterwards communicated the plan,
during a visit to Paris, to many of my friends in that capital, and, by
request, to the Minister of Marine.

I have observed in the “Comptes Rendus” that the system has to a
certain extent been since used in the south of Algeria, where, during
eight months of the year, the sun is generally unobscured by clouds
as long as it is above the horizon. I have not, however, noticed in
those communications to the Institute any reference to my own previous
publication. {460}

_Zenith-light Signals._

Another form of signal, although not capable of use at very great
distances, may, however, be employed with considerable advantage,
under certain circumstances. Universality and economy are its great
advantages. It consists of a looking-glass, making an angle of 45°
with the horizon, placed just behind an opening in a vertical board.
This being stuck into the earth, the light of the sky in the zenith,
which is usually the brightest, will be projected horizontally through
the opening, in whatever direction the person to be communicated with
may be placed. The person who makes the signals must stand on one side
in front of the instrument; and, by passing his hat slowly before the
aperture any number of times, may thus express each unit’s figure of
his signal.

He must then, leaving the light visible, pause whilst he deliberately
counts to himself ten.

He must then with his hat make a number of occultations equal to the
tens figure he wishes to express.

This must be continued for each figure in the number of the signal,
always pausing between each during the time of counting ten.

When the end of the signal is terminated, he must count sixty in the
same manner; and if the signal he gave has not been acknowledged, he
should repeat it until it has been observed.

The same simple telegraph may be used in a dark night, by substituting
a lantern for the looking-glass. The whole apparatus is simple and
cheap, and can be easily carried even by a small boy.

I was led to this contrivance many years ago by reading an account of
a vessel stranded within thirty yards of the shore. {461} Its crew
consisted of thirteen people, ten of whom got into the boat, leaving
the master, who thought himself safer in the ship, with two others of
the crew.

The boat put off from the ship, keeping as much out of the breakers
as it could, and looking out for a favourable place for landing. The
people on shore followed the boat for several miles, urging them not to
attempt landing. But not a single word was audible by the boat’s crew,
who, after rowing several miles, resolved to take advantage of the
first favourable lull. They did so—the boat was knocked to pieces, and
the whole crew were drowned. If the people on the shore could at that
moment have communicated with the boat’s crew, they could have informed
them that, by continuing their course for half a mile further, they
might turn into a cove, and land almost dry.

I was much impressed by the want of easy communication between stranded
vessels and those on shore who might rescue them.


I can even now scarcely believe it credible that the very simple means
I am about to mention has not been adopted years ago. A list of about
a hundred questions, relating to directions and inquiries required to
be communicated between the crew of a stranded ship and those on shore
who wish to aid it, would, I am told, be amply sufficient for such
purposes. Now, if such a list of inquiries were prepared and printed
by competent authority, any system of signals by which a number of
two places of figures can be expressed might be used. This list of
inquiries and answers ought to be printed on cards, and nailed up on
several parts of every vessel. It would be still better, by conference
with other maritime nations, to adopt the same system of signs, and to
have them printed in each language. A looking-glass, a board with a
hole in it, and a {462} lantern would be all the apparatus required.
The lantern might be used for night, and the looking-glass for day

These simple and inexpensive signals might be occasionally found useful
for various social purposes.


Two neighbours in the country whose houses, though reciprocally
visible, are separated by an interval of several miles, might
occasionally telegraph to each other.

If the looking-glass were of large size, its light and its occultation
might be seen perhaps from six to ten miles, and thus become by
daylight a cheap guiding light through channels and into harbours.

It may also become a question whether it might not in some cases save
the expense of buoying certain channels.

For railway signals during daylight it might in some cases be of great
advantage, by saving the erection of very lofty poles carrying dark
frames through which the light of the sky is admitted.

Amongst my early experiments, I made an occulting hand-lantern, with a
shade for occulting by the pressure of the thumb, and with two other
shades of red and of green glass. This might be made available for
military purposes, or for the police.

_Greenwich Time Signals._

It has been thought very desirable that a signal to indicate Greenwich
time should be placed on the Start Point, the last spot which ships
going down the Channel on distant voyages usually sight.

The advantage of such an arrangement arises from this—that chronometers
having had their rates ascertained on shore, may have them somewhat
altered by the motions to {463} which they are submitted at sea. If,
therefore, after a run of above two hundred miles, they can be informed
of the exact Greenwich time, the sea rate of their chronometers will be

Of course no other difficulty than that of expense occurs in
transmitting Greenwich time by electricity to any points on our coast.
The real difficulty is to convey it to the passing vessels. The firing
of a cannon at certain fixed hours has been proposed, but this plan is
encumbered by requiring the knowledge of the distance of the vessel
from the gun, and also from the variation of the velocity of the
transmission of sound under various circumstances.

During the night the flash arising from ignited gunpowder might be
employed. But this, in case of rain or other atmospheric circumstances,
might be impeded. The best plan for night-signals would be to have
an occulting light, which might be that of the lighthouse itself, or
another specially reserved for the purpose.

During the day, and when the sun is shining, the time might be
transmitted by the occultations of reflected solar light, which would
be seen at any distance the curvature of the earth admitted.

The application of my Zenith Light might perhaps fulfil all the
required conditions during daylight.

I have found that, even in the atmosphere of London, an opening only
five inches square can be distinctly seen, and its occultations counted
by the naked eye at the distance of a quarter of a mile. If the side
of the opening were double the former, then the light transmitted to
the eye would be four times as great, and the occultations might be
observed at the distance of one mile.

The looking-glass employed must have its side nearly in {464} the
proportion of three to two, so that one of five feet by seven and a
half ought to be seen at the distance of about eight or nine miles.

_Geological Theory of Isothermal Surfaces._

During one portion of my residence at Naples my attention was
concentrated upon what in my opinion is the most remarkable building
upon the face of the earth, the Temple of Serapis, at Puzzuoli.[63]

[63] In this inquiry I profited by the assistance of Mr.
Head, now the Right Hon. Sir Edmund Head, Bart., K.C.B., late
Governor-General of Canada. An abstract of my own observations
was printed in the “Abstracts of Proceedings” of the Geological
Society, vol. ii. p. 72. My friend’s historical views were printed
in the “Transactions” of the Antiquarian Society.


It was obviously built at or above the level of the Mediterranean in
order to profit by a hot spring which supplied its numerous baths.
There is unmistakable evidence that it has subsided below the present
level of the sea, at least twenty-five feet; that it must have remained
there during many years; that it then rose gradually up, probably to
its former level, and that during the last twenty years it has been
again slowly subsiding.

The results of this survey led me in the following year to explain the
various elevations and depressions of portions of the earth’s surface,
at different periods of time, by a theory which I have called the
theory of the earth’s isothermal surfaces.

I do not think the importance of that theory has been well understood
by geologists, who are not always sufficiently acquainted with physical
science. The late Sir Henry De la Beche perceived at an early period
the great light those sciences might throw upon his own favourite
pursuit, and {465} was himself always anxious to bring them to bear
upon geology.

I am still more confirmed in my opinion of the importance of the
“Theory of Isothermal Surfaces in Geology” from the fact that a few
years afterwards my friend Sir John Herschel arrived independently at
precisely the same theory. I have stated this at length in the notes to
the “Ninth Bridgewater Treatise.”

_Games of Skill._

A considerable time after the translation of Menabrea’s memoir had been
published, and after I had made many drawings of the Analytical Engine
and all its parts, I began to meditate upon the intellectual means
by which I had reached to such advanced and even to such unexpected
results. I reviewed in my mind the various principles which I had
touched upon in my published and unpublished papers, and dwelt with
satisfaction upon the power which I possessed over mechanism through
the aid of the Mechanical Notation. I felt, however, that it would be
more satisfactory to the minds of others, and even in some measure
to my own, that I should try the power of such principles as I had
laid down, by assuming some question of an entirely new kind, and
endeavouring to solve it by the aid of those principles which had so
successfully guided me in other cases.


After much consideration I selected for my test the contrivance of a
machine that should be able to play a game of purely intellectual skill
successfully; such as tit-tat-to, drafts, chess, &c.

I endeavoured to ascertain the opinions of persons in every class of
life and of all ages, whether they thought it required human reason
to play games of skill. The almost constant {466} answer was in the
affirmative. Some supported this view of the case by observing, that
if it were otherwise, then an automaton could play such games. A few
of those who had considerable acquaintance with mathematical science
allowed the possibility of machinery being capable of such work; but
they most stoutly denied the possibility of contriving such machinery
on account of the myriads of combinations which even the simplest games

On the first part of my inquiry I soon arrived at a demonstration that
every game of skill is susceptible of being played by an automaton.

Further consideration showed that if _any position_ of the men upon the
board were assumed (whether that position were possible or impossible),
then if the automaton could make the first move rightly, he must be
able to win the game, always supposing that, under the given position
of the men, that conclusion were possible.

Whatever move the automaton made, another move would be made by his
adversary. Now this altered state of the board is _one_ amongst the
_many positions_ of the men in which, by the previous paragraph, the
automaton was supposed capable of acting.

Hence the question is reduced to that of making the best move under any
possible combinations of positions of the men.

Now the several questions the automaton has to consider are of this

1. Is the position of the men, as placed before him on the board, a
possible position? that is, one which is consistent with the rules of
the game?

2. If so, has Automaton himself already lost the game?

3. If not, then has Automaton won the game? {467}

4. If not, can he win it at the next move? If so, make that move.

5. If not, could his adversary, if he had the move, win the game.

6. If so, Automaton must prevent him if possible.

7. If his adversary cannot win the game at his next move, Automaton
must examine whether he can make such a move that, if he were allowed
to have two moves in succession, he could at the second move have
_two_ different ways of winning the game;

and each of these cases failing, Automaton must look forward to three
or more successive moves.

Now I have already stated that in the Analytical Engine I had devised
mechanical means equivalent to memory, also that I had provided other
means equivalent to foresight, and that the Engine itself could act on
this foresight.


In consequence of this the whole question of making an automaton play
any game depended upon the possibility of the machine being able to
represent all the myriads of combinations relating to it. Allowing one
hundred moves on each side for the longest game at chess, I found that
the combinations involved in the Analytical Engine enormously surpassed
any required, even by the game of chess.


As soon as I had arrived at this conclusion I commenced an examination
of a game called “tit-tat-to,” usually played by little children. It
is the simplest game with which I am acquainted. Each player has five
counters, one set marked with a +, the other set with an 0. The board
consists of a square divided into nine smaller squares, and the object
of each player is to get three of his own men in a straight {468}
line. One man is put on the board by each player alternately. In
practice no board is used, but the children draw upon a bit of paper,
or on their slate, a figure like any of the following.

The successive moves of the two players may be represented as follow:—

1. 2. 3. 4. 5. 6. 7.

│ │ │ │ │ │+ │ │+ +│ │+ +│0│+ +│0│+
─┼─┼─ ─┼─┼─ ─┼─┼─ ─┼─┼─ ─┼─┼─ ─┼─┼─ ─┼─┼─
│ │ │0│ │0│ │0│ │0│ │0│ +│0│
─┼─┼─ ─┼─┼─ ─┼─┼─ ─┼─┼─ ─┼─┼─ ─┼─┼─ ─┼─┼─
│ │ +│ │ +│ │ +│ │0 +│ │0 +│ │0 +│ │0

In this case + wins at the seventh move.

The next step I made was to ascertain what number of combinations were
required for all the possible variety of moves and situations. I found
this to be comparatively insignificant.

I therefore easily sketched out mechanism by which such an automaton
might be guided. Hitherto I had considered only the philosophical
view of the subject, but a new idea now entered my head which seemed
to offer some chance of enabling me to acquire the funds necessary to
complete the Analytical Engine.

It occurred to me that if an automaton were made to play this game,
it might be surrounded with such attractive circumstances that a very
popular and profitable exhibition might be produced. I imagined that
the machine might consist of the figures of two children playing
against each other, accompanied by a lamb and a cock. That the child
who won the game might clap his hands whilst the cock was crowing,
after which, that the child who was beaten might cry and wring his
hands whilst the lamb began bleating.

I then proceeded to sketch various mechanical means by which every
action could be produced. These, when compared with those I had
employed for the Analytical Engine, {469} were remarkably simple. A

Online LibraryCharles BabbagePassages from the Life of a Philosopher → online text (page 33 of 36)