continents, and of the action of rain upon their interior, and
remembering that unless the process of demolition were checked in some
way, each cause would act from year to year with new force—one through
the effects of the gradual rise of the sea-bed, and the other through
the effects of the gradual increase of the surface of ocean exposed
to the vaporising action of the sun, which increase would necessarily
increase the quantity of rain yearly precipitated on the land—we see
the justice of the opinion expressed by Sir John Herschel, that, ‘had
the primeval world been constructed as it now exists, time enough has
elapsed, and force enough directed to that end has been in activity,
_to have long ago destroyed every vestige of land_.’
We see, then, the necessity that exists for the action of some
restorative or preservative force sufficient to counteract the effects
of the continuous processes of destruction indicated above. If we
consider, we shall see that the destructive forces owe their efficiency
to their levelling action, that is, to their influence in reducing the
solid part of the earth to the figure of a perfect sphere; therefore
the form of force which is required to counteract them is one that
shall tend to produce irregularities in the surface-contour of the
earth. And it will be remarked, that although _upheaval_ is the
process which appears at first sight to be the only effectual remedy
to the levelling action of rains and ocean-currents, yet the forcible
depression of the earth’s surface may prove in many instances yet more
effective, since it may serve to reduce the sea-level in other places.
Now, the earth’s subterranean forces serve to produce the very effects
which are required in order to counteract the continual disintegration
of the shores and interior parts of continents. In the first place,
their action is not distributed with any approach to uniformity over
different parts of the earth’s crust, and therefore the figure they
tend to give to the surface of that crust is not that of a perfect
sphere. This, of itself, secures the uprising of some parts of the
solid earth above the sea-level. But this is not all. On a comparison
of the various effects due to the action of subterranean forces, it
has been found that the forces of upheaval act (on the whole) more
powerfully under continents, and especially under the shore-lines of
continents, while the forces of depression act most powerfully (on the
whole) under the bed of the ocean. It need hardly be said that whenever
the earth is upheaved in one part, it must be depressed somewhere else.
Not necessarily at the same instant, it should be remarked. The process
of upheaval may be either momentarily accompanied by a corresponding
process of depression, or the latter process may take place by a
gradual action of the elastic powers of the earth’s crust; but, in one
way or the other, the balance between upheaval and depression must be
restored. Hence, if it can be shown that for the most part the forces
of upheaval act underneath the land, it follows—though we may not be
able to recognise the fact by obvious visible signs—that processes of
depression are taking place underneath the ocean. Now, active volcanoes
mark the centre of a district of upheaval, and most volcanoes are near
the sea, as if (though, of course, this is not the true explanation)
Nature had provided against the inroads of the ocean by seating the
earth’s upheaving forces just where they are most wanted.
Even in earthquake districts which have no active vent, the same law is
found to prevail. It is supposed by the most eminent seismologists that
earthquake regions around a volcano, and earthquake regions apparently
disconnected from any outlet, differ only in this respect, that in the
one case the subterranean forces have had sufficient power to produce
the phenomena of eruption, while in the other they have not. ‘In
earthquakes,’ says Humboldt, ‘we have evidence of a volcano-producing
force; but such a force, as universally diffused as the internal heat
of the globe, and proclaiming itself everywhere, rarely acts with
sufficient energy to produce actual eruptive phenomena; and when it
does so, it is only in isolated and particular places.’
Of the influence of the earth’s subterranean forces in altering
the level of land, I might quote many remarkable instances, but
considerations of space compel me to confine myself to two or three.
The slow processes of upheaval or depression may, perhaps, seem less
immediately referable to subterranean action than those which are
produced during the progress of an actual earthquake. I pass over,
therefore, such phenomena as the gradual uprising of Sweden, the slow
sinking of Greenland, and (still proceeding westward) the gradual
uprising of Nova Scotia and the shores of Hudson’s Bay. Remarkable
and suggestive as these phenomena really are, and indisputable as the
evidence is on which they rest, they will probably seem much less
striking to the reader than those which I am now about to quote.
On the 19th of November, 1822, a widely felt and destructive earthquake
was experienced in Chili. On the next day, it was noticed for the first
time that a broad line of sea-coast had been deserted by the sea for
more than one hundred miles. A large part of this tract was covered by
shell-fish, which soon died, and exhaled the most offensive effluvia.
Between the old low-water mark and the new one, the fishermen found
burrowing shells, which they had formerly had to search for amidst the
surf. Rocks some way out to sea which had formerly been covered, were
now dry at half ebb-tide.
Careful measurements showed that the rise of the land was greater at
some distance inshore than along the beach. The watercourse of a mill
about a mile inland from the sea had gained a fall of fourteen inches
in little more than a hundred yards. At Valparaiso, the rise was three
feet; at Quintero, four feet.
In February 1835, and in November 1837, a large tract of Chili was
similarly shaken, a permanent rise of two feet following the former
earthquake, and a rise of eight feet the latter.
The earthquake which took place at Cutch in 1819 is perhaps in
some respects yet more remarkable. In this instance, phenomena of
subsidence, as well as phenomena of upheaval, were witnessed. The
estuary of the Indus, which had long been closed to navigation—being,
in fact, only a foot deep at ebb-tide, and never more than six feet at
flood—was deepened in parts to more than eighteen feet at low water.
The fort and village of Sindree were submerged, only the tops of houses
and walls being visible above the water. But although this earthquake
seemed thus to have a land-destroying, instead of a land-creating
effect, yet the instances of upheaval were, even in this case, far more
remarkable than those of depression. ‘Immediately after the shock,’
says Sir Charles Lyell, ‘the inhabitants of Sindree saw at a distance
of five miles and a half from their village a long elevated mound,
where previously there had been a low and perfectly level plain. To
this uplifted tract they gave the name of Ulla-Bund, or the “Mound of
God,” to distinguish it from several artificial dams previously thrown
across the eastern arm of the Indus. It has been ascertained,’ he adds,
‘that this new-raised country is upwards of fifty miles in length from
east to west, running parallel to the line of subsidence which caused
the grounds around Sindree to be flooded. The breadth of the elevation
is conjectured to be in some parts sixteen miles, and its greatest
ascertained height above the original level of the delta is ten feet—an
elevation which appears to the eye to be very uniform throughout.‘
(From _Chambers’s Journal_, November 7, 1868.)
_THE FORCING POWER OF RAIN._
There is an old proverb which implies that England need never fear
drought; and we have had clear evidence this year (1868) that an
exceptionally dry summer is not necessarily followed by a bad harvest.
But I believe that when a balance is carefully struck between the good
and the evil effects resulting from excessive drought in England, it
will be found that the latter largely prevail. In fact, it is only
necessary to observe the effects which have followed the recent wet
weather to recognise the fact that rain has a forcing power, the
very diminished supply of which at the due season cannot fail to
have seriously injurious effects. In various parts of England we see
evidences of the action of such a power during the present autumn in
the blossoming of trees, in the flowering of primroses and other spring
plants, in rich growths of fungi, and in various other ways. It cannot
be doubted that there is here a comparative waste of powers which,
expended in due season, would have produced valuable results.
The modern theories of the correlation of force suffice to show how
enormous a loss a country suffers when there is a failure in the
supply of rain, or when that supply comes out of its due season. When
we consider rain in connection with the causes to which it is due, we
begin to recognise the enormous amount of power of which the ordinary
rainfall of a country is the representative; and we can well understand
how it is that ‘the clouds drop fatness on the earth.’
The sun’s heat is, of course, the main agent—we may almost say the
only agent—in supplying the rainfall of a country. The process of
evaporation carried on over large portions of the ocean’s surface
is continually storing up enormous masses of water in the form of
invisible aqueous vapour, ready to be transformed into cloud, then
wafted for hundreds of miles across seas and continents, to be finally
precipitated over this or that country, according to the conditions
which determine the downfall of rain. These processes do not appear, at
first sight, indicative of any very great expenditure of force, yet in
reality the force-equivalent of the rain-supply of England alone for a
single year is something positively startling. It has been calculated
that the amount of heat required to evaporate a quantity of water which
would cover an area of 100 square miles to a depth of one inch would
be equal to the heat which would be produced by the combustion of half
a million tons of coals. The amount of force of which this consumption
of heat would be the equivalent corresponds to that which would be
required to raise a weight of upwards of one thousand millions of tons
to a height of one mile. Now, when we remember that the area of Great
Britain and Ireland is about 120,000 square miles, and that the annual
rainfall averages about 25 inches, we see that the force-equivalent
of the rainfall is enormous. All the coal which could be raised from
our English coal mines in hundreds of years would not give out heat
enough to produce England’s rain-supply for a single year. When to this
consideration we add the circumstance that the force of rain produces
bad as well as good effects—the former when the rain falls at undue
seasons or in an irregular manner, the latter only when the rainfall
is distributed in the usual manner among the seasons—we see that an
important loss accrues to a country in such exceptional years as the
present.
There are few subjects more interesting than those depending on the
correlation of physical forces; and we may add that there are few the
study of which bears more largely on questions of agricultural and
commercial economy. It is only of late years that the silent forces
of nature—forces continually in action, but which are too apt to pass
unnoticed and unrecognised—have taken their due place in scientific
inquiry. Strangely enough, the subject has been found to have at once
a most practical bearing on business relations, and an aspect more
strikingly poetical than any other subject, perhaps, which men of
science have ever taken in hand to investigate. We see the ordinary
processes of Nature, as they are termed, taking their place in the
workshop of modern wealth, and at the same time exhibited in a hundred
striking and interesting physical relations. What, for instance, can
be stranger or more poetical than the contrast which Professor Tyndall
has instituted between that old friend of the agriculturist—the
wintry snow-flake—and the wild scenery of the Alps? ‘I have seen,’ he
says, ‘the wild stone-avalanches of the Alps, which smoke and thunder
down the declivities with a vehemence almost sufficient to stun the
observer. I have also seen snow-flakes descending so softly as not to
hurt the fragile spangles of which they were composed; yet to produce
from aqueous vapour a quantity which a child could carry of that tender
material demands an exertion of energy competent to gather up the
shattered blocks of the largest stone-avalanche I have ever seen, and
pitch them to twice the height from which they fell.’
I may point out in this place the important connection which exists
between the rainfall of a country and the amount of forest land. I
notice that in parts of America attention is being paid—with markedly
good results—to the influence of forests in encouraging rainfall. We
have here an instance in which cause and effect are interchangeable.
Rain encourages the growth of an abundant vegetation, and abundant
vegetation in turn tends to produce a state of the superincumbent
atmosphere which encourages the precipitation of rain. The consequence
is, that it is very necessary to check, before it is too late, the
processes which lead to the gradual destruction of forests. If these
processes are continued until the climate has become excessively dry,
it is almost impossible to remedy the mischief, simply because the
want of moisture is destructive to the trees which may be planted to
encourage rainfall. Thus there are few processes more difficult (as
has been found by experience in parts of Spain and elsewhere) than
the change of an arid region into a vegetation-covered district. In
fact, if the region is one of great extent, the attempt to effect
such a change is a perfectly hopeless one. On the other hand, the
contrary process—that is, the attempt to change a climate which is too
moist into one of less humidity—is in general not attended with much
difficulty. A judicious system of clearing nearly always leads to the
desired result.
The dryness of the past year has not been due to the want of moisture
in the air, nor to the exceptionally unclouded condition of our
skies. I believe that, on the whole, the skies have been rather more
cloudy than usual this year. The fact that so little dew has fallen
is a sufficient proof that the nights have been on the whole more
cloudy than usual, since, as is well known, the presence of clouds,
by checking the radiation of the earth’s heat, prevents (or at least
diminishes) the formation of dew. The fact would seem to be that the
westerly and south-westerly winds which usually blow over England
during a considerable part of the year, bringing with them large
quantities of aqueous vapour from above the great Gulf Stream, have
this year blown somewhat higher than usual. Why this should be it
is not very easy to say. The height of the vapour-laden winds is
usually supposed to depend on the heat of the weather. In summer, for
instance, the clouds range higher, and therefore travel farther inland
before they fall in rain. In winter, on the contrary, they travel
low, and hence the rain falls more freely in the western than in the
eastern counties during winter. A similar relation prevails in the
Scandinavian peninsula—Norway receiving more rain in winter than in
summer, while Sweden receives more rain in summer than in winter. But
this summer the rain-clouds have blown so much higher than usual as to
pass beyond England altogether. Possibly we may find an explanation
in the fact that before reaching our shores at all the clouds were
relieved by heavy rainfalls—probably due to some exceptional electrical
relations—over parts of the Atlantic Ocean. It is stated that the
steam-ships from America this summer were, in many instances, drenched
by heavy showers until they neared the coasts of England.
(From the _Daily News_, October 5, 1868.)
_A SHOWER OF SNOW-CRYSTALS._
Yesterday morning a remarkably fine fall of snow-stars took place over
many parts of London. The crystals were larger and more perfectly
formed than is commonly the case in our latitudes, where the conditions
requisite for the formation of these beautiful objects are less
perfectly fulfilled than in more northerly regions. Many forms were to
be noticed which the researches of Scoresby, Glaisher, and Lowe have
shown to be somewhat uncommon.
Some of my readers will perhaps be surprised to learn that no less
than 1,000 different kinds of snow-crystals have been noticed by the
observers named above, and that a large proportion of them have been
figured and described. The patterns are of wonderful beauty. A strange
circumstance connected with these objects is the fact that for the most
part they are found, on a close examination, to be formed of minute
coloured crystals—some red, some green, others blue or purple. In fact,
all the colours of the rainbow are to be seen in the delicate tracery
of these fine hexagonal stars. So that in the perfect whiteness of the
driven snow we have an illustration of the well-known fact that the
colours of the rainbow combine to form the purest white. For the common
snow-flake is formed of a large number of such tiny crystals as were
falling yesterday; though their beauty is destroyed in the snow-flake,
through the effects of collision and partial melting. It may not
be very commonly known that ordinary ice, also, is composed of a
combination of crystals presenting all the regularity of formation seen
in the snow-crystals. This would scarcely be believed by anyone who
examined a rough mass of ice taken from the surface of a frozen lake.
Yet, if a slice be cut from the mass and placed in the sun’s light, or
before a fire, the beautiful phenomena called ice-flowers make their
appearance. ‘A fairy seems to have breathed upon the ice, and caused
transparent flowers of exquisite beauty suddenly to blossom in myriads
within it.’
When we remember that the enormous icebergs of the Arctic and Antarctic
seas, the snow-caps which crown the Alps and Andes and Himalayas,
and the glaciers which urge their way with resistless force down the
mountain valleys, are all made up of these delicate and beautiful
snow-flowers, we are struck with the force of the strange contrasts
which Nature presents to our contemplation. We may say of the
snow-crystals what Tennyson said of the small sea-shell. Each snow-star
is
Frail, but a work divine
Made so fairily well,
So exquisitely minute,
A miracle of design.
Yet—massed together with all the prodigality of Nature’s unsparing
hand—they crown the everlasting hills; or, falling in avalanche and
glacier, overwhelm the stoutest works of man; or, in vast islands of
floating ice, show themselves to be
Of force to withstand, year upon year, the shock
Of cataract seas that snap the three-decker’s oaken spine.
(From the _Daily News_, March 11, 1869.)
_LONG SHOTS._
Our artillerists have paid more attention of late years to the
destructive properties of various forms of cannon than to the question
of range. It was different when first the rifling of cannon was under
discussion. Then the subject which was most attentively considered
(after accuracy of fire) was the range which might possibly be
attained by various improvements in the structure of rifled cannon.
Many of my readers will remember how, soon after the construction
of Armstrong guns had been commenced in the Government factories, a
story was spread abroad of the wonderful practice which had been made
with this gun at a range of seven miles. At that tremendous range, a
shot had been fired into the middle of a flock of geese, according
to one version of the story; but this was presently improved upon,
and we were told that a bird had been singled out of the flock by the
artillerists and successfully ‘potted.’ Many believed this little
narrative; though some few, influenced perhaps by the consideration
that a flock of geese would not be visible at a distance of seven
miles, were obstinately incredulous. Presently it turned out that the
Armstrong gun was incapable of throwing a shot to a distance of seven
miles; so that a certain air of improbability has since attached to
the narrative. Still there were not wanting those who referred to
‘Queen Anne’s pocket-pistol’—the cannon which was able to throw shot
across the Straits of Dover; and in the fulness of their faith in that
mythical piece of ordnance, they refused to believe that the skill of
modern artillerists was unequal to the construction of cannon even more
effective.
If there are any who still believe in the powers ascribed to the
far-famed ‘pocket-pistol,’ they will find their confidence in modern
artillery largely shaken by the announcement that it is considered a
great matter that one of Whitworth’s cannon should have thrown a shot
to a distance of very nearly six miles and a half. Not only is this
so, however, but it is well known that no piece of ordnance has ever
flung a projectile to so great a distance since first fire-arms were
invented; and it may be safely predicted that men will never be able
to construct a cannon which—as far as range is concerned—will do much
better than this one of Mr. Whitworth’s. The greatest range which
had ever before been attained fell somewhat short of six miles. The
7-inch steel gun contrived by Mr. Lynall Thomas had flung a projectile
weighing 175 lbs. to a distance of 10,075 yards; and, according to
General Lefroy’s ‘Handbook of Artillery,’ that was the greatest range
ever recorded. But Mr. Whitworth’s cannon has thrown a shot more than
1,000 yards farther.
Very few have any idea of the difficulties which oppose themselves to
the attainment of a great range in artillery practice. It may seem,
at first sight, the simplest possible matter to obtain an increase of
range. Let the gun be made but strong enough to bear a sufficient
charge, and range seems to be merely a question of the quantity of
powder made use of. But in reality the matter is much more complicated.
The artillerist has to contrive that the whole of the powder made use
of shall be burned before the shot leaves the cannon, and yet that the
charge shall not explode so rapidly as to burst the cannon. If he used
some forms of powder, very useful for special purposes, half the charge
would be blown out without doing its share of work. On the other hand,
there are some combustibles (as gun-cotton and the nitrates) which burn
so fast that the gun would be likely to burst before the shot could be
expelled. Then, again, the shot must fit so closely that there shall
be no windage, and yet not so closely as to resist too much the action
of the exploding powder. Again, there is the form of the shot to be
considered. A sphere is not the solid which passes most readily through
a resisting medium like the air; and yet, other projectiles, which are
best so long as they maintain a certain position, meet with a greater
resistance when once they begin to move unsteadily. The conoid used in
ordinary rifle practice, for example, passes much more freely through
the air, point first, than an ordinary spherical bullet; but if the
point did not travel first, as would happen but for the rifling, or
even if the conoidal bullet ‘swayed about’ on its course, it would meet
with more resistance than a spherical bullet. Hence the question of
‘fast or slow rifling’ has to be considered. ‘Fast rifling’ gives the
greater spin, but causes more resistance to the exit of the shot from
the barrel; with ‘slow-rifling,’ these conditions are reversed.