Transcribed from the 1844 Matchett, Stevenson, and Matchett edition by
David Price, email ccx074@pglaf.org
[Picture: Public domain book cover]
[Picture: Eccles Church, the present state of the Beach at Happisburgh,
Norfolk. C. Graf. Lith. to Her Majesty. D. Hodgson, delt.]
AN ESSAY
ON THE
ENCROACHMENTS OF THE GERMAN OCEAN
ALONG THE NORFOLK COAST,
WITH
A DESIGN TO ARREST ITS FURTHER DEPREDATIONS;
DEDICATED
TO THE RIGHT HONOURABLE THE
LORDS COMMISSIONERS OF THE ADMIRALTY.
* * * * *
* * * * *
By W. HEWITT, SURGEON.
* * * * *
* * * * *
NORWICH:
PRINTED FOR THE AUTHOR,
BY MATCHETT, STEVENSON, AND MATCHETT, MARKET-PLACE.
SOLD ALSO BY EDWARDS AND HUGHES, 12, AVE-MARIA-LANE, LONDON.
1844.
DEDICATION.
_To the Right Honourable the Lords Commissioners of the Admiralty_.
MY LORDS AND GENTLEMEN,
A communication with your Lordships in 1843, led me to infer that an
Essay upon the interesting subject connected with the present inquiry,
would be received with a degree of attention according to its merits, and
the importance of the object connected with it. But should you, in your
superior wisdom, perceive sufficient evidence has not been advanced to
render it deserving the consideration requisite at your hands, future
proofs may arise upon the foundation contained in the following pages.—On
the contrary, should it meet with your approbation, the high and
honourable position you maintain for the benefit of maritime affairs
will, I trust, induce you to exercise your influence towards effecting a
trial of the plan submitted, for the benefit of the community at large, I
and for the honour and credit of your noble establishment.
I am,
MY LORDS AND GENTLEMEN,
Your very humble and obliged Servant,
THE AUTHOR.
PREFACE.
Many persons may consider it a remarkable circumstance, that an
individual, whose profession requires his leisure time to be devoted to
the acquirement of knowledge for the comfort of man in his corporeal
ailments, should find an opportunity to direct considerable attention to
a subject, so very different in character, as the one now submitted to
the reader. {5} The suggestions, however, of a near, respected, and
venerable relative, aroused and stimulated me to make the strictest
investigation, and subsequently led to the submitting a plan or design
for future benefit, not only to the mariner, the merchant, the
ship-owner, to those whose landed property lies contiguous to the ocean,
but what is of still greater consequence, the preservation of human life;
and although an abler and a more experienced individual might have given
a better statement, or submitted a better design, yet it is hoped
sufficient will be found in this first and hasty attempt, to excite the
attention of the learned and the wealthy.
An acknowledgment of the truth, a grateful feeling for the assistance
derived for the most important particulars on this interesting subject,
induces me to introduce the name, with the exertions of my venerable
relative to the notice of my readers.
The Rev. John Hewitt, B.A., Perpetual Curate of Walcot, in this county,
Vicar of Grantchester, and formerly a Fellow of Corpus Christi College,
Cambridge, after several years of often repeated attention to the subject
embraced in this Essay, expended in the year A.D. 1802 upwards of one
hundred pounds in an attempt to fill up, at his own expence, the worst
breach existing between Waxham and Horsey, and the design to carry it
into effect appeared so feasible, that to lessen the expence, the Hon.
Harbord Harbord, the first Lord Suffield, lent implements to aid the
undertaking. But unfortunately, prior to the task being completed, a
strong north-west wind, upon a spring tide, ensued, and a quantity of
water passed through the breach partially repaired.
A cottager residing near the place, witnessed the circumstance only just
previous to the irruption of the water, and informed my relative had he
possessed a shovel, he could have prevented it.
The circumstance attending this catastrophe caused in little minds
derision and contempt, from the failure of the experiment. But a humble
individual, whose ideas were more enlarged, contended upwards of three
hundred pounds worth of good had been effected; and the spot on that part
of the coast is recognized to this day as Hewitt’s Bank.
While some persons, therefore, considered it a direct failure, my
relative deemed it a partial one, and watched with undiminished ardour
the effect produced by the stranding of the Hunter cutter, A.D. 1807; the
particulars of which are fully entered into in the following pages.
A knowledge of the tides and currents has been principally acquired from
the perusal of several works of the most renowned philosophers, whose
erudition have stamped them with truth stable and incontrovertible. I
have, therefore, adopted their language rather than my own, fearful I
should mar their intent, and my regard for such comprehensive writings
induces me to add the truism transmitted to us by an ancient Latin
author—
Unius ætatis sunt quæ fortiter fiunt, quæ
Vero pro utilitate scribuntur æterna.
_Vegetius_.
Should the design be put in execution, and found efficacious, it will be
applicable to other coasts, by taking every particular respecting them
into consideration, and great will be the reward on the ambition attained
of having endeavoured to benefit the community at large.
THE AUTHOR.
CHAPTER I.
INTRODUCTION.—THE FORMATION OF THE TIDES CONSIDERED, THEIR VARIATION, AND
EFFECTS.
For, lo! the sea that fleets about the land,
And like a girdle clips her solid waste,
Music and measure both doth understand:
For his great crystal eye is always cast
Up to the moon, and on her fixed fast:
And as she danceth in her pallid sphere,
So danceth he about the centre here.
The above lines, so beautifully expressed by one of our earlier poets,
introduces a subject generally understood, but the important object
connected with our present inquiry cannot be maintained without a
thorough knowledge of cause and effect. A minute acquaintance,
therefore, with the formation of the tides and currents, their variation
and effects, transmitted to us by the observations, experiments, and
discoveries of the earlier, and confirmed by the researches of the modern
philosophers, will not be deemed altogether superfluous, as they will
tend to remove any obstacle that might otherwise present itself on the
consideration of so difficult a subject.
By the term tide is meant that regular motion of the sea, according to
which it ebbs and flows twice in the twenty-four hours.
After some wild conjectures of the earliest philosophers, observes
Goldsmith, it became well known in the time of Pliny that the tides were
entirely under the influence in a small degree of the sun, but in a much
greater of the moon. It was found that there was a flux and reflux of
the sea in the space of twelve hours and fifty minutes, which is exactly
the time of a lunar day. It was observed that whenever the moon was in
the meridian, or in other words, as nearly as possible over any part of
the sea, that the sea flowed to that part, and made a tide there; on the
contrary, it was found that when the moon left the meridian, the sea
began to flow back again from whence it came, and there might be said to
ebb. Thus far the waters of the sea seemed very regularly to attend the
motions of the moon. But as it appeared, likewise, that when the moon
was in the opposite meridian, as far off on the other side of the globe,
that there was a tide on this side also, so that the moon produced two
tides, one by her greatest approach to us, and another by her greatest
distance from us; in other words, the moon, in once going round the
earth, produced two tides, always at the same time; one, on the part of
the globe directly under her; and the other, on the part of the globe
directly opposite.
Kepler was the first who conjectured that attraction was the principal
cause; asserting, that the sphere of the moon’s operation extended to the
earth, and drew up its waters. But what Kepler only hinted, has been
completely developed and demonstrated by Sir Isaac Newton.
After his great discovery of the law of gravitation, he found it an easy
matter to account for the whole phenomena of the tides. The moon, like
all the rest of the planets, has been found to attract and to be
attracted by the earth. This attraction prevails throughout our whole
planetary system; the more matter there is contained in any body, the
more it attracts, and its influence decreases in proportion as the
distance, when squared, increases. This being premised, let us see what
must ensue upon supposing the moon in the meridian of any tract of the
sea. The surface of the water immediately under the moon, is nearer the
moon than any part of the globe is, and, therefore, must be more subject
to its attraction than the waters anywhere else. The waters will there
be attracted by the moon, and rise in a heap, whose eminence will be the
highest where the attraction is greatest. In order to form this
eminence, it is obvious that its surface, as well as the depths, will be
agitated, and that wherever the water runs from one part, succeeding
waters must run to fill up the space it has left. Thus the waters of the
sea, running from all parts to attend the motion of the moon, produce the
flowing of the tide; and it is high tide at that part wherever the moon
comes over it, or to its meridian. {11}
But when the moon travels onward, and ceases to point over the place
where the waters were just risen, the cause of their rising ceasing to
operate, they will flow back by their natural gravity into the lower
parts from whence they had travelled; and this retiring of the waters
will form the ebbing of the sea. {12a}
Thus the first part of the demonstration is obvious, since in general it
requires no great sagacity to conceive that the waters nearest the moon
are most attracted or raised highest by the moon. But the other part of
the demonstration, namely, how there come to be high tides at the same
time on the other side of the globe is not so easy to conceive. To
comprehend this, it must be observed, that the part of the earth and its
waters farthest from the moon, are the parts of all others that are least
attracted by the moon; it must also be observed, that all the waters,
when the moon is on the opposite side of the earth, must be attracted in
the same direction that the earth itself attracts them; that is
apparently quite through the body of the earth, towards the moon itself.
This, therefore, being conceived, it is plain that those waters which are
farthest from the moon will have less weight than those of any other part
on the same side of the globe, because the moon’s attraction, which
conspires with the earth’s attraction, is there least. Now, therefore,
the waters farthest from the moon having less weight, and being lightest,
will be pressed on all sides by those that having more attraction are
heavier, and the heavier waters flowing in, will make them swell and rise
in an eminence directly opposite to that on the other side of the globe,
caused by the more immediate influence of the moon. {12b}
In this manner the moon, in one diurnal revolution, produces two tides;
one raised immediately under the sphere of its influence, and the other
directly opposite to it. As the moon travels, this vast body of waters
rears upward, as if to watch its motions, and pursues the same constant
rotation. However, in this great work of raising the tides, the sun has
no small share, it produces its own tide constantly every day, just as
the moon does, but in a much less degree, because the sun is at an
immensely greater distance. Thus there are solar tides and lunar
tides—when the forces of these two great luminaries concur, which they
always do when they are either in the same or in the opposite parts of
the heavens, they jointly produce a much greater tide, than when they are
so situated in the heavens as each to make peculiar tides of their own;
in the former, the attraction of the sun conspires with the attraction of
the moon, by which means the high spring tides are formed; in the latter,
the action of the sun is opposed to that of the moon, consequently the
effect must be to depress the waters where the moon’s action has a
tendency to raise them, and hence the production of the lower neap tides.
{13a}
The spring tides {13b} do not take place on the very day of the new and
full moon, nor the neap tides on the very day of the quadratures, but a
day or two after; the effect is neither greatest nor least when the
immediate influence of the cause is greatest or least: as the greatest
heat, for example, is not on the solstitial day, when the immediate
action of the sun is greatest, but some time after it.—And although the
action of the sun and moon were to cease, yet the ocean would continue to
ebb and flow for some time, as its waves continue in violent motion for
some time after a storm. {14a}
Sir Isaac Newton has shown that the tides increase as the cube of the
distances decrease, so that the moon, at half her present distance, would
produce a tide eight times greater. Now the moon describes an ellipse
about the earth, and of course must be once in every revolution nearer
the earth than in any other part of her orbit; consequently she must
produce a much higher tide when in this point of her orbit than in the
opposite point. {14b}
This is the reason that two great spring tides never take place
immediately after each other; for if the moon be at her least distance at
the time of new moon, she must be at her greatest distance at the time of
full moon, having performed half a revolution in the intervening time;
and, therefore, the spring tide at the full will be much less than at the
preceding change. For the same reason, if a great spring tide happens at
the time of full moon, the tide at the following change will be less.
{14c}
The spring tides are highest and the neap tides lowest about the
beginning of the year; for the earth being nearest the sun about the
first of January, must be more strongly attracted by that body than at
any other time of the year: hence the spring tides which happen about
that time, will be greater than at any other time, and should the moon be
new or full in that part of her orbit, which is nearest to the earth at
the same time, the tides will be considerably higher than at any other
time of the year.
The tide which happens at any time while the moon is above the horizon,
is called the superior tide, and when below the horizon, the inferior.
When the moon is in the equinoctial, the superior and inferior tides are
of the same height, but when the moon declines towards the elevated pole,
the superior tide is higher than the inferior. If the latitude of the
place and the declination of the moon are of contrary names, the inferior
tides will be the highest. But the highest tide at any particular place
is when the moon’s declination is equal to the latitude of the place, and
of the same name, and the height of the tide diminishes as the
differences between the latitude and declination increases, therefore the
nearer any place is to that parallel whose latitude is equal to the
moon’s declination and of the same name, the higher will be the tide at
that place. In comparing the height of tides at different places, it is
supposed that the sun and moon are at the same distances from the earth,
and in the same position with respect to the meridian of these places.
{15a}
The above observations relative to the regularity of the tides could only
result by supposing the earth to be covered with the waters of the ocean
to a great depth, but as this is not the case, it is only at places
situated on the shores of large oceans where such tides exist. {15b}
From local circumstances the tides are subject to great irregularities,
such as meeting with islands, headlands, passing through straits, &c. In
order that they may have their full motion, the ocean in which they are
produced ought to extend 90° from east to west, because that is the
distance between the greatest elevation and the greatest depression
produced in the waters by the moon.
Hence it is that the tides in the Pacific Ocean exceed those of the
Atlantic, and that they are less in that part of the Atlantic which is
within the torrid zone between Africa and America, than on the temperate
zones on either side of it where the ocean is much broader. {16a}
Tides are not perceptible in lakes and most inland seas, and deep and
extensive as is the Mediterranean, are scarcely sensible to ordinary
observation, their effects being quite subordinate to the winds and
currents. In some places, however, as in the Straits of Messina, there
is an ebb and flow to the amount of two feet and upwards; at Naples and
at the Euripus, of twelve and thirteen inches, and Rennell informs us, at
Venice, of five feet. {16b}
The ebb and flow of the ocean is very slight in islands remote from any
continent, as for example, at St. Helena, where it seldom exceeds three
feet. Tides are remarkably high on the coasts of Malay, in the Straits
of Sunda, on the open coast of Patagonia, along the coasts of China and
Japan, at Panama, in the Gulph of Bengal, and at the mouth of the Indus,
where the water rises thirty feet in height. Tides are greatest in any
given line of coast, in narrow bays and estuaries; and are least in the
intervening tracts where the land is prominent. {16c}
On the authority of the late Captain Hewett, R.N., at the entrance of the
estuary of the Thames, the rise of the spring tides is eighteen feet; but
when we follow our eastern coast from thence northward; towards Lowestoft
and Yarmouth, we find a gradual diminution, until at the place last
mentioned the highest rise is only seven or eight feet. From this point
there begins again to be an increase, so that at Cromer, where the coast
again retires towards the west, the rise is sixteen feet; and towards the
extremity of the gulph called “the Wash,” as at Lynn and in Boston Deeps,
it is from twenty-two to twenty-four, and in some extraordinary cases,
twenty-six feet. From thence again there is a decrease towards the
north; the elevation at the Spurn Point being from nineteen to twenty
feet, and at Flamborough Head, on the Yorkshire coast, from fourteen to
sixteen feet.
It is also recorded, on the authority of Captain Beaufort, R.N., that at
Milford Haven, in Pembrokeshire, at the mouth of the Bristol Channel, the
tides rise thirty-six feet, and at King-road, near Bristol, forty-two
feet. At Chepstow, on the Wye, a small river which opens into the
estuary of the Severn, they reach fifty feet, sometimes sixty-nine, and
even seventy-two feet. {17}
The tides at Tonquin are the most remarkable in the world. In this part
there is but one tide and one ebb every twenty-four hours; whereas in
other places there are two. Besides twice in each month there is no tide
at all, when the moon is near the equinoctial, the water being for some
time quite stagnant. These, with other peculiar appearances attending
the same phenomena, were considered by many as inscrutable; but Sir Isaac
Newton adjudged them to arise from the concurrence of two tides, one from
the South Sea, and the other from the Indian Ocean. Of each of these
tides there come successively two every day; two at one time greater, and
two at another that are less. The time between the arrival of the two
greater is considered by him as high tide; the time between the two
lesser as ebb. In short, with this clue that great mathematician solved
every appearance, and so established his theory as to silence every
opposer. This fluctuation of the sea from the tides, observes the same
author, produces another and more constant rotation of its waters from
the east to the west, in this respect following the course of the moon.
This may be considered as one great and general current of the waters of
the sea; and although it be not every where distinguishable, it is
nevertheless every where existent, except when opposed by some particular
current or eddy produced by partial and local causes. This tendency of
the sea towards the west is plainly perceivable in all the great straits
of the ocean; as for instance, in those of Magellan, in South America,
where the tide running in from the east nearly twenty feet high, and
continues flowing six hours, whereas the ebb continues but two hours, and
the current is directed to the west. This proves that the flux is not
equal to the reflux, and that from both results a motion of the sea
westward, which is more powerful during the time of the flux than the
reflux. This motion westward has been sensibly observed by navigators in
their passage back from India to Madagascar, and so on to Africa. In the
great Pacific, also, it is very perceivable; but the places where it is
most obvious are, as it was said, in those straits which join one ocean
to another. In the straits between the Maldivia Islands, in the gulph of
Mexico, between Cuba and Jucatan. In the straits in the gulph of Paria,
the motion is so violent, that it has received the appellation of the
Dragon’s Mouth. Northward, in the sea of Canada, in Waigat’s straits, in
the straits of Java, and in short, where the ocean on one part pours into
the ocean on the other. In this manner is the sea carried with an
unceasing circulation round the globe, and at the same time that its
waters are pushed backward and forward with the tide; they have thus a
progressive current to the west, which, though less observable, is not
the less real. {19}