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those writers who have referred to it has, as far as my information
goes, been unanimous.

{441}




CHAPTER XXXIV.

THE AUTHOR’S FURTHER CONTRIBUTIONS TO HUMAN KNOWLEDGE.


Glaciers — Uniform Postage — Weight of the Bristol Bags — Parcel
Post — Plan for transmitting Letters along Aërial Wires — Cost
of Verification is part of Price — Sir Rowland Hill — Submarine
Navigation — Difference Engine — Analytical Engine — Cause of Magnetic
and Electric Rotations — Mechanical Notation — Occulting Lights —
Semi-occultation may determine Distances — Distinction of Lighthouses
numerically — Application from the United States — Proposed Voyage —
Loss of the Ship and Mr. Reid — Congress of Naval Officers at Brussels
in 1853 — My Portable Occulting Light exhibited — Night Signals —
Sun Signals — Solar Occulting Lights — Afterwards used at Sebastopol
— Numerical Signals applicable to all Dictionaries — Zenith Light
Signals — Telegraph for Ships on Shore — Greenwich Time Signals —
Theory of Isothermal Surfaces to account for the Geological Facts of
the successive Uprising and Depression of various parts of the Earth’s
Surface — Games of Skill — Tit-tat-to — Exhibitions — Problem of the
Three Magnetic Bodies.


_Of Glaciers._

Much has been written upon the subject of glaciers. The view which I
took of the question on my first acquaintance with them still seems to
me to afford a sufficient explanation of the phenomena. It is probable
that I may have been anticipated in it by Saussure and others; but,
having no time to inquire into its history, I shall give a very brief
statement of those views.

The greater part of the material which ultimately constitutes a glacier
arises from the rain falling and the snow deposited in the higher
portions of mountain ranges, which {442} naturally first fill up the
ravines and valleys, and rests on the tops of the mountains, covering
them to various depths.

The chief facts to be explained are—first, the causes of the descent
of these glaciers into the plains; second, the causes of the
transformation of the opaque consolidated snow at the sources of the
glacier into pure transparent ice at its termination.

The glaciers usually lying in valleys having a steep descent,
gravity must obviously have a powerful influence; but its action is
considerably increased by another cause.

The heat of the earth and that derived from the friction of the glacier
and its broken fragments against the rock on which it rests, as well as
from the friction of its own fragments, slowly melts the ice, and thus
diminishing the amount of its support, the ice above cracks and falls
down upon the earth, again to be melted and again to be broken.

But as the ice is upon an inclined plane, the pressure from above,
on the upper side of the fragment, will be greater than that on the
lower; consequently, at every fall the fallen mass will descend by a
very small quantity further into the valley. Another consequence of the
melting of the lower part of the centre of the glacier will be that the
centre will advance faster than the sides, and its termination will
form a curve convex towards the valley.

The above was, I believe, the common explanation of the formation of
glaciers. The following part explains my own views:—


_Of the Causes of the Transformation of Condensed Snow into Transparent
Ice._

It is a well-known fact that water rapidly frozen retains all the air
it held in solution, and is opaque. {443}

It is also known that water freezing very slowly is transparent.

Whenever, by the melting of the lower portion of any part of a glacier,
a piece of it cracks and falls to a lower level, the friction of the
broken sides will produce heat, and melt a small portion of water.
This water, trickling down very slowly, will form a thin layer on the
broken surface, and a portion will be retained in the narrowest part
of the crack. But, since the temperature of a glacier is very near the
freezing point, that water will freeze very slowly. It will, therefore,
become transparent ice, and will, as it were, solder together the two
adjacent surfaces by a thin layer of transparent ice.

But the transparent ice is much stronger and more difficult to break
than opaque ice; consequently, the next time the soldered fragments are
again broken, they will not break in the strongest part, which is the
transparent ice: but the next fracture will occur in the opaque ice, as
it was at first.

Thus, by the continued breaking and falling downward of the fragments
of the glacier, as it proceeds down the valley, a series of vertical,
rudely-parallel veins of transparent ice will be formed. As these
masses descend the valley, fresh vertical layers of transparent ice
will be interposed between those already existing until the whole takes
that beautiful transparent cerulean tint which we so frequently see at
the lower termination of a glacier. Another effect of this vertical
fracture at the surfaces of least resistance will be alternate vertical
layers of opaque and transparent ice shading into each other. This
would, in some of its stages, give a kind of ribboned appearance to the
ice. Probably traces of it would still be exhibited even in the most
transparent ice. Speaking roughly, this ribboned structure ought to
be closer together the nearer the piece examined is to the end of the
glacier. It {444} ought also to be more apparent towards the centre
of the glacier than towards the sides. The effect of this progress
downward is to produce a very powerful friction between the masses of
ice and the earth over which they are pushed, and, consequently, a
continual accession to that stream of water which is found issuing from
all glaciers.

The result of this continual breaking up is to cause all the water
melted by the friction of the blocks of ice which is not retained in
the interstices to fall towards the lowest part of the descending
valley, and thus increase the stream, and so take away more and more of
the support of the central part of the glacier. Hence the advance of
the surface of the glacier will be much quicker towards its middle than
near the sides.

〈CRACKS IN GLACIERS PERPENDICULAR.〉

The consequence of these actions is, that cracks in the ice will occur
generally in planes perpendicular to its surface. The rain which falls
upon the glacier, the water produced from its surface by the sun’s rays
and by the effect of the temperature of the atmosphere, as well as
the water produced by the friction of its descending fragments, will
penetrate through these cracks, and be retained by capillary action
on the surfaces, and still more where the distance of the adjacent
surfaces is very small. The rest of this unfrozen water will reach the
rocky bottom of the glacier, and give up some of its heat to the bed
over which it passes, to be again employed in melting away the lowest
support of the glacier ice. Although the temperature of the glacier
should differ but by a very small quantity from that of the freezing
point of water, yet these films will only freeze the more slowly, and
therefore become more solid and transparent ice. Their very thinness
will enable all the air to be more readily extricated by freezing.

The question of the _regelation_ of pounded ice, if by that {445} term
is meant anything more than welding ice by heat, or of joining its
parts by a process analogous to that which is called _burning together_
two separate portions of a bronze statue, has always appeared to me
unsatisfactory.

〈BURNING TOGETHER BRONZE.〉

The process of “burning together” is as follows:—Two portions of a
large statue, which have been cast separately, are placed in a trough
of sand, with their corresponding ends near to each other. A channel
is made in the sand, leading through the junction of the parts to be
united.

A stream of melted bronze is now allowed to run out from the furnace
through the channel between the contiguous ends which it is proposed
to unite. The first effect of this is to heat the ends of the two
fragments. After the stream of melted metal has continued sometime, the
ends of those fragments themselves begin to melt. When a small quantity
of each end is completely melted, the further flow of the melted metal
is stopped, and as soon as the pool of melted metal connects, the two
ends of the pieces to be united begins to consolidate: the whole is
covered up with sand and allowed to cool gradually. When cold, the
unnecessary metal is cut away, and the fragments are as perfectly
united as if they had been originally cast in one piece.

The sudden consolidation, by physical force, of pounded ice or snow
appears to me to arise from the first effect of the pressure producing
heat, which melts a small portion into water, and brings the particles
of ice or snow nearer to each other. The portion of water thus produced
then, having its heat abstracted by the ice, connects the particles of
the latter more firmly together by freezing.

If two flat surfaces of clear ice had a heated plate of metal put
between them, two very thin layers of water would be formed between
the ice and the heated plate. If the hot {446} plate were suddenly
withdrawn, and the two plates of ice pressed together, they would then
be frozen together. This would be equivalent to welding. In all these
cases the temperature of the ice must be a very little lower than the
freezing-point. The more nearly it approached that point the slower the
process of freezing would be, and therefore the more transparent the
ice thus formed.

〈ICE FROZEN IN THE EXHIBITION, 1862.〉

In the Exhibition of 1862 there were two different processes by which
ice was produced in abundance, even in the heat of the Machinery Annex,
in which they were placed.

In both the water was quickly converted into ice, and in both cases the
ice was opaque.

In one of them the ice was produced in the shape of long hollow
cylinders. These were quite opaque, and were piled up in stacks. The
temperature of the place caused the ice to melt slowly; consequently,
the interstices where the cylinders rested upon each other, received
and retained a small portion of the water, which, trickling down, was
detained by capillary attraction. Here it was very slowly frozen, and
formed at the junction of the cylinders a thin film of transparent ice.
This gradually increased as the upper cylinders of the ice melted away,
and, after several hours’ exposure, I have seen clear transparent ice
a quarter of an inch thick, where, at the commencement, there had not
been even a trace of translucency.

On inquiring of the operator why the original cylinders were opaque,
he told me, because they were frozen quickly. I then pointed out to
him the small portions of transparent ice, which I have described, and
asked him the cause. He immediately said, because they had been frozen
slowly.

It appeared to be an axiom, derived from his own experience, that water
quickly frozen is always opaque, and water {447} slowly frozen always
transparent. I pointed out this practical illustration to many of the
friends I accompanied in their examination of the machinery of the
Annex.

It would follow from this explanation, that glaciers on lofty mountains
and in high latitudes may, by their own action, keep the surface of
the earth on which they rest at a higher temperature than it would
otherwise attain.


_Book and Parcel Post._

When my friend, the late General Colby, was preparing the materials
and instruments for the intended Irish survey, he generally visited
me about once a week to discuss and talk over with me his various
plans. We had both of us turned our attention to the Post-office, and
had both considered and advocated the question of a uniform rate of
postage. The ground of that opinion was, that the actual _transport_ of
a letter formed but a small item in the expense of transmitting it to
its destination; whilst the heaviest part of the cost arose from the
_collection_ and _distribution_, and was, therefore, almost independent
of the length of its journey. I got some returns of the weight of
the Bristol mail-bag for each night during one week, with a view to
ascertain the possibility of a more rapid transmission. General Colby
arrived at the conclusion that, supposing every letter paid sixpence,
and that the same number of letters were posted, then the revenue
would remain the same. I believe, when an official comparison was
subsequently made, it was found that the equivalent sum was fivepence
halfpenny. I then devised means for transmitting letters enclosed in
small cylinders, along wires suspended from posts, and from towers, or
from church steeples. I made a little model of such an apparatus, and
thus transmitted notes from my front drawing-room, through the house,
{448} into my workshop, which was in a room above my stables. The date
of these experiments I do not exactly recollect, but it was certainly
earlier than 1827.

〈COST OF VERIFICATION.〉

I had also, at a still earlier period, arrived at the remarkable
economical principle, _that one element in the price of every article
is the cost of its verification_. It arose thus:—

In 1815 I became possessed of a house in London, and commenced my
residence in Devonshire Street, Portland Place, in which I resided
until 1827. A kind relative of mine sent up a constant supply of
game. But although the game cost nothing, the expense charged for its
carriage was so great that it really was more expensive than butchers’
meat. I endeavoured to get redress for the constant overcharges, but
as the game was transferred from one coach to another I found it
practically impossible to discover where the overcharge arose, and thus
to remedy the evil. These efforts, however, led me to the fact that
_verification_, which in this instance constituted a considerable part
of the _price of the article, must form a portion of its price in every
case_.

Acting upon this, I suggested that if the Government were to become,
through the means of the Post-office, parcel carriers, they would
derive a greater profit from it than any private trader, because the
whole price of verification would be saved by the public. I therefore
recommended the enlargement of the duties of the Post-office by
employing it for the conveyance of books and parcels.

I mention these facts with no wish to disparage the _subsequent_
exertions of Sir Rowland Hill. His devotion to the subject, his
unwearied industry, and his long and at last successful efforts to
overcome the notorious official friction of that department, required
all the enduring energy he so constantly bestowed upon the subject.
The benefit {449} conferred upon the country by the improvements he
introduced is as yet scarcely sufficiently estimated.

These principles were published afterwards in the “Economy of
Manufactures.”—See First Edition, 8th June, 1832; Second Edition, 22nd
November, 1832. See chap. on the “Influence of Verification on Price,”
p. 134, and “Conveyance of Letters,” p. 273.


_Submarine Navigation._

Of this it is not necessary to do more than mention the title and refer
for the detail to the chapter on Experience by Water: and also to the
article Diving Bell in the “Encyclopædia Metropolitana.”

I have only to add my opinion that in open inverted vessels it may
probably be found, under certain circumstances, of important use.


_Difference Engine._

Enough has already been said about that unfortunate discovery in
the previous part of this volume. The first and great cause of its
discontinuance was the inordinately extravagant demands of the
person whom I had employed to construct it for the Government. Even
this might, perhaps, by great exertions and sacrifices, have been
surmounted. There is, however, a limit beyond which human endurance
cannot go. If I survive some few years longer, the Analytical Engine
will exist, and its works will afterwards be spread over the world.
If it is the will of that Being, who gave me the endowments which led
to that discovery, that I should not survive to complete my work, I
bow to that decision with intense gratitude for those gifts: conscious
that through life I have never hesitated to make the {450} severest
sacrifices of fortune, and even of feelings, in order to accomplish my
imagined mission.

The great principles on which the Analytical Engine rests have been
examined, admitted, recorded, and demonstrated. The mechanism itself
has now been reduced to unexpected simplicity. Half a century may
probably elapse before any one without those aids which I leave behind
me, will attempt so unpromising a task. If, unwarned by my example,
any man shall undertake and shall succeed in really constructing an
engine embodying in itself the whole of the executive department
of mathematical analysis upon different principles or by simpler
mechanical means, I have no fear of leaving my reputation in his
charge, for he alone will be fully able to appreciate the nature of my
efforts and the value of their results.


_Explanation of the Cause of Magnetic and Electric Rotations._

In 1824 Arago published his experiments on the magnetism manifested
by various substances during rotation. I was much struck with the
announcement, and immediately set up some apparatus in my own workshop
in order to witness the facts thus announced.

My friend Herschel, who assisted at some of the earliest experiments,
joined with me in repeating and varying those of Arago. The results
were given in a joint paper on that subject, published in the
“Transactions of the Royal Society” in 1825.

I had previously made some magnetic experiments on a large magnet
which would, under peculiar management, sustain about 32½ lbs. It was
necessary to commence with a weight of about 28 lbs., and then to add
at successive intervals additional weights, but each less and less than
the former. {451}

〈ON ELECTRIC ROTATIONS.〉

This led me to an explanation of the cause of those rotations, which
I still venture to think is the true cause, although it is not so
recognized by English philosophers.

The history is a curious one, and whether the cause which I assigned
is right or wrong, the train of thought by which I was led to it is
valuable as an illustration of the mode in which the human mind works
in its progress towards new discoveries.

The first experiment, showing that the weight suspended might be
increased at successive intervals of time, was stated in most treatises
on magnetism. But the visible fact impressed strongly on my mind the
conclusion that the production and discharge of magnetism is not
instantaneous, but requires time for its complete action. It appeared,
therefore, to me that this principle was sufficient for the explanation
of the rotations observed by Arago.

In the following year it occurred to me that electricity possessed the
same property, namely, that of requiring time for its communication.
I then instituted a new series of experiments, and succeeded, as I
had anticipated, in producing electric rotations. But a new fact now
presented itself: in certain cases the electric needle moved back in
the contrary direction to that indicated by the influences to which
it was subjected. Whenever this occurred the retrograde motion was
always very slow. After eliminating successively by experiment every
cause which I could imagine, the fact which remained was, that in
certain cases there occurred a motion in the direction opposite to
that which was expected. But whenever such a motion occurred it was
always very slow. Upon further reflection, I conjectured that it might
arise from the screen, interposed between the electric and the needle
itself, becoming electrified possibly in the opposite direction. New
experiments confirmed this view and proved {452} that the original
cause was sufficient for the production of all the observed effects.

These experiments and their explanation were printed in the “Phil.
Trans.” 1826. But they met with so little acceptance in England that I
had ceased to contend for them against more popular doctrines, and was
too deeply occupied with other inquiries to enter on their defence.
Several years after, during a visit to Berlin, taking a morning walk
with Mitscherlich, I asked what explanation he adopted of the magnetic
rotations of Arago. He instantly replied, “There can be no doubt that
yours is the true one.”

It will be a curious circumstance in the history of science, if an
erroneous explanation of new and singular experiments in one department
should have led to the prevision of another similar set of facts in a
different department, and even to the explanation of new facts at first
apparently contradicting it.


_Mechanical Notation._

This also has been described in a former chapter. I look upon it as one
of the most important additions I have made to human knowledge. It has
placed the construction of machinery in the rank of a demonstrative
science. The day will arrive when no school of mechanical drawing will
be thought complete without teaching it.


_Occulting Lights._

The great object of all my inquiries has ever been to endeavour to
ascertain those laws of thought by which man makes discoveries. It was
by following out one of the principles which I had arrived at that I
was led to the system of occulting numerical lights for distinguishing
lighthouses {453} and for night signals at sea, which I published
about twelve years ago. The principle I allude to is this:—

〈PRINCIPLE OF INVENTION.〉

Whenever we meet with any defect in the means we are contriving for the
accomplishing a given object, that defect should be noted and reserved
for future consideration, and inquiry should be made—

_Whether that which is a defect as regards the object in view may not
become a source of advantage in some totally different subject._

I had for a long series of years been watching the progress of
electric, magnetic, and other lights of that order, with the view of
using them for domestic purposes; but their want of uniformity seemed
to render them hopeless for that object. Returning from a brilliant
exhibition of voltaic light, I thought of applying the above rule. The
accidental interruptions might, by breaking the circuit, be made to
recur at any required intervals. This remark suggested their adaptation
to a system of signals. But it was immediately followed by another,
namely: that the interruptions were equally applicable to all lights,
and might be effected by simple mechanism.

〈UNEXPECTED DIFFICULTY.〉

I then, by means of a small piece of clock-work and an argand lamp,
made a _numerical_ system of occultation, by which any number might be
transmitted to all those within sight of the source of light. Having
placed this in a window of my house, I walked down the street to the
distance of about 250 yards. On turning round I perceived the number
32 clearly indicated by its occultations. There was, however, a small
defect in the apparatus. After each occultation there was a kind of
semi-occultation. This arose from the arm which carried the shade
rebounding from the stop on which it fell. Aware that this defect could
be easily remedied, I {454} continued my onward course for about 250
yards more, with my back towards the light. On turning round I was much
surprised to observe that the signal 32 was repeated distinctly without
the slightest trace of any semi-occultation or blink.

I was very much astonished at this change; and on returning towards
my house had the light constantly in view. After advancing a short
distance I thought I perceived a very faint trace of the blink. At
thirty or forty paces nearer it was clearly visible, and at the
half-way point it was again perfectly distinct. I knew that the remedy
was easy, but I was puzzled as to the cause.

After a little reflection I concluded that it arose from the
circumstance that the small hole through which the light passed was
just large enough to be visible at five hundred yards, yet that when
the same hole was partially covered by the rebound there did not remain
sufficient light to be seen at the full distance of five hundred yards.

Thus prepared, I again applied the principle I had commenced with and
proceeded to examine whether this defect might not be converted into an



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