SCIENCE IN THE OPEN AIR—APHIDES—EVAPORATION BY LEAVES—AN AQUARIUM—THE
CATALEPTIC FOWL—NEEDLE POINTS AND THORNS—MICROSCOPIC AQUARIUM—CAPE
GRISNEZ—CRYSTALS—ICE ON THE GAS LAMPS.
[Illustration: Fig. 1.—Ants engaged in extracting aphides from a
rose-tree (highly magnified)]
Some years ago we were staying in Normandy, not far from the town
of C——, enjoying, in the midst of most cordial hospitality, the
peacefulness of country life; and my kind hosts, with me, took great
pleasure in having what we called “a course of science in the open
air.” The recollections of that time are some of the pleasantest in
the whole course of my life, because all our leisure was intelligently
occupied. Each of us set himself to provide the subject of some curious
observation or instructive experiment; one made a collection of
insects, another studied botany. In the daytime we might have been seen
examining, under a magnifying glass, the branch of a rose-tree, from
which the ants were endeavouring to extract the aphides[1] (fig. 1).
At night we admired through the telescope the stars and planets that
were visible; or if the sky was not clear, we examined under a strong
magnifier grains of pollen from flowers, or the _infusoria_ in a drop
of stagnant water. Frequently some very insignificant object became
the occasion for some scientific discussion, which terminated with an
experimental verification.
I recollect that one day one of us remarked that after a week of dry
weather a stream of water had nearly dried up, although sheltered by
thick trees, which necessarily impeded the calorific action of the sun;
and he expressed surprise at the rapid evaporation. An agriculturist
among the company, however, drew his attention to the fact that the
roots of the trees were buried in the course of the stream, and that,
far from preventing the evaporation of the water, the leaves had
contributed to accelerate it. As the first speaker was not convinced,
the agriculturist, on our return to the house, prepared an experiment
represented in fig. 2. He placed the branch of a tree covered with
foliage in a U-shaped tube, the two branches of unequal diameter, and
filled with water. He placed the vegetable stem in the water, and
secured it to the tube by means of a cork covered with a piece of
india-rubber, and tied tightly to make it hermetically closed.
[Illustration: Fig. 2.—Experiment showing evaporation of water by
leaves.]
At the commencement of the experiment the water was level with A in
the larger branch of the tube, and level with B in the smaller, rising
by capillarity to a higher point in the more slender of the two. The
evaporation of the water caused by the leaves was so active that in a
very short time we beheld the water sink to the points C and C′.
[Illustration: Fig. 3.—Aquarium formed by means of a melon glass.]
Thus did the excellent method of seeking the cause of phenomena by
experiments often lead us to interesting results. We had among us many
children and young people who had reached the age of ardent curiosity.
We took pleasure in pointing out to them the means of studying natural
science; and we were not long before feeling convinced that our lessons
out in the fields had much greater success than those given between
the four walls of a class-room. Insects were collected, and preserved
by being carefully placed in a small bottle, into which was let fall a
drop of sulphuret of carbon;[2] the insect was immediately asphyxiated,
and we thus avoided the cruelty of passing a pin through a living
body. Having chased butterflies and insects, we next desired to study
the aquatic creatures which swarmed in the pools of the neighbourhood.
For this purpose I constructed a fishing-net fitted to an iron ring,
and firmly secured to a wooden handle. When this was plunged under the
water and drawn quickly out again, it came back full of slime. In the
midst of this muddy substance one generally succeeded in finding the
hydrophilus, tadpoles, coleoptera, many curious kinds of caddis-worms,
tritons, and sometimes frogs, completely astounded by the rapidity of
their capture. All these creatures were transported in a bottle to the
house, and I then constructed, at small expense, a glass aquarium, by
means of the bell of a melon-glass turned upside down, thus forming a
transparent receptacle of considerable size. Four wooden stakes were
then fixed in the ground, and a plank with a circular hole nailed on
the top, in which the glass bell was placed. I next scattered some
large pebbles and shells at the bottom of the vase to form a stony bed,
poured in some water, placed a few reeds and water plants among the
pebbles, and then threw a handful of water lentils on the surface;
thus a comfortable home was contrived for all the captured animals.[3]
The aquarium, when placed under the shade of a fine tree in a rustic
spot abounding with field flowers, became a favourite rendezvous, and
we often took pleasure in watching the antics of the little inmates
(fig. 3). Sometimes we beheld very sanguinary scenes; the voracious
hydrophilus would seize a poor defenceless tadpole, and rend him in
pieces for a meal without any compunction. The more robust tritons
defended themselves better, but sometimes they also succumbed in the
struggle.
[Illustration: Fig. 4.—Cage for preserving living insects.]
[Illustration: Fig. 5.—Small aquarium, with frogs’ ladder.]
The success of the aquarium was so complete that one of us resolved to
continue this museum in miniature, and one day provided himself with an
_insects palace_, which nearly made us forget the tadpoles and tritons.
It was a charming little cage, having the form of a house, covered
with a roof; wires placed at equal distances forming the sides. In it
was a large cricket beside a leaf of lettuce, which served as his food
(fig. 4). The little creature moved up and down his prison, which was
suspended from the branch of a tree, and when one approached him very
closely gave vent to his lively chirps.
[Illustration: Fig. 6.—Frog lying in wait for a fly.]
The menagerie was soon further augmented by a hitherto unthought-of
object; namely, a frogs’ ladder. It was made with much skill. A large
bottle served for the base of the structure. The ladder which was fixed
in it was composed of the twigs of very small branches, recently cut
from a tree, and undivested of their bark, which gave to the little
edifice a more picturesque and rustic appearance. The pieces of wood,
cleverly fixed into two posts, conducted the green frogs (tree-frogs)
on to a platform, whence they ascended the steps of a genuine ladder.
There they could disport themselves at pleasure, or climb up further
to a branch of birch-tree placed upright in the centre of the bottle
(fig. 5). A net with fine meshes prevented the little animals from
escaping. We gave the tree-frogs flies for their food, and sometimes
they caught them with remarkable dexterity. I have often seen a frog
when at liberty watching a fly, on which it pounces as a cat does on
a bird (fig. 6). The observations that we made on the animals of our
menagerie led us to undertake others of a very different nature; I
recollect particularly a case of catalepsy produced in a cock. I will
describe this remarkable experiment, certainly one of the most curious
we ever performed.
[Illustration: Fig. 7.—Experiment of the cataleptic cock.]
We place a cock on a table of dark colour, rest its beak on the
surface, where it is firmly held, and with a piece of chalk slowly draw
a white line in continuation from the beak, as shown in our engraving.
If the crest is thick, it is necessary to draw it back, so that the
animal may follow with his eyes the tracing of the line. When the line
has reached a length of about two feet the cock has become cataleptic.
He is absolutely motionless, his eyes are fixed, and he will remain
from thirty to sixty seconds in the same posture in which he had at
first only been held by force. His head remains resting on the table
in the position shown in fig. 7. This experiment, which we have
successfully performed on different animals, can also be accomplished
by drawing a straight line with a piece of chalk on a slate. M. Azam
declares that the same result is also produced by drawing a black line
on a table of white wood. According to M. Balbiani, German students had
formerly a great predilection for this experiment, which they always
performed with marked success. Hens do not, when operated on, fall
into a cataleptic condition so easily as cocks; but they may often be
rendered motionless by holding their heads fixed in the same position
for several minutes. The facts we have just cited come properly under
the little studied phenomena, designated by M. Braid in 1843 by the
title of _Hypnotism_. MM. Littré and Ch. Robin have given a description
of the hypnotic condition in their _Dictionnaire de Médecine_.
[Illustration: Fig. 8.—Ordinary pin and needle, seen through a
microscope (magnified 500 diameters).]
[Illustration: Fig. 9.—Thorn of a rose, and wasp’s sting through a
microscope (magnified 500 diameters).]
If any shining object, such as a lancet, or a disc of silver-paper
gummed to a plate, is placed at about the distance of a foot from the
eyes of a person, slightly above the head, and the patient regards
this object fixedly, and without interruption for twenty or thirty
minutes, he will become gradually motionless, and in a great number
of cases will fall into a condition of torpor and genuine sleep. Dr.
Braid affirms that under such circumstances he has been able to perform
surgical operations, without the patient having any consciousness of
pain. Later also, M. Azam has proved the complete insensibility to
pricking on the part of individuals whom he has rendered cataleptic by
the fixing of a brilliant object. The experiment of the cataleptic
cock was first described under the name of _Experimentum Mirabile_,
by P. Kircher, in his _Ars Magna_, published at Rome in 1646. It
evidently belongs to the class of experiments which were performed
at the Salpêtrière asylum at Paris, by M. Charcot, on patients
suffering from special disorders. It must now be evident to our
readers that our scientific occupations were sufficiently varied,
and that we easily found around us many objects of study. When the
weather was wet and cloudy we remained indoors, and devoted ourselves
to microscopical examinations. Everything that came under our hands,
insects, vegetables, etc., were worthy of observation. One day, while
engaged over a microscopical preparation, I was making use of one of
those steel points generally employed in such purposes, when happening
to pass it accidentally beneath the microscope, I was astonished to
see how rough and uneven it appeared when highly magnified. The idea
then occurred to me to have recourse to something still more pointed,
and I was thus led to make comparisons between the different objects
represented in figs. 8 and 9. It will here be seen how very coarse
is the product of our industry when compared with the product of
Nature. No. 1 of fig. 8 represents the point of a pin that has already
been used, magnified 500 diameters. The point is evidently slightly
blunted and flattened. The malleable metal has yielded a little under
the pressure necessary to make it pass through a material. No. 2 is
a little more pointed; it is a needle. This, too, will be seen to be
defective when regarded by the aid of the microscope. On the other
hand, what fineness and delicacy do the rose thorn and wasp’s sting
present when examined under the same magnifier! (See the two points in
fig. 9.)
An examination of this exact drawing has led me to make a calculation
which leads to rather curious results: at a half millimetre from the
point, the diameters of the four objects represented are in thousandths
of a millimetre respectively, 3·4; 2·2; 1·1; 0·38. The corresponding
sections in millionths of a square millimetre are: 907·92; 380·13;
95·03; 11·34; or, in round numbers, 908; 380; 95; 11.
If one bears in mind, which is much below the truth, that the pressure
exercised on the point must be proportional to the section, and
admitting that a pressure of 11 centigrams suffices to thrust in the
sting of a wasp half a millimetre, it will require more than 9 grams
of pressure to thrust in a needle to the same extent. In fact, this
latter figure is much too small, for we have not taken into account the
advantage resulting from the elongated shape of the rose thorn, which
renders it more favourable for penetration than a needle through a drop
of tallow.
It would be easy to extend observations of this kind to a number
of other objects, and the remarks I have just made on natural and
artificial points will apply incontestably to textures for example.
There is no doubt that the thread of a spider’s web would far surpass
the thread of the finest lace, and that art will always find itself
completely distanced by nature.
We amused ourselves frequently by examining the _infusoria_ which are
so easily procured by taking from some stagnant water the mucilage
adhering to the vegetation on the banks, or attached to the lower part
of water lentils. In this way we easily captured _infusoria_, which,
when placed under a strong magnifier, presented the most remarkable
spectacle that one can imagine. They are animalcules, having the form
of transparent tulips attached to a long stem. They form bunches
which expand and lengthen; then, suddenly, they are seen to contract
with such considerable rapidity that the eye can scarcely follow the
movement, and all the stems and flower-bells are folded up into the
form of a ball. Then, in another moment, the stems lengthen, and the
tulip-bells open once more. One can easily encourage the production
of _infusoria_ by constructing a small microscopic aquarium, in which
one arranges the centre in a manner favourable to the development of
the lowest organisms. It suffices to put a few leaves (a piece of
parsley answers the purpose perfectly)[4] in a small vase containing
water (fig. 10), over which a glass cover is placed, and it is then
exposed to the rays of the sun. In two or three days’ time, a drop of
this water seen under the microscope will exhibit _infusoria_. After a
certain time, too, the different species will begin to show themselves.
Microscopical observations can be made on a number of different
objects. Expose to the air some flour moistened by water, and before
long a mouldiness will form on it; it is the _penicillium glaucum_,
and when examined under a magnifier of 200 to 300 diameters, cells are
distinguishable, branching out from an organism remarkable for its
simplicity. We often amused ourselves by examining, almost at hazard,
everything that came within our reach, and sometimes we were led to
make very instructive investigations. When the sky was clear, and the
weather favourable to walking, we encouraged our young people to run
about in the fields and chase butterflies. The capture of butterflies
is accomplished, as every one knows, by means of a gauze net, with
which we provided the children, and the operation of chasing afforded
them some very salutary exercise. It sometimes happens that butterflies
abound in such numbers, that it is comparatively easy to capture them.
During the month of June 1879, a large part of Western Europe was
thronged with swarms of _Vanessa algina_ butterflies, in such numbers
that their appearance was regarded as an important event, and attracted
the lively attention of all entomologists (fig. 11). This passage of
butterflies provided the occasion for many interesting studies on the
part of naturalists.
[Illustration: Fig. 10.—Arrangement of a microscopic aquarium for
examining _infusoria_.]
[Illustration: Fig. 11.—Flight of butterflies seen near Berne, June
15th, 1879.]
[Illustration: Fig. 12.—Group of rock crystal.]
We cannot point out too strongly to our readers that the essential
condition for the student of natural science, is the possession of
that sacred fire which imparts the energy and perseverance necessary
for acquiring and enlarging collections. It is also necessary that
the investigator should furnish himself with certain indispensable
tools. For collecting plants, the botanist should be armed with a
pickaxe set in a thoroughly strong handle, a trowel, of which there
is a variety of shapes, and a knife with a sharp blade. A botanical
case must also be included, for carrying the plants. The geologist,
or mineralogist, needs no more elaborate instruments; a hammer, a
chisel, and a pickaxe with a sharp point for breaking the rocks, and a
bag for carrying the specimens, will complete his outfit. We amused
ourselves by having these instruments made by the blacksmith, sometimes
even by manufacturing them ourselves; they were simple, but solid, and
admirably adapted to the requirements of research. Often we directed
our walks to the seashore, where we liked to collect shells on the
sandy beach, or fossils among the cliffs and rocks. I recollect, in a
walk I had taken some years previously along the foot of the cliffs of
Cape Blanc-Nez, near Calais, having found an impression of an ammonite
of remarkable size, which has often excited the admiration of amateurs;
this ammonite measured no less than twelve inches in diameter. The
rocks of Cape Grisnez, not far from Boulogne, also afford the geologian
the opportunity of a number of curious investigations. In the Ardennes
and the Alps I have frequently procured some fine mineral specimens; in
the first locality crystallized pyrites, in the second, fine fragments
of rock crystal (fig. 12). I did not fail to recount these successful
expeditions to the young people who accompanied me, and their ardour
was thereby inflamed by the hope that they also should find something
valuable. It often happened when the sun was powerful, and the air
extremely calm, that my young companions and I remarked some very
beautiful effects of mirage on the beach, due to the heating of the
lower _strata_ of the atmosphere. The trees and houses appeared to
be raised above a sheet of silver, in which their reflections were
visible as in a sheet of tranquil water. It can hardly be believed how
frequently the atmosphere affords interesting spectacles which pass
unperceived before the eyes of those who know not how to observe. I
recollect having once beheld at Jersey a magnificent phenomenon of
this nature, on the 24th June, 1877, at eight o’clock in the evening:
it was a column of light which rose above the sinking sun like a
sheaf of fire. I was walking on the St. Helier pier, where there were
also many promenaders, but there were not more than two or three who
regarded with me this mighty spectacle. Columns and crosses of light
are much more frequent than is commonly supposed, but they often
pass unperceived before indifferent spectators. We will describe an
example of this phenomenon observed at Havre on the 7th May, 1877.
The sun formed the centre of the cross, which was of a yellow, golden
colour. This cross had four branches. The upper branch was much more
brilliant than the others; its height was about 15°. The lower branch
was smaller, as seen in the sketch on page 2, taken from nature by
Monsieur Albert Tissandier. The two horizontal branches were at times
scarcely visible, and merged in a streak of reddish-yellow colour,
which covered a large part of the horizon. A mass of cloud, which the
setting sun tinged with a deep violet colour, formed the foreground of
the picture. The atmosphere over the sea was very foggy. The phenomenon
did not last more than a quarter of an hour, but the conclusion of
the spectacle was signalized by an interesting circumstance. The two
horizontal branches, and the lower branch of the luminous cross,
completely disappeared, whilst the upper branch remained alone for some
minutes longer. It had now the appearance of a _vertical column_ rising
from the sun, like that which Cassini studied on the 21st May, 1672,
and that which M. Renon[5] and M. A. Guillemin observed on the 12th
July, 1876.[6] Vertical columns, which, it is well known, are extremely
rare phenomena, may therefore indicate the existence of a luminous
cross, which certain atmospheric conditions have rendered but partially
visible.
How often one sees along the roads little whirlwinds of dust raised
by the wind accomplishing a rotatory movement, thus producing the
imitation of a waterspout! How often halos encompass with a circle of
fire the sun or the stars! How often we see the rainbow develop its
iridescent beauties in the midst of a body of air traversed by bright
raindrops! And there is not one of these great natural manifestations
which may not give rise to instructive observations, and become the
object of study and research. Thus, in walks and travels alike, the
study of Science may always be exercised; and this method of study and
instruction in the open air contributes both to health of body and
of mind. As we consider the spectacles which Nature spreads before
us,—from the insect crawling on the blade of grass, to the celestial
bodies moving in the dome of the heavens,—we feel a vivifying and
salutary influence awaken in the mind. The habit of observation, too,
may be everywhere exercised—even in towns, where Nature still asserts
herself; as, for example, in displays of meteorological phenomena. We
will give an example of such.
[Illustration: Fig. 13.—Icicles on gas lamp.]
The extraordinary abundance of snow which fell in Paris for more than
ten consecutive hours, commencing on the afternoon of Wednesday,
January 22nd, 1880, will always be looked upon as memorable among
the meteorological events of the city of Paris. It was stated that
in the centre of Paris, the thickness of the snow that had fallen at
different times exceeded fourteen inches. The snow had been preceded by
a fall of small transparent icicles, of rather more than a millimetre
in diameter, some having crystalline facets. They formed on the
surface of the ground a very slippery glazed frost. On the evening
of the 22nd January, flakes of snow began to hover in the atmosphere
like voluminous masses of wool. The greater part of the gas-lamps
were ornamented by frozen stalactites, which continually attracted
the attention of passers-by. The formation of these stalactites, of
which we give a specimen (fig. 13), is easy of explanation. The snow
falling on the glass of the lamp became heated by the flame of gas,
melted, and trickled down, freezing anew into the shape of a stalactite
below the lamp, at a temperature of 0° centigrade. Not only can
meteorology be studied in towns, but certain other branches of natural
science—entomology, for example. We will quote what a young student
in science, M. A. Dubois, says on this very subject: “Coleoptera,”
he declares, “are to be met with everywhere, and I think it may be
useful to notice this fact, supporting it by examples. I desire to
prove that there are in the midst of our large towns spots that remain
unexplored, where some fine captures are to be made. Let us visit, at
certain times, the approaches to the quays, even at low tide, and we
shall be surprised to find there species which we have searched for
far and near.” This opinion is confirmed by the enumeration of several
interesting captures.
Was not the great Bacon right when he said, “For the keen observer,
nothing in Nature is mute”?
[Illustration: The cliffs of Cape Grisnez.]
FOOTNOTES:
[1] It is well known that ants, by touching the skin of aphides,
extract therefrom a secretion of viscous matter, which nourishes them.
They will frequently carry off the aphides to their habitations, and
keep them there; thus one may say they _keep a cow in their stable_.
[2] The preservation of insects, and their preparation for collections,
necessitates some precaution. Entomologists are in the habit of
spreading them out on a small board, and arranging the legs and
_antennæ_ by means of large pins. The wings should be dried by placing
them on strips of paper, which preserves them. These precautions are
indispensable if it is wished that the insects in a collection should
retain their distinctive characters. Worms and caterpillars can be
raised in pots filled with earth, if carefully covered over with muslin
or wire gauze with very fine meshes. The process of hatching may give
rise to many interesting observations.
[3] It frequently happens that in a small aquarium, constructed after
this fashion, the animals escape. This is avoided by covering the vase
with a net.
[4] The infusion of parsley has the advantage of not sensibly obscuring
the water.
[5] Detailed accounts in Vol. lxxxiii., pp. 243 and 292 of “_La
Nature_.”
[6] See “_La Nature_,” 4th year, 1876, 2nd half-year, p. 167. M. A.
Guillemin mentions, in connection with the phenomenon of July 12th,
1876, the presence of light masses of cloud of a greyish-blue colour,
similar to those perceived in the phenomena just described.