SMALL CONES.
The diminutive cones of Iceland that have exploded
such vast fields of lava, may, like the
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the weight o f water is at each, and the smaller we take these
parts the nearer we shall get to the truth. To take tlie distance
at every foot would be a needless trouble, and for the sake o f convenience
it may be sufficient to take them at intervals o f 32 feet.
The force then required for the first 32 feet that the bottom has to
rise will be represented by 32 x 20 i=:640, which is the number
o f feet that the same force would have raised a weight o f one
atmosphere. For the next 32 feet, it will he 32 x 19 ; for the next,
32 X 18, and so on until it comes to the last 32 feet, which will
he 32 X 2, and the sum of all the terms will represent the number
o f feet through which the same force would have carried a weight
o f one atmosphere.
The two extremes are 643 and 32, the number o f terms 19, and
consequently the sum of them will be—
640 X 64
X 19 6668.
W e shall, however, obtain a nearer approximation if, taking the
intervals the same, we employ the weight suited to the centre o f
that interval as a muliiplier, instead of the weight suited to the
commencement o f it, and the terms of the progression will then be—
3 2 X 1 9 i
3 2 X 184
3 2 X 1 7 i,
and the sum o f 19 terms o f such a progression will be only 6384.
In this calculation a great number o f things are however assumed
that are not strictly true.
1st. It is assumed that the density o f water is no greater at the
depth o f 600 feet than it is at the surface, which is far from being
true.
2nd. It is assumed that the force of gravity is uniform, which
is not the case, strictly speaking. The force o f gravity must be
greater 600 feet below the surface o f the sea, than it is 6000 or
7000 feet above it.
3rd. It is assumed that the weight of the natural atmosphere is
uniform
sunken islands, have once been of much higher
elevation, and broken down by their OAvn weight
into the cavities made by the lava they ejected.
In some parts of the sides of the nearest hills,
or the Laugerfells, were mounds or inequalities
that at a distance bore the resemblance of fine sand
or ashes—indeed, every part of these hills wore a
most rugged and barren aspect, and no description
can possibly convey an adequate idea of the scene
of desolation which here presented itself both on
hill and dale. It was a complete chaos, and glad
were Ave when our horses stepped over the last
rid ere of lava into an even and extensive plain, in
Avhich were descried two lakes, called Laugervalla
and Apa- Vatn, connected by a river winding in a
serpentine course through the plain. Near the
former Ave observed at a short distance three or
four places, out of Avhich Avere issuing A'olumes of
steam or smoke; one in particular, close to the
margin of the lake, had been obser\'ed from a considerable
distance, and appeared more violent in
its ebullitions than the o thers; but anxious to get
uniform during the course of nearly 7000 feet, whereas it is well
known that, in ascending that height above the level of the sea,
the weight o f it is very sensibly diminished.
4th. I t is assumed that the volcano upheaved the crust of
the earth existin g under the sea in one close and compact, and
not as a loose and detached mass, which we know, in the
latter case, could be more easily lifted under water than in the
air.— E . G.
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