suggest at first view a book, or better a book cover, seen with its
back toward you and its sides sloping away from you; but it may also
be viewed as a book opened out toward you and presenting to you an
inside view of its contents. Should the change not come readily, it
may be facilitated by thinking persistently of the appearance of an
open book in this position. The upper portion of Fig. 9 is practically
the same as Fig. 8, and if the rest of the figure be covered up, it
will change as did the book cover; when, however, the whole figure is
viewed as an arrow, a new conception enters, and the apparently solid
book cover becomes the _flat_ feathered part of the arrow. Look at the
next figure (Fig. 10), which represents in outline a truncated pyramid
with a square base. Is the smaller square nearer to you, and are the
sides of the pyramid sloping away from you toward the larger square in
the rear? Or are you looking into the hollow of a truncated pyramid
with the smaller square in the background? Or is it now one and now
the other, according as you decide to see it? Here (Fig. 13) is a
skeleton box which you may conceive as made of wires outlining the
sides. Now the front, or side nearest to me, seems directed downward
and to the left; again, it has shifted its position and is no longer
the front, and the side which appears to be the front seems directed
upward and to the right. The presence of the diagonal line makes the
change more striking: in one position it runs from the left-hand
_rear_ upper corner to the right-hand _front_ lower corner; while in
the other it connects the left-hand _front_ upper corner with the
right-hand _rear_ lower corner.
[Illustration: FIGS. 13, 13_a_, and 13_b_.--The two methods of viewing
Fig. 13 are described in the text. Figs. 13_a_ and 13_b_ are added to
make clearer the two methods of viewing Fig. 13. The heavier lines
seem to represent the nearer surface. Fig. 13_a_ more naturally
suggests the nearer surface of the box in a position downward and to
the left, and Fig. 13_b_ makes the nearer side seem to be upward and
to the right. But in spite of the heavier outlines of the one surface,
it may be made to shift positions from foreground to background,
although not so readily as in Fig. 13.]
[Illustration: FIG. 14.--Each member of this frieze represents a
relief ornament, applied upon the background, which in cross-section
would be an isosceles triangle with a large obtuse angle, or a space
of similar shape hollowed out of the solid wood or stone. In running
the eye along the pattern, it is interesting to observe how variously
the patterns fluctuate from one of these aspects to the other.]
[Illustration: FIGS. 15, 15_a_, and 15_b_.--The two views of Fig. 15
described in the text are brought out more clearly in Figs. 15_a_ and
15_b_. The shaded portion tends to be regarded as the nearer face.
Fig. 15_a_ is more apt to suggest the steps seen as we ascend them.
Fig. 15_b_ seems to represent the hollowed-out structure underneath
the steps. But even with the shading the dual interpretation is
possible, although less obvious.]
Fig. 15 will probably seen at first glimpse to be the view of a flight
of steps which one is about to ascend from right to left. Imagine it,
however, to be a view of the under side of a series of steps; the view
representing the structure of overhanging solid masonwork seen from
underneath. At first it may be difficult to see it thus, because the
view of steps which we are about to mount is a more natural and
frequent experience than the other; but by staring at it with the
intention of seeing it differently the transition will come, and often
quite unexpectedly.
[Illustration: FIG. 16.--This interesting figure (which is reproduced
with modifications from Scripture--The New Psychology) is subject in a
striking way to interchanges between foreground and background. Most
persons find it difficult to maintain for any considerable time either
aspect of the blocks (these aspects are described in the text); some
can change them at will, others must accept the changes as they happen
to come.]
[Illustration: Fig. 17_a_.]
[Illustration: Fig. 17_b_.]
[Illustration: Fig. 17.
FIGS. 17, 17_a_, and 17_b_.--How many blocks are there in this pile?
Six or seven? Note the change in arrangement of the blocks as they
change in number from six to seven. This change is illustrated in the
text. Figs. 17_a_ and 17_b_ show the two phases of a group of any
three of the blocks. The arrangement of a pyramid of six blocks seems
the more stable and is usually first suggested; but hold the page
inverted, and you will probably see the alternate arrangement (with,
however, the black surfaces still forming the tops). And once knowing
what to look for, you will very likely be able to see either
arrangement, whether the diagram be held inverted or not. This method
of viewing the figures upside down and in other positions is also
suggested to bring out the changes indicated in Figs. 13, 13_a_,
13_b_, and in Figs. 15, 15_a_, 15_b_.]
The blocks in Fig. 16 are subject to a marked fluctuation. Now the
black surfaces represent the bottoms of the blocks, all pointing
downward and to the left, and now the black surfaces have changed and
have become the tops pointing upward and to the right. For some the
changes come at will; for others they seem to come unexpectedly, but
all are aided by anticipating mentally the nature of the
transformation. The effect here is quite striking, the blocks seeming
almost animated and moving through space. In Fig. 17 a similar
arrangement serves to create an illusion as to the real number of
blocks present. If viewed in one way--the black surface forming the
tops of the blocks--there seem to be six arranged as in Fig. 18; but
when the transformation has taken place and the black surfaces have
become the overhanging bottoms of the boxes, there are seven, arranged
as in Fig. 19. Somewhat different, but still belonging to the group of
ambiguous figures, is the ingenious conceit of the duck-rabbit shown
in Fig. 20. When it is a rabbit, the face looks to the right and a
pair of ears are conspicuous behind; when it is a duck, the face looks
to the left and the ears have been changed into the bill. Most
observers find it difficult to hold either interpretation steadily,
the fluctuations being frequent, and coming as a surprise.
[Illustration: FIG. 18.]
[Illustration: FIG. 19.]
[Illustration: FIG. 20.--Do you see a duck or a rabbit, or either?
(From Harper's Weekly, originally in Fliegende Blätter.)]
All these diagrams serve to illustrate the principle that when the
objective features are ambiguous we see one thing or another according
to the impression that is in the mind's eye; what the objective
factors lack in definiteness the subjective ones supply, while
familiarity, prepossession, as well as other circumstances influence
the result. These illustrations show conclusively that seeing is not
wholly an objective matter depending upon what there is to be seen,
but is very considerably a subjective matter depending upon the eye
that sees. To the same observer a given arrangement of lines now
appears as the representation of one object and now of another; and
from the same objective experience, especially in instances that
demand a somewhat complicated exercise of the senses, different
observers derive very different impressions.
Not only when the sense-impressions are ambiguous or defective, but
when they are vague--when the light is dim or the forms obscure--does
the mind's eye eke out the imperfections of physical vision. The vague
conformations of drapery and make-up that are identified and
recognized in spiritualistic _séances_ illustrate extreme instances of
this process. The whitewashed tree or post that momentarily startles
us in a dark country lane takes on the guise that expectancy gives it.
The mental predisposition here becomes the dominant factor, and the
timid see as ghosts what their more sturdy companions recognize as
whitewashed posts. Such experiences we ascribe to the action of
suggestion and the imagination--the cloud "that's almost in shape like
a camel," or "like a weasel," or "like a whale." But throughout our
visual experiences there runs this double strain, now mainly outward
and now mainly inward, from the simplest excitements of the retina up
to the realms where fancy soars freed from the confines of sense, and
the objective finds its occupation gone.
FOOTNOTE:
[5] In order to obtain the effects described in the various
illustrations it is necessary in several cases to regard the figures
for a considerable time and with close attention. The reader is
requested not to give up in case the first attempt to secure the
effect is not successful, but to continue the effort for a reasonable
period. Individuals differ considerably in the readiness with which
they obtain such effects; in some cases, such devices as holding the
diagrams inverted or at an angle or viewing them with the eyes half
closed are helpful.
NATURE STUDY IN THE PHILADELPHIA NORMAL SCHOOL.
BY L. L. W. WILSON, PH. D.
When it was first proposed to me to write for the Popular Science
Monthly a brief account of the biological laboratories in the
Philadelphia Normal School, and of the Nature work carried on under my
direction in the School of Observation and Practice, I felt that I
could not do justice either to the place or the work; for, in my
judgment, the equipment of the laboratories and the work done in
connection with them are finer than anything else of the kind either
in this country or abroad--a statement which it seemed to me that I
could not make with becoming modesty. But, after all, it is not great
Babylon that I have built, but a Babylon builded for me, and to fail
to express my sense of its worth is to fail to do justice to Dr. W. P.
Wilson, formerly of the University of Pennsylvania, to whom their
inception was due; to Mr. Simon Gratz, president of the Board of
Education, who from the beginning appreciated their value, and without
whose aid they never would have taken visible form; to the principals
of the two schools, and, above all, to my five assistants, whose
knowledge, zeal, and hard work have contributed more than anything
else to the rapid building up of the work.
THE LABORATORIES AND THEIR EQUIPMENT.--The rooms occupied by the
botanical and zoölogical departments of the normal school measure each
seventy by twenty feet. A small workroom for the teachers cuts off
about ten feet of this length from each room. In the middle of the
remaining space stands a demonstration table furnished with hot and
cold water. Each laboratory is lighted from the side by ten windows.
From them extend the tables for the students. These give plenty of
drawer space and closets for dissecting and compound microscopes.
Those in the zoölogical room are also provided with sinks. Each
student is furnished with the two microscopes, stage and eyepiece
micrometers, a drawing camera, a set of dissecting instruments,
glassware, note-books, text-books, and general literature.
The walls opposite the windows are in both rooms lined with cases, in
which there is a fine synoptic series.
In the botanical laboratory this systematic collection begins with
models of bacteria and ends with trees. In other cases, placed in the
adjoining corridor, are representatives, either in alcohol or by means
of models, of most of the orders of flowering plants, as well as a
series illustrating the history of the theory of cross-fertilization,
and the various devices by which it is accomplished; another, showing
the different methods of distribution of seeds and fruits; another,
of parasitic plants; and still another showing the various devices by
means of which plants catch animals.
As an example of the graphic and thorough way in which these
illustrations are worked out, the pines may be cited. There are
fossils; fine specimens of pistillate and staminate flowers in
alcohol; cones; a drawing of the pollen; large models of the flowers;
models of the seeds, showing the embryo and the various stages of
germination; cross and longitudinal sections of the wood; drawings
showing its microscopic structure; pictures of adult trees; and
samples illustrating their economic importance. For the last, the
long-leaved pine of the South is used, and samples are exhibited of
the turpentine, crude and refined; tar and the oil of tar; resin; the
leaves; the same boiled in potash; the same hatcheled into wool; yarn,
bagging and rope made from the wool; and its timber split, sawn, and
dressed.
The series illustrating the fertilization of flowers begins with a
large drawing, adapted by one of the students from Gibson, showing the
gradual evolution of the belief in cross-fertilization from 1682, when
Nehemiah Grew first declared that seed would not set unless pollen
reached the stigma, down to Darwin, who first demonstrated the
advantages of cross-fertilization and showed many of the devices of
plants by which this is accomplished. The special devices are then
illustrated with models and large drawings. First comes the dimorphic
primrose; then follows trimorphic _Lythrum_, to the beautiful model of
which is appended a copy of the letter in which Darwin wrote to Gray
of his discovery:
"But I am almost stark, staring mad over Lythrum.... I
should rather like seed of Mitchella. But, oh, Lythrum!
"Your utterly mad friend,
"C. DARWIN."
Models of the cucumber, showing the process of its formation, and the
unisexual flowers complete this series. Supplementing this are models
and drawings of a large number of flowers, illustrating special
devices by which cross-fertilization is secured, such as the larkspur,
butter and eggs, orchids, iris, salvia, several composites, the
milkweed, and, most interesting of all, the Dutchman's pipe. This is a
flower that entices flies into its curved trumpet and keeps them there
until they become covered with the ripe pollen. Then the hairs wither,
the tube changes its position, the fly is permitted to leave, carrying
the pollen thus acquired to another flower with the same result.
Pictures and small busts of many naturalists adorn both of the rooms.
Of these the most notable is an artist proof of Mercier's beautiful
etching of Darwin. Every available inch of wall space is thus
occupied, or else, in the botanical laboratory, has on it mounted
fungi, lichens, seaweeds, leaf cards, pictures of trees, grasses, and
other botanical objects.
The windows are beautiful with hanging plants from side brackets
meeting the wealth of green on the sill. Here are found in one window
ferns, in another the century plant; in others still, specimens of
economic plants--cinnamon, olive, banana, camphor. On the tables are
magnificent specimens of palms, cycads, dracænas, and aspidistras, and
numerous aquaria filled with various water plants. Most of these
plants are four years old, and all of them are much handsomer than
when they first became the property of the laboratory. How much
intelligent and patient care this means only those who have attempted
to raise plants in city houses can know.
The zoölogical laboratory is quite as beautiful as the botanical, for
it, too, has its plants and pictures. It is perhaps more interesting
because of its living elements. Think of a schoolroom in which are
represented alive types of animals as various as these: amoeba,
vorticella, hydra, worms, muscles, snails and slugs of various kinds,
crayfish, various insects, including a hive of Italian bees, goldfish,
minnows, dace, catfish, sunfish, eels, tadpoles, frogs, newts,
salamanders, snakes, alligators, turtles, pigeons, canaries, mice,
guinea-pigs, rabbits, squirrels, and a monkey! Imagine these living
animals supplemented by models of their related antediluvian forms, or
fossils, by carefully labeled dissections, by preparations and
pictures illustrating their development and mode of life; imagine in
addition to this books, pamphlets, magazines, and teachers further to
put you in touch with this wonderful world about us, and you will then
have some idea of the environment in which it is the great privilege
of our students to live for five hours each week.
In addition to these laboratories there is a lecture room furnished
with an electric lantern. Here each week is given a lecture on general
topics, such as evolution and its problems, connected with the work of
the laboratories.
THE COURSE OF STUDY PURSUED BY THE NORMAL STUDENTS.--Botany: In
general, the plants and the phenomena of the changing seasons are
studied as they occur in Nature. In the fall there are lessons on the
composites and other autumn flowers, on fruits, on the ferns, mosses,
fungi, and other cryptogams. In the winter months the students grow
various seeds at home, carefully drawing and studying every stage in
their development. Meanwhile, in the laboratory, they examine
microscopically and macroscopically the seeds themselves and the
various food supplies stored within. By experimentation they get
general ideas of plant physiology, beginning with the absorption of
water by seeds, the change of the food supply to soluble sugar, the
method of growth, the functions, the histology, and the modifications
of stem, root, and leaves. In the spring they study the buds and
trees, particularly the conifers, and the different orders of
flowering plants.
The particular merit of the work is that it is so planned that each
laboratory lesson compels the students to reason. Having once thus
obtained their information, they are required to drill themselves out
of school hours until the facts become an integral part of their
knowledge.
For the study of fruits, for example, they are given large trays, each
divided into sixteen compartments, plainly labeled with the name of
the seed or fruit within. Then, by means of questions, the students
are made to read for themselves the story which each fruit has to
tell, to compare it with the others, and to deduce from this
comparison certain general laws.
After sufficient laboratory practice of this kind they are required to
read parts of Lubbock's Flower, Fruit, and Leaves, Kerner's Natural
History of Plants, Wallace's Tropical Nature, and Darwinism, etc.
Finally, they are each given a type-written summary of the work, and
after a week's notice are required to pass a written examination.
Zoölogy: The course begins in the fall with a rather thorough study of
the insects, partly because they are then so abundant, and partly
because a knowledge of them is particularly useful to the grade
teacher in the elementary schools.
The locust is studied in detail. Tumblers and aquaria are utilized as
vivaria, so that there is abundant opportunity for the individual
study of living specimens. Freshly killed material is used for
dissection, so that students have no difficulty in making out the
internal anatomy, which is further elucidated with large, home-made
charts, each of which shows a single system, and serves for a text to
teach them the functions of the various organs as worked out by modern
physiologists.
They then study, always with abundant material, the other insects
belonging to the same group. They are given two such insects, a bug,
and two beetles, and required to classify them, giving reasons for so
doing. While this work is going on they have visited the beehive in
small groups, sometimes seeing the queen and the drone, and always
having the opportunity to see the workers pursuing their various
occupations, and the eggs, larvæ, and pupæ in their different states
of development. Beautiful models of the bees and of the comb, together
with dry and alcoholic material, illustrate further this
metamorphosis, by contrast making clearer the exactly opposite
metamorphosis of the locust.
At least one member of each of the other orders of insects is compared
with these two type forms, and, although only important points are
considered at all, yet from one to two hours of laboratory work are
devoted to each specimen. This leisurely method of work is pursued to
give the students the opportunity, at least, to think for themselves.
When the subject is finished they are then given a searching test.
This is never directly on their required reading, but planned to show
to them and to their teachers whether they have really assimilated
what they have seen and studied.
After this the myriapods, the earthworm, and peripatus are studied,
because of their resemblance to the probable ancestors of insects. In
the meantime they have had a dozen or more fully illustrated lectures
on evolution, so that at the close of this series of lessons they are
expected to have gained a knowledge of the methods of studying
insects, whether living or otherwise, a working hypothesis for the
interpretation of facts so obtained, and a knowledge of one order,
which will serve admirably as a basis for comparison in much of their
future work.
They then take up, more briefly, the relatives of the insects, the
spiders and crustaceans, following these with the higher
invertebrates, reaching the fish in April. This, for obvious reasons,
is their last dissection. But with living material, and the beautiful
preparations and stuffed specimens with which the laboratory is
filled, they get a very general idea of the reptiles, birds, and
mammals. This work is of necessity largely done by the students out of
school hours. For example, on a stand on one of the tables are placed
the various birds in season, with accompanying nests containing the
proper quota of eggs. Books and pamphlets relating to the subject are
placed near. Each student is given a syllabus which will enable her to
study these birds intelligently indoors and out, if she wishes to do
so.
In the spring are taken up the orders of animals below the insect, and
for the last lesson a general survey of all the types studied gives
them the relationships of each to the other.
THE COURSE OF STUDY PURSUED IN THE SCHOOL OF PRACTICE.--In addition to
the plants and animals about them, the children study the weather,
keeping a daily record of their observations, and summarizing their
results at the end of the month. In connection with the weather and
plants they study somewhat carefully the soil and, in this connection,
the common rocks and minerals of Philadelphia--gneiss, mica schist,
granite, sandstone, limestones, quartz, mica, and feldspar.
As in the laboratories, so here the effort is made to teach the
children to reason, to read the story told by the individual plant, or
animal, or stone, or wind, or cloud. A special effort is made to teach
them to interpret everyday Nature as it lies around them. For this
reason frequent short excursions into the city streets are made. Those
who smile and think that there is not much of Nature to be found in a
city street are those who have never looked for it. Enough material
for study has been gathered in these excursions to make them a feature
of this work, even more than the longer ones which they take twice a
year into the country.
Last year I made not less than eighty such short excursions, each time
with classes of about thirty-five. They were children of from seven to
fourteen years of age. Without their hats, taking with them
note-books, pencils, and knives, they passed with me to the street.
The passers-by stopped to gaze at us, some with expressions of
amusement, others of astonishment; approval sometimes, quite
frequently the reverse. But I never once saw on the part of the
children a consciousness of the mild sensation that they were
creating. They went for a definite purpose, which was always
accomplished.
The children of the first and second years study nearly the same
objects. Those of the third and fourth years review this general work,
studying more thoroughly some one type. When they enter the fifth
year, they have considerable causal knowledge of the familiar plants
and animals, of the stones, and of the weather. But, what is more
precious to them, they are sufficiently trained to be able to look at
new objects with a truly "seeing eye."
The course of study now requires general ideas of physiology, and, in
consequences, the greater portion of their time for science is devoted
to this subject. I am glad to be able to say, however, that it is not
"School Physiology" which they study, but the guinea-pig and The
Wandering Jew!
In other words, I let them find out for themselves how and what the
guinea-pig eats; how and what he expires and inspires; how and why he
moves. Along with this they study also plant respiration,
transpiration, assimilation, and reproduction, comparing these
processes with those of animals, including themselves.
The children's interest is aroused and their observation stimulated by
the constant presence in the room with them of a mother guinea-pig and
her child. Nevertheless, I have not hesitated to call in outside
materials to help them to understand the work. A series of lessons on
the lime carbonates, therefore, preceded the lessons on respiration;
an elephant's tooth, which I happened to have, helped to explain the
guinea-pig's molars; and a microscope and a frog's leg made real to
them the circulation of the blood.