Copyright
D. S. (David Samuel) Margoliouth.

The Popular science monthly (Volume 19) online

. (page 6 of 110)
Online LibraryD. S. (David Samuel) MargoliouthThe Popular science monthly (Volume 19) → online text (page 6 of 110)
Font size
QR-code for this ebook


cording to our ideas from an insect's point of view ! The air
infested with huge flying hungry dragons, whose gaping and snapping
mouths are ever intent upon swallowing the innocent creatures for
whom, according to the insect, if he were like us, a properly con-
structed Avorld ought to be exclusively adapted. The solid earth con-
tinually shaken by the approaching tread of hideous giants — moving
mountains — that crush out precious lives at every footstep, an occa-
sional draught of the blood of these monsters, stolen at life-risk, afford-
ing but poor compensation for such fatal persecution.

Let us hope that the little victims are less like ourselves than the
doings of ants and bees might lead us to suppose ; that their mental
anxieties are not proportionate to the optical vigilance indicated by
the four thousand eye-lenses of the common house-fly, the seventeen
thousand of the cabbage-butterfly and the wide-awake dragon-fly, or
the twenty-five thousand possessed by certain species of still more
vigilant beetles.

Each of these little eyes has its own cornea, its lens, and a curious
six-sided, transparent prism, at the back of which is a special retina
spreading out from a branch of the main ojitic nen'e, which, in the
cockchafer and some other creatures, is half as large as the brain. If
each of these lenses forms a separate picture of each object rather than
a single mosaic picture, as some anatomists suppose, what an awful
army of cruel giants must the cockchafer behold when he is captured
by a schoolboy !

The insect must see a whole world of wonders of which we know
little or nothing. True, we have microscopes, with which we can see
one thing at a time if carefully laid upon the stage ; but what is the
finest instrument that Ross can produce compared to that with twenty-
five thousand object-glasses, all of them probably achromatic, and
each one a living instrument with its own nerve-branch supplying a
separate sensation ? To creatures thus endowed with microscopic vi-
sion, a cloud of sandy dust must appear like an avalanche of massive
rock-fragments, and everything else proportionally monstrous.

One of the many delusions engendered by our human self-conceit
iiid habit of considering the world as onlv such as we know it from



44 THE POPULAR SCIENCE MONTHLY.

our human point of view is that of supposing human intelligence to
be the only kind of intelligence in existence. The fact is, that what
we call the lower animals have special intelligence. of their own as far
transcending our intelligence as our peculiar reasoning intelligence ex-
ceeds theirs. We are as incapable of following the track of a friend
by the smell of his footsteps as a dog is of writing a metaphysical
treatise.

So with insects. They are probably acquainted with a whole world
of physical facts of which we are utterly ignorant. Our auditory ap-
paratus supplies us with a knowledge of sounds. What are these
sounds ? They are vibrations of matter which are capable of produc-
ing corresponding or sympathetic vibrations of the drums of our ears
or the bones of our skull. When we carefully examine the subject,
and count the number of vibrations that produce our world of sounds
of varying pitch, we find that the human ear can only respond to a
limited range of such vibrations. If they exceed three thousand per
second, the sound becomes too shrill for average people to hear it,
though some exceptional ears can take up pulsations, or waves, that
succeed each other more rapidly than this.

Reasoning from the analogy of stretched strings and membranes,
and of air vibrating in tubes, etc., we are justified in concluding that
the smaller the drum or tube the higher will be the note it produces
when agitated, and the smaller and the more rapid the aerial wave to
which it will respond. The drums of insect-ears, and the tubes, etc.,
connected with them, are so minute that their world of sounds prob-
ably begins where ours ceases ; that what appears to us as a continuous
sound is to them a series of separated blows, just as vibrations of ten
or twelve per second appear separated to us. We begin to hear such
vibrations as continuous sounds when they amount to about thirty per
second. The insect's continuous sound probably begins beyond three
thousand. The blue-bottle may thus enjoy a whole world of exquisite
music of which we know nothing.

There is another very suggestive peculiarity in the auditory appa-
ratus of insects. Its structure and position are something between
those of an ear and of an eye. Careful examination of the head of
one of our domestic companions — the common cockroach or black-
beetle — will reveal two round white points, somewhat higher than the
base of the long outer antennae, and a little nearer to the middle line
of the head. These white projecting spots are formed by the outer
transparent membrane of a bag or ball filled with fluid, which ball or
bag rests inside another cavity in the head. It resembles our own eye
in having this external transparent tough membrane which corresponds
to the cornea ; which, like the cornea, is backed by the fluid in the
ear-ball corresponding to our eyeball, and the back of this ear-ball
appears to receive the outspreadings of a nerve, just as the back of
our eye is lined with the dutspread of the optic nerve forming the



ANOTHER WORLD DOWN HERE. 45

retina. There does not appear to be in this or other insects a tightly
stretched membrane which, like the membrane of our ear-drum, is
fitted to take up bodily air-waves and vibrate responsively to them.
But it is evidently adapted to receive and concentrate some kind of
vibration or motion or tremor.

What kind of motion can this be ? What kind of perception does
this curious organ supply ? To answer these questions we must travel
beyond the strict limits of scientific induction and enter the fairy-land
of scientific imagination. We may wander here in safety, provided
we always remember where we are, and keep a true course guided by
the compass-needle of demonstrable facts.

I have said that the cornea-like membrane of the insect's ear-bag
does not appear capable of responding to bodily air-waves. This ad-
jective is important, because there are vibratory movements of matter
that are not bodily but molecular. An analogy may help to render
this distinction intelligible. I may take a long string of beads and
shake it into- wave-like movements, the waves being formed by the
movements of the whole string. We may now conceive another kind
of movement or vibration by supposing one bead to receive a blow
pushing it forward, this push to be communicated to the next, then to
the third, and so on, producing a minute running tremor passing from
end to end. This kind of action may be rendered visible by laying a
number of billiard-balls or marbles in line and bowling an outside ball
against the end one of the row. The impulse will be rapidly and in-
visibly transmitted all along the line, and the outer ball will respond
by starting forward.

Heat, light, and electricity, are mysterious internal movements of
what we call matter (some say " ether," which is but a name for im-
aginary matter). These internal movements are as invisible as those
of the intermediate billiard-balls ; but if there be a line of molecules
acting thus, and the terminal one strikes an organ of sense fitted to
receive its motion, some sort of perception may follow. When such
movements of certain frequency and amplitude strike our organs of
vision, the sensation of light is produced. When others of greater
amplitude and smaller frequency strike the terminal outspread of our
common sensory nerves, the sensation of heat results. The difference
between the frequency and amplitude of the heat-waves and the light-
Avaves is but small, or, strictly speaking, there is no actual line of sep-
aration lying between them ; they run directly into each other. When
a piece of metal is gradually heated, it is first " black-hot " ; this is
while the waves or molecular tremblings are of a certain amplitude
and frequency ; as the frequency increases, and amplitude diminishes
(or, to borrow from musical tenns, as the pitch rises), the metal be-
comes dull red-hot ; greater rapidity, cherry-red ; greater still, bright-
red ; then yellow-hot and white-hot : the luminosity growing as the
rapidity of molecular vibration increases.



46 THE POPULAR SCIENCE MOXTHLY.

There is no such gradation between the most rapid undulations or
tremblings that produce our sensation of sound and the slowest of
those which give rise to our sensations of gentlest warmth. There is
a huge gap between them, wide enough to include another world or
several other worlds of motion, all lying between our world of sounds;
and our world of heat and light, and there is no good reason whatever
for supposing that matter is incapable of such intermediate activity,
or that such activity may not give rise to intermediate sensations, pro-
vided there are organs for taking up and sensifying (if I may coin a
desirable word) these movements.

As already stated, the limit of audible tremors is three to four
thousand per second, but the smallest number of tremors that we can
perceive as heat is between three and four millions of millions per
second. The number of waves producing red light is estimated at
four hundred and seventy-four millions of millions per second ; and
for the production of violet light, six hundred and ninety-nine millions
of millions. These are the received conclusions of our best mathe-
maticians, which I repeat on their authority. Allowing, however, a
very large margin of possible error, the world of possible sensations
lying between those produced by a few thousands of waves and any
number of millions is of enormous width.

In such a world of intermediate activities the insect probably lives,
with a sense of vision revealing to him more than our microscopes
show to us, and with his minute eye-like ear-bag sensifying material
movements that lie between our world of sounds and our other far-
distant worlds of heat and light.

There is yet another indication of some sort of intermediate sen-
sation possessed by insects. JMany of them are not only endowed with
the thousands of lenses of their compound eyes, but have in addition
several curious organs that have been designated " ocelli " and " stem-
mata." These are generally placed at the top of the head, the thou-
sand-fold eyes being at the sides. They are very much like the audi-
tory organs above described — so much so, that in consulting different
authorities for special information on the subject I have fallen into
some confusion, from which I can only escape by supposing that the
organ which one anatomist describes as the ocelli of certain insects is
regarded as the auditory apparatus when examined in another insect
by another anatomist. All this indicates a sort of continuity of sen-
sation connecting the sounds of the insect world with the objects of
their vision.

But these ocular ears or auditory eyes of the insect are not his
only advantages over us. He has another sensory organ to which,
with all our boasted intellect, we can claim nothing that is comparable,
unless it be our olfactory nerve. The possibility of this I will pres-
ently discuss.

I refer to the antennce, which are the most characteristic of insect



ANOTHER WORLD DOWX HERE. 47

organs, and Avondei'fully developed in some, as may be seen by exam-
ining the plumes of the crested gnat. Everybody who has carefully
watched the doings of insects must have observed the curiously investi-
gative movements of the antennae, which are ever on the alert peering
and prying to right and left and upward and downward. Huber, who
devoted his life to the study of bees and ants, concluded that these
insects converse with each other by movements of the antenna?, and
he has given to the signs thus produced the name of " antennal lan-
ccuage." They certainly do communicate information or give orders
by some means ; and, when they stop for that purpose, they face each
other and execute peculiar wavings of these organs that are highly
sugestive of the movements of the old semaphore-telegraph arms.
, The most generally received opinion is, that these antennae are very
delicate organs of touch, but some recent experiments made by Gustav
Plausen indicate that they are organs of smelling or of some similar
power of distinguishing objects at a distance. Flies deprived of their
antennte ceased to display any interest in tainted meat that had pre-
viously proved very attractive. Other insects similarly treated appear
to become indifferent to odors generally. He shows that the develop-
ment of the antennae in different species corresponds to the power of
smelling which they seem to possess.

I am sorely tempted to add another argument to those brought
forward by Hansen, viz., that our own olfactory nerves, and those of
all our near mammalian relations, are curiously like a pair of antennae.

There are two elements in a nervous structure — the gray and the
white ; the gray or ganglionic portion is supposed to be the center or
seat of nervous power, and the white medullary or fibrous portion
merely the conductor of nervous energy.

The nerves of the other senses have their ganglia seated internally,
and the bundles of tubular white threads spread outward therefrom,
but not so with the olfactory nervous apparatus. There are two horn-
like projections thrust forward from the base of the brain, with white
or medullary stems that terminate outwardly or anteriorly in gan-
glionic bulbs resting upon what I may call the roof of the nose, and
throwing out fibers that are composed, rather paradoxically, of more
gray matter than white. In some quadrupeds with great power of
smell, these two nerves extend so far forward as to protrude beyond
the front of the hemispheres of the brain, with bulbous terminations
relatively very much larger than those of man.

They thus appear like veritable antennae. In some of our best
works on anatomy of the brain (Solly, for example) a series of com-
parative pictures of the brains of different animals is shown, extend-
ing from man to the codfish. As we proceed downward, the horn-
like projection of the olfactory nerves beyond the central hemispheres
goes on extending more and more, and the relative magnitude of the
terminal ganglia or olfactory lobes increases in similar order.



48 THE POPULAR SCIENCE MONTHLY.

We have only to omit the nasal bones and nostrils, to continue
this forward extrusion of the olfactory nerves and their bulbs and
branches, to coat them with suitable sheaths provided with muscles
for mobility, and we have the antennae of insects. I submit this view
of the comparative anatomy of these organs as my own speculation, to
be taken for what it is worth.

There is no doubt that the antenna? of these creatures are connected
by nerve-stalks with the anterior part of their supra-a'soi^hageal gan-
glia — i. e., the nervous centers corresponding to our brain.

But what kind and degree of power must such olfactory organs
possess ? The dog has, relatively to the rest of his brain, a much
greater development of the olfactory nerves and ganglia than man has.
His powers of smell are so much greater than ours that we find it dif-
ficult to conceive the possibility of what we actually see him do. As
an example, I may describe an experiment I made upon a blood-hound
of the famous Cuban breed. He belonged to a friend whose house is
situated on an eminence commanding an extensive view. I started
from the garden and wandered about a mile away, crossed several fields
by sinuous courses, climbing over stiles and jumping ditches, always
keeping the house in view ; I then returned by quite a different track.
The blood-hound was set upon the beginning of my track. I watched
him from a window galloping rapidly, and following all its windings
without the least halting or hesitation. It was as clear to his nose as
a graveled path or a luminous streak would be to our eyes. On his
return I went downi to him, and without approaching nearer than five
or six yards he recognized me as the object of his search, proving this
by circling round me, baying deeply and savagely though harmlessly,
as he always kept at about the same distance.

If the difference of development between the human and canine
internal antennae produces all this difference of function, what a gulf
may there be between our powers of perceiving material emanations
and those possessed by insects ! If my anatomical hypothesis is cor-
rect, some insects have protruding nasal organs or out-thrust olfactory
nerves as long as all the rest of their bodies. The power of movement
of these in all directions affords the means of sensory communication
over a coiTcsponding range, instead of being limited merely to the
direction of the nostril-openings. In some Insects, such as the plumed
gnat, the antennae do not appear to be thus movable, but this want of
mobility is more than compensated by the multitude of branchings of
these wonderful organs whereby they are simultaneously exposed in
every direction. This structure is analogous to the fixed but multi-
plied eyes of insects, which, by seeing all round at once, compensate
for the want of that mobility possessed by others that have but a single
eyeball mounted on a flexible and mobile stalk ; that of the spider, for
example.

Such an extension of such a sensory function is equivalent to liv-



r



ORIGIN AND STRUCTURE OF VOLCANIC CONES. 49

ing in another world of which we have no knowledge and can form no
definite conception. We, by our senses of touch and vision, know the
shapes and colors of objects, and by our very rudimentary olfactory
organs form crude ideas of their chemistry or composition, through the
medium of their material emanations ; but the huge exaggeration of
this power in the insect should supply him with instinctive perceptive
[towers of chemical analysis, a direct acquaintance with the inner mo-
lecular constitution of matter far clearer and deeper than we are able
to obtain by all the refinements of laboratory analyses or the hypo-
thetical formulating of molecular mathematicians. Add this to the
other world of sensations producible by the vibratory movements of
matter lying between those perceptible by our organs of hearing and
vision, then strain your imagination to its cracking-point, and you will
still fail to picture the wonder-land in which the smallest of our fellow-
creatures may be living, moving, and having their being. — Belgravia.



THE ORIGIN AXD STRUCTUEE OF VOLCANIC
CONES.

Br H. J. JOKN'STON-LAVIS, F. G. S. ^
II.

IT is observable in certain volcanoes that the lava frequently strewed
around after an eruption contains more or less perfect spheres,
consisting of a hard external coat and more scoriaceous contents, and
these from their resemblance are known as volcanic bombs. Their
contents may be divided into two classes :

1. Scoriaceous vesicular lava, identical in composition with the ex-
ternal shell.

2. Miscellaneous, such as altered masses of lapilli, loose blocks of
foreign materials caught up in the current of lava. These balls are
generally considered to be formed by the masses being ejected to
^reat heights, and cooling as they whirl through the atmosphere.

This seems improbable, as on falling they would inevitably smash
into a thousand fragments. It would appear more likely that they
are simply concretionary in structure around a nucleus of low tempera-
ture, solidifying on the surface a layer forming a crust of lava. Let
us now direct our attention to the minor particulars, such as the
changes of the crater, and metamorphism, or alteration of the already
ejected materials. If the volcano has already reached some consider-
able dimensions, effected by one or many eruptions, we shall find that
certain definite changes have taken place in the chimney. The erup-
tion is reduced in force, there are spasmodic puff-lika ejections of la-

TOL. SIX. — 4







THE POPULAR SCIENCE MONTHLY.



pilli, and occasionally small streams of lava emitted. Before entering
further into our subject, we must return a step or two. It has been
mentioned that the inclination of the outer slope of the cone is that of
the " angle of repose " of the rock-fragments. We should, therefore,



PONTA KflSDNE




Fig. 1.— a. Cone op Eruption built up in the Crater op 1878: B. Vesuvius proper, this cone
composed of alternate lava-streamn b, and lapiili a, built up since a. d. 79. It occupies' the
crater of Somma ; C. This is composed like the latter, of alternate beds of lava c' and lapiili c;
B, C. Deposits of pumice and trachytic frapments, etc., capping all exposed parti? of 8omma
derived from the eniption of a. d. 79 ; D. Beds of late Tertiary period containing shells exist-
ing at present in the Mediterranean ; E. Basis, consiBting of denuded surface of Apennine
limestone (cretaceous ?) ; F. Chimney or vent.

conclude that the inner or chimney side would be much the same.
This, however, is not generally the case, the inner retaining a greater
slope than the outer. It is due chiefly to the fusion, or cementing to-
gether, of the fragments by the intense heat and the presence of lava,
which, so to speak, solders each mass to its neighbor. Each is re-
tained in position by the fluid column occupying the internal cavity,
and when this has disappeared the temperature is necessarily lowered,
and thus there is formed a lining to the tube by the semifusion of its
superficial components. Nevertheless, the upper edges crumble away,
falling into the vents, thence to be again ejected. This process con-
tinually repeated will result in the majority of the lapiili falling on
the outer slope, leaving the chimney of the form of a true funnel, that
is to say, a cavity whose sides descend for a certain distance at a mod-
erate angle, say roughly 45°, and then suddenly increasing to nearly
a perpendicular. The consequence of this is, a basin-like cavity of
sloping walls, with the volcanic vent situated at its center. The ma-
terials now ejected by the volcano, supposing it to be in a compara-
tively quiescent state, will tend to build up a fresh cone occupying
this basin. It is not a thing unknown for such a concentric arrange-
ment of cones and craters to be extended to many repetitions. Let us
take for example the crater of Somma (Fig. 1) occupied by the cone
of Vesuvius, and this again inclosing within its own walls the little
cone of eruption, A. We may perhaps represent it thus : A : B : : B : C.



ORIGIN AND STRUCTURE OF VOLCANIC CONES. 51

Such a repetition is recoydecl as being quadruple, thus giving to the
mountain, near its apex, a step-like appearance.

From various irregularities and accidents, the vent may shift its
position and become eccentric, and thus produce an overlapping of the
newer cone upon the older. This is well illustrated by the Island of
Vulcano at this moment. In fact, the little hill of scoria surrounding
the active bocca or mouth of Vesuvius is situated right away to the
east-northeast of the crater, and consequently the lava-streams are
more abundant on that side of the mountain (Fig. 2).

The escape of the lava and vapor is the next thing to require our
attention. Little more, however, has to be said. The lava rarely
mounts the edge of the cone of eruption, generally escaping near its
foot, by forcing itself a passage through the loose materials or some
preexisting fissure according to hydrostatical laws. The vapor is the
real agent in keeping a vent clear, as the vast bubbles rise through the
viscid mass, bursting at its surface, thus keeping up the temperature
of the lava-column which it has traversed by the heat brought up
from below, and at the same time preventing any permanent stag-
nation therein. The vapor is generally to be seen carried away by
•the wind in beautiful white clouds. When, however, the eruption is
of a more intense kind, these vast volumes mount into the air at great
heights, appearing like a column of fire by night, carrying with them
lapilli and ash often thousands of feet above the mouth of the volcano ;




5

'""'■'"■ ' 5

Fio. 2.— View op the Cbateb of Vescvius, as seen from the Hiohebt Point of Monte Somma,
ON JcLV 1, 1880: A. Crater ; B. Cone of eruption ; C. Slopes of cone. 1. Spire-like fumarole;
8. Irregular fumaroles alonsj a fissure ; 3. Bocca- Grande, or vent ; 4. Edges and walls of crater
(full) ; 6. Ash-beda composing cone ; 6. Cooled lava-streams all thrown out since November,



Online LibraryD. S. (David Samuel) MargoliouthThe Popular science monthly (Volume 19) → online text (page 6 of 110)