because the relation on which it depends is one which is, so to speak,
exceptional. Still the relation does recur, and with a certain degree
of regularity. When it happens, however, it by no means follows that
we have a very high tide; because it may occur when the tides are near
‘neap’; in other words, when the sun and moon exert opposing effects.
The largest lunar wave cannot stand the drain which the solar wave
exerts upon it at the time of neap tides. Nor would the large lunar
tidal wave produce an exceptionally high tide, even though it were
not the time of ‘neap,’ or were tolerably near the time of ‘spring’
tides. Only when it happens that a large lunar wave combines fully with
the solar wave, do we get very high tides. And when, in addition to
this relation, we have the solar wave nearly at a maximum, we get the
highest of all possible tides. This is what will happen, or all but
happen, on October 5 next. The combination of circumstances is almost
the most effective that can possibly exist.
But, after all, high tides depend very importantly on other
considerations than astronomical ones. Most of us remember how
a predicted high tide some two years ago turned out to be a very
moderate, or, if we may use the expression, a very ‘one-horse’ affair
indeed, because the winds had not been consulted, and exerted their
influence against the astronomers. A long succession of winds blowing
off-shore would reduce a spring tide to a height scarcely exceeding the
ordinary neap. On the other hand, if we should have a long succession
of westerly winds from the Atlantic before the approaching high tide,
it is certain that a large amount of mischief may be done in some of
our riverside regions.[10]
As for the predicted weather changes, they may be regarded as mere
moonshine. A number of predictions, founded on the motions of the sun
and moon, have found a place during many months past in the columns of
a contemporary; but there has been no greater agreement between these
predictions and the weather actually experienced than anyone could
trace between Old Moore’s weather prophecies and recorded weather
changes. In other words, there have been certain accordances which
would be very remarkable indeed if they did not happen to be associated
with as many equally remarkable discordances. Random predictions would
be quite as satisfactory.
A very amusing misprint has found its way into many newspapers in
connection with the coming tide. It is interesting as serving to show
how little is really known by the general public about some of the
simplest scientific matters. The original statement announced that the
sun would not be in perihelion by so many seconds of semi-diameter, in
itself a very incorrect mode of expression. Still it was clear that
what was meant was, that the earth would be so far from the place of
nearest approach to the sun that the latter would not look as large
as it possibly can look, by so many seconds of semi-diameter. In many
papers, however, we read that the ‘sun will not be in perihelion by so
many seconds of mean chronometer!’ Who first devised this marvellous
reading is unknown.
(From the _Daily News_ for September 27, 1869.)
FOOTNOTES:
[10] The wave did little mischief, the winds being easterly.
_DEEP-SEA DREDGINGS._
Men have ever been strangely charmed by the unknown and the seemingly
inaccessible. The astronomer exhibits the influence of this charm as
he constructs larger and larger telescopes, that he may penetrate more
and more deeply beyond the veil which conceals the greater part of the
universe from the unaided eye. The geologist, seeking to piece together
the fragmentary records of the past which the earth’s surface presents
to him, is equally influenced by the charm of mystery and difficulty.
And the microscopist who tries to force from nature the secret of the
infinitely little, is led on by the same strange desire to discover
just those matters which nature has been most careful to conceal from
us.
The energy with which in recent times men have sought to master the
problem of deep-sea sounding and deep-sea dredging is, perhaps, one
of the most striking instances ever afforded of the charm which the
unknown possesses for mankind. Not long ago, one of the most eminent
geographers of the sea spoke regretfully about the small knowledge
men have obtained of the depths of ocean. ‘Greater difficulties,’ he
remarked, ‘than any presented by the problem of deep-sea research
have been overcome in other branches of physical inquiry. Astronomers
have measured the volumes and weighed the masses of the most distant
planets, and increased thereby the stock of human knowledge. Is it
creditable to the age that the depths of the sea should remain in the
category of unsolved problems? that its “ooze and bottom” should be a
sealed volume, rich with ancient and eloquent legends and suggestive of
many an instructive lesson that might be useful and profitable to man?‘
Since that time, however, deep-sea dredging has gradually become more
and more thoroughly understood and mastered. When the telegraphic
cable which had lain so many months at the bottom of the Atlantic was
hauled on board the ‘Great Eastern’ from enormous depths, men were
surprised and almost startled by the narrative. The appearance of the
ooze-covered cable as it was slowly raised towards the surface, and
the strange thrill which ran through those who saw it and remembered
through what mysterious depths it had twice passed; its breaking away
almost from the very hands of those who sought to draw it on board; and
the successful renewal of the attempt to recover the cable,—all these
things were heard of as one listens to a half-incredible tale. Yet when
that work was accomplished deep-sea dredging had already been some time
a science, and many things had been achieved by its professors which
presented, in reality, greater practical difficulties than the recovery
of the Atlantic Cable.
Recently, however, deep-sea researches have been carried on with
results which are even more sensational, so to speak, than the
grappling feat which so surprised us. Seas so deep that many of the
loftiest summits of the Alps might be completely buried beneath them
have been explored. Dredges weighing with their load of mud nearly half
a ton have been hauled up without a hitch from depths of some 14,000
feet. But not merely has comparatively rough work of this sort been
achieved, but by a variety of ingenious contrivances men of science
have been able to measure the temperature of the sea at depths where
the pressure is so enormous as to be equivalent to a weight of more
than 430 tons on every square foot of surface.
The results of these researches are even more remarkable and
surprising, however, than the means by which they have been obtained.
Sir Charles Lyell has fairly spoken of them as so astonishing ‘that
they have to the geologist almost a revolutionary character.’ Let us
consider a few of them.
No light can be supposed to penetrate to the enormous depth just
spoken of. Therefore, how certainly we might conclude that there can
be no life there. If, instead of dealing with the habitability of
planets, Whewell, in his ‘Plurality of Worlds,’ had been considering
the question whether at depths of two or three miles living creatures
could subsist, how convincingly would he have proved the absurdity of
such a supposition. Intense cold, perfect darkness, and a persistent
pressure of two or three tons to the square inch,—such, he might have
argued, are the conditions under which life exists, if at all, in those
dismal depths. And even if he had been disposed to concede the bare
possibility that life of some sort may be found there, then certainly,
he would have urged, some new sense must replace sight—the creatures in
these depths can assuredly have no eyes, or only rudimentary ones.
But the recent deep-sea dredgings have proved that not only does life
exist in the very deepest parts of the Atlantic, but that the beings
which live and move and have their being beneath three miles of water
have eyes which the ablest naturalists pronounce to be perfectly
developed. Light, then, of some sort must exist in those abysms, though
whether the home of the deep-sea animals be phosphorescent, as Sir
Charles Lyell suggests, or whether light reaches these creatures in
some other way, we have no present means of determining.
If there is one theory which geologists have thought more justly
founded than all others, it is the view that the various strata of the
earth were formed at different times. A chalk district, for example,
lying side by side with a sandstone district, has been referred to a
totally different era. Whether the chalk was formed first, or whether
the sandstone existed before the minute races came into being which
formed the cretaceous stratum, might be a question. But no doubt
existed in the minds of geologists that each formation belonged to a
distinct period. Now, however, Dr. Carpenter and Professor Thomson
may fairly say, ‘We have changed all this.’ It has been found that at
points of the sea-bottom only eight or ten miles apart, there may be
in progress the formation of a cretaceous deposit and of a sandstone
region, each with its own proper fauna. ‘Wherever similar conditions
are found upon the dry land of the present day,’ remarks Dr. Carpenter,
‘it has been supposed that the formation of chalk and the formation of
sandstone must have been separated from each other by long periods,
and the discovery that they may actually co-exist upon adjacent
surfaces has done no less than strike at the very root of the customary
assumptions with regard to geological time.’[11]
Even more interesting, perhaps, to many, are the results which have
been obtained respecting the varying temperatures of deep-sea regions.
The peculiarity just considered is, indeed, a consequence of such
variations; but the fact itself is at least as interesting as the
consequences which flow from it. It throws light on the long-standing
controversy respecting the oceanic circulation. It has been found that
the depths of the equatorial and tropical seas are colder than those
of the North Atlantic. In the tropics the deep-sea temperature is
considerably below the freezing-point of fresh water; in the deepest
part of the Bay of Biscay the temperature is several degrees above the
freezing-point. Thus one learns that the greater part of the water
which lies deep below the surface of the equatorial and tropical seas
comes from the Antarctic regions, though undoubtedly there are certain
relatively narrow currents which carry the waters of the Arctic seas
to the tropics. The great point to notice is that the water under
the equatorial seas must really have travelled from polar regions. A
cold of 30 degrees can be explained in no other way. We see at once,
therefore, the explanation of those westerly equatorial currents which
have been so long a subject of contest. Sir John Herschel failed to
prove that they are due to the trade winds, but Maury failed equally to
prove that they are due to the great warmth and consequent buoyancy of
the equatorial waters. In fact, while Maury showed very convincingly
that the great system of oceanic circulation is carried on _despite_
the winds, Herschel proved in an equally convincing manner that the
overflow conceived by Maury should result in an easterly instead of
a westerly current. Recently the theory was put forward that the
continual process of evaporation going on in the equatorial regions
leads to an indraught of cold water in bottom-currents from the polar
seas. Such currents coming _towards_ the equator, that is, travelling
from latitudes where the earth’s eastwardly motion is less to latitudes
where that motion is greater, would lag behind, that is, would have a
westwardly motion. It seems now placed beyond a doubt that this is the
true explanation of the equatorial ocean-currents.
Such are a few, and but a few, among the many interesting results which
have followed from the recent researches of Dr. Carpenter and Professor
Thomson into the hitherto little-known depths of the great sea.
(From the _Spectator_, December 4, 1869.)
FOOTNOTES:
[11] This opinion Dr. Carpenter has since somewhat modified. It will
be remembered, of course, that the evidence derived from the nature of
superposed strata is in no way affected by what is shown above to hold
with adjacent deposits.
_THE TUNNEL THROUGH MONT CENIS._
Men flash their messages across mighty continents and beneath the bosom
of the wide Atlantic; they weigh the distant planets, and analyse
sun and stars; they span Niagara with a railway bridge, and pierce
the Alps with a railway tunnel: yet the poet of the age in which all
these things are done or doing sings, ‘We men are a puny race.’ And
certainly, the great works which belong to man as a race can no more
be held to evidence the importance of the individual man than the vast
coral reefs and atolls of the Pacific can be held to evidence the
working power of the individual coral polype. But if man, standing
alone, is weak, man working according to the law assigned to his race
from the beginning—that is, in fellowship with his kind—is verily a
being of power.
Perhaps no work ever undertaken by man strikes one as more daring than
the attempt to pierce the Alps with a tunnel. Nature seems to have
upreared these mighty barriers as if with the design of showing man how
weak he is in her presence. Even the armies of Hannibal and Napoleon
seemed all but powerless in the face of these vast natural fastnesses.
Compelled to creep slowly and cautiously along the difficult and
narrow ways which alone were open to them, decimated by the chilling
blasts which swept the face of the rugged mountain-range, and dreading
at every moment the pitiless swoop of the avalanche, the French and
Carthaginian troops exhibited little of the pomp and dignity which we
are apt to associate with the operations of warlike armies. Had the
denizen of some other planet been able to watch their progress, he
might indeed have said ‘these men are a puny race.’ In _this_ only,
that _they succeeded_, did the troops of Hannibal and Napoleon assert
the dignity of the human race. Grand as was the aspect of nature, and
mean as was that of man during the progress of the contest, it was
nature that was conquered, man that overcame.
And now man has entered on a new conflict with nature in the gloomy
fastnesses of the Alps. The barrier which he had scaled of old he has
now undertaken to pierce. And the wwww—bold and daring as it seemed—is
three parts finished. (See date of article.)
The Mont Cenis tunnel was sanctioned by the Sardinian Government in
1857, and arrangements were made for fixing the perforating machinery
in the years 1858 and 1859. But the work was not actually commenced
until November 1860. The tunnel—which will be fully seven and a half
miles in length—was to be completed in twenty-five years. The entrance
to the tunnel on the side of France is near the little village of
Fourneau, and lies 3,946 feet above the level of the sea. The entrance
on the side of Italy is in a deep-valley at Bardonèche, and lies 4,380
feet above the sea level. Thus there is a difference of level of 434
feet. But the tunnel will actually rise 445 feet above the level of the
French end, attaining this height at a distance of about four miles
from that extremity; in the remaining three and three-quarter miles
there will be a fall of only ten feet, so that this part of the line
will be practically level.
The rocks through which the excavations have been made have been for
the most part very difficult to work. Those who imagine that the
great mass of our mountain ranges consists of such granite as is made
use of in our buildings, and is uniform in texture and hardness,
greatly underrate the difficulties with which the engineers of this
gigantic work have had to contend. A large part of the rock consists
of a crystallised calcareous schist, much broken and contorted;
and through this rock run in every direction large masses of pure
quartz. It will be conceived how difficult the work has been of
piercing through so diversified a substance as this. The perforating
machines are calculated to work best when the resistance is uniform;
and it has often happened that the unequal resistance offered to the
perforators has resulted in injury to the chisels. But before the work
of perforating began, enormous difficulties had to be contended with.
It will be understood that, in a tunnel of such vast length, it was
absolutely necessary that the perforating processes carried on from
the two ends should be directed with the most perfect accuracy. It has
often happened in short tunnels that a want of perfect coincidence has
existed between the two halves of the work, and the tunnellers from one
end have sometimes altogether failed to meet those from the other. In
a short tunnel this want of coincidence is not very important, because
the two interior ends of the tunnellings cannot in any case be far
removed from each other. But in the case of the Mont Cenis tunnel any
inaccuracy in the direction of the two tunnellings would have been
fatal to the success of the work, since when the two ought to meet
it might be found that they were laterally separated by two or three
hundred yards. Hence it was necessary before the work began to survey
the intermediate country, so as to ascertain with the most perfect
accuracy the bearings of one end of the tunnel from the other. ‘It was
necessary,’ says the narrative of these initial labours, ‘to prepare
accurate plans and sections for the determination of the levels, to
fix the axis of the tunnel, and to “set it out” on the mountain top;
to erect observatories and guiding signals, solid, substantial, and
true.’ When we remember the nature of the passes over the Cenis, we
can conceive the difficulty of setting out a line of this sort over
the Alpine range. The necessity of continually climbing over rocks,
ravines, and precipices in passing from station to station involved
difficulties which, great as they were, were as nothing when compared
with the difficulties resulting from the bitter weather experienced
on those rugged mountain heights. The tempests which sweep the Alpine
passes—the ever-recurring storms of rain, sleet, and driving snow, are
trying to the ordinary traveller. It will be understood, therefore, how
terribly they must have interfered with the delicate processes involved
in surveying. It often happened that for days together no work of any
sort could be done owing to the impossibility of using levels and
theodolites when exposed to the stormy weather and bitter cold of these
lofty passes. At length, however, the work was completed, and that with
such success that the greatest deviation from exactitude was less than
a single foot for the whole length of seven and a half miles.
Equally remarkable and extensive were the labours connected with the
preparatory works. New and solid roads, bridges, canals, magazines,
workshops, forges, furnaces, and machinery had to be constructed;
residences had to be built for the men, and offices for the engineers;
in fact, at each extremity of the tunnel a complete establishment had
to be formed. Those who have traversed Mont Cenis since the works
began have been perplexed by the strange appearance and character of
the machinery and establishments to be seen at Modane and Fourneau. The
mass of pipes and tubes, tanks, reservoirs, and machinery, which would
be marvellous anywhere, has a still stranger look in a wild and rugged
Alpine pass.
(From the _Daily News_, 1869.)
_TORNADOES._
The inhabitants of the earth are subjected to agencies which—beneficial
doubtless in the long run, perhaps necessary to the very existence of
terrestrial races—appear, at first sight, energetically destructive.
Such are—in order of destructiveness—the hurricane, the earthquake,
the volcano, and the thunderstorm. When we read of earthquakes such as
those which overthrew Lisbon, Callao, and Riobamba, and learn that one
hundred thousand persons fell victims in the great Sicilian earthquake
in 1693, and probably three hundred thousand in the two earthquakes
which assailed Antioch in the years 526 and 612, we are disposed to
assign at once to this devastating phenomenon the foremost place
among the agents of destruction. But this judgment must be reversed
when we consider that earthquakes—though so fearfully and suddenly
destructive both to life and property—yet occur but seldom compared
with wind-storms, while the effects of a real hurricane are scarcely
less destructive than those of the sharpest shocks of earthquakes.
After ordinary storms, long miles of the sea-coast are strewn with
the wrecks of many once gallant ships, and with the bodies of their
hapless crews. In the spring of 1866 there might be seen at a single
view from the heights near Plymouth twenty-two shipwrecked vessels, and
this after a storm which, though severe, was but trifling compared with
the hurricanes which sweep over the torrid zones, and thence—scarcely
diminished in force—as far north sometimes as our own latitudes. It
was in such a hurricane that the ‘Royal Charter’ was wrecked, and
hundreds of stout ships with her. In the great hurricane of 1780,
which commenced at Barbadoes and swept across the whole breadth of the
North Atlantic, fifty sails were driven ashore at the Bermudas, two
line-of-battle ships went down at sea, and upwards of twenty thousand
persons lost their lives on the land. So tremendous was the force of
this hurricane (Captain Maury tells us) that ‘the bark was blown from
the trees, and the fruits of the earth destroyed; the very bottom
and depths of the sea were uprooted—forts and castles were washed
away, and their great guns carried in the air like chaff; houses were
razed; ships wrecked; and the bodies of men and beasts lifted up in
the air and dashed to pieces in the storm’—an account, however, which
(though doubtless faithfully rendered by Maury from the authorities he
consulted) must perhaps be accepted _cum grano_, and especially with
reference to the great guns carried in the air ‘like chaff.’[12] (If
so, it ‘blew great guns,’ indeed.)
In the gale of August, 1782, all the trophies of Lord Rodney’s victory,
except the ‘Ardent,’ were destroyed, two British ships-of-the-line
foundered at sea, numbers of merchantmen under Admiral Graves’ convoy
were wrecked, and at sea alone three thousand lives were lost.
But quite recently a storm far more destructive than these swept over
the Bay of Bengal. Most of my readers doubtless remember the great gale
of October 1864, in which all the ships in harbour at Calcutta were
swept from their anchorage, and driven one upon another in inextricable
confusion. Fearful as was the loss of life and property in Calcutta
harbour, the destruction on land was greater. A vast wave swept for
miles over the surrounding country, embankments were destroyed, and
whole villages, with their inhabitants, were swept away. Fifty thousand
souls, it is believed, perished in this fearful hurricane.
The gale which has just ravaged the Gulf of Mexico adds another to
the long list of disastrous hurricanes. As I write, the effects
produced by this tornado are beginning to be made known. Already its
destructiveness has become but too certainly evidenced.
The laws which appear to regulate the generation and the progress of
cyclonic storms are well worthy of careful study.
The regions chiefly infested by hurricanes are the West Indies, the
southern parts of the Indian Ocean, the Bay of Bengal, and the China
Seas. Each region has its special hurricane season.