INTRODUCTION
With relation to the senses,
Maria Montessori has extended the number of senses from five
to seven. To the senses of smell, taste, sight, hearing and touch,
she added the stereognostic sense, (the knowledge of 3dimensionality)
and the basic sense (the sense of mass, that is, of heaviness
or lightness). The visual and stereognostic senses are directly
related to the following work in geometry.
Maria Montessori has also identified three different aspects
of education of the visual sense: according to size, form and
color. In geometry we will deal with visual education according
to size and form, thus eliminating color. If the child did not
have previous Children's House training, this visual education
must be offered differently, because it is really only pertinent
to a younger age.
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PLANE INSETS
Materials:
...Geometry cabinet
...Additional insets, including pictures of the figures
...2 of the 3 boxes of pictures of the figures:
...entire figure "surface" shaded; the fine "contour"
margin of the figure
...Reading labels
...box of command cards
Description of Materials:
geometry cabinet The presentation of this material follows the
order in which the drawers are arranged. Since the presentations
differ from Children's House to the elementary school, so the
order of the drawers and the arrangement of the contents of each
drawer differs from Children's House to the Elementary school.
Order:
Presentation tray  0 comes first at both levels.
The names of the drawers in the Children's House and their order
is:
1 circles; 2  rectangles; 3  triangles; 4  polygons; and
5  different figures.
At the elementary level the
names and order are:
1  triangles; 2  rectangles;
3  regular polygons; 4  circles; and 5  other figures.
At the Children's House level,
the children worked directly for the education of the visual
sense, and only indirectly to learn the geometric figures. In
the elementary school what was a sensorial exploration becomes
a linguistic exploration via etymology. What was an indirect
approach to geometry becomes an actual study of geometry.
Therefore in elementary the drawer of triangles comes first because
the triangle is the first polygon we can construct in reality,
having the least number of sides. The second drawer logically
follows as the quadrilaterals, specifically rectangles. Regular
polygons follow beginning with the fivesided figure progressing
to ten sides. circles follow, because a circle is the limit of
a regular polygon having an infinite number of sides.
From Children's House to elementary the order has changed: from
easiest to most difficult, to: from threes sides to an infinite
number of sides. This correlates with the change from seeing,
touching, and naming to a focus on etymology and reasoning.
Arrangement:
The presentation tray contains the three fundamental figures
of geometry, that is the only regular figures. The equilateral
triangle is the only regular triangle. The square is the only
regular quadrilateral. The circle is the limit of all regular
polygons having an infinite number of sides. the triangle is
"the constructor of reality". For every plane figure
can be decomposed into triangles, just as all solids can be decomposed
into tetrahedrons. The square is the "measurer of surfaces"
just as the cube is the measurer of solids. The circle is the
measurer of angles. In Children's House. In the Children's House
the arrangement is square (left), circle (top), triangle (right).
In elementary the arrangement is triangle (left), square (top),
circle (right).
The triangle tray examines triangles according to their sides
on top; the bottom three examine triangles according to their
angles, at both levels. In the Children's House the order is
(top  from left to right): equilateral, isosceles, scalene (bottom
 from left to right), acuteangled, rightangled, obtuseangled.
In elementary (top  from left to right): scalene, isosceles,
equilateral (bottom  from left to right), rightangled, obtuseangled,
acute angled.
In the rectangle tray, the base of the smallest figure is 5 cm.
which is 1/2 the base of the largest which is a square. In Children's
House the order is largest to smallest, elementary the reverse.
The regular polygon tray is ordered identically at both levels,
progressing from five to ten sides. It is understood that these
are the regular polygons having more than four sides, since the
equilateral triangle and the square (first tray) are also regular
polygons.
In the circle tray, the diameter of the smallest is 5 cm.; the
diameter of the largest is 10 cm. It is ordered from largest
to smallest in the Children's House and the reverse in elementary.
The arrangement in the other figure drawer is the same for both
levels: trapezoid, rhombus, quatrefoil, oval, ellipse, and curvilinear
triangle (Reuleaux triangle).
Additional insets for the geometry cabinet:
Two triangles: acuteangled
scalene triangle, obtuseangled scalene triangle
Eight quadrilaterals:
common quadrilateral (four different sides and four different
angles)
common parallelogram (opposite sides are parallel and equal)
four trapezoids
equilateral trapezoid
(constructed from three equilateral triangles)
scalene trapezoid
rightangled trapezoid
obtuseangle trapezoid (two obtuse angles opposite)
Two deltoids or kites: one with unequal diagonals
one with equal diagonals
Two quatrefoils: quadrilobed
epicycloid
Including surface cards for
each.
Note: Ten dominates all of the plane insets:
Presentation tray: triangle sides  10cm.; square sides  10
cm.; circle diameter  10 cm.
Triangles: Hypotenuse of the obtuseangled triangle  10 cm.
Rectangles: Height of each  10 cm.
Regular polygons: All can be inscribed in a 10 cm. diameter circle
Circles: Diameter of largest  10 cm.
Other figures: Trapezoid base, short diagonal in rhombus, distance
between opposite lobes in quatrefoil, distance between two opposite
cusps in oval and ellipse, base of triangle used to construct
curvilinear triangle, all  10 cm.
Extra figures: Triangles, diagonal of parallelogram, equilateral
trapezoid base all 10 cm.
Distance between points on adjacent lobes of quadrilobed quatrefoil,
and between opposite lobes of epicycloid  10 cm.
No 10 cm. exists in the common quadrilateral, deltoids and the
last three trapezoids.
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THE GEOMETRY CABINET
Introduction:
In this second presentation of the geometry cabinet (first being
in CH) the visual memory is aided by etymology, and no longer
by the tactile sense. therefore the emphasis on that element
is eliminated. Instead the emphasis is placed on etymology 
the heart of our language.
Presentation tray
Materials:
...Appropriate drawer
...Three reading labels  "triangle", "square/quadrangle",
and "circle"
Presentation: With only the tray on the table,
the teacher takes out the triangle and identifies it.. this is
a triangle. The child is asked to identify the angles and count
them (triangle: Latin tres, tria  three and angulus
 an angle; thus triangulum  triangle). Triangle means
three angles. Place the inset in its frame in the drawer.
The teacher isolates the square and identifies it (square: Old
French esquarre, esquerre <Latin ex  out, and
squadra  square; thus to make square>). It is such
an old word that the etymology doesn't help us as much. Put the
square back. Isolate the circle and identify it (circle: Latin
circulus  a diminutive of circus  a circle).
Again the etymology doesn't help us because this shape has been
called a circle as far back in time as we know.
As all three inset are placed on the table, review the first
period. Rearrange the order and continue with the second and
third periods. Invite the child to place the insets in their
frames.
Exercise: Give the child the reading labels
to place on the insets in their frames: triangle, circle, square/quadrangle.
Note: The word quadrangle is not used at this point.
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TRIANGLES
Materials: Reading labels  "scalene triangle",
"isosceles triangle", "equilateral triangle",
"rightangled triangle", "obtuse angled triangle",
"acuteangled triangle"
Presentation: Take out the
first triangle in the first row. Invite the child to identify
the three sides and observe whether the sides are alike or different.
all three sides are different, this is a scalene triangle. Relate
the story of the farmer and the ladder he used to pick fruit
from his trees. Unlike the ladders we use today, the rungs of
this ladder were all different lengths. These ladders are still
used today in lesser developed countries. Just as all the rungs
are different lengths, the sides of this triangle are all different
lengths (scalene: Latin scala, usually plural scalae
 ladder, flight of steps or Greek: skalenas  limping,
uneven).
Isolate the second triangle in the first row. Invite the child
to carefully observe its sides  two are alike. This is an isosceles
triangle (isosceles: Greek isos  equal, and sceles
 legs; thus having equal legs). Here it means two equal legs,
or sides.
Isolate the third triangle. By observing and turning the inset
in its frame, the child sees that all of the sides are the same.
This is an equilateral triangle (equilateral: Latin aequus
 equal, and latus, lateris  a side; thus having
equal sides). Place the three insets on the table and do a three
period lesson.
Isolate the first triangle in the second row. Identify the right
angle. This is a right angle, it is erect. This is a rightangled
triangle. How many right angles does it have? Only one.
Isolate the second triangle. Identify the obtuse angle. Obtuse
means dull. This is an obtuseangled triangle. Count the obtuse
angles... only one.
Isolate the third triangle. All of these angles are smaller than
the right angle. They are acute angles. Acute means sharp, pointed.
(feel how it is sharper than the right or obtuse angles). This
is an acuteangled triangle. How many acute angles does it have?
Three.
Bring out the three triangles and review the first period. The
triangle must have one right angle to be a rightangled triangle...
and so on. Second and third periods follow. Give the child the
reading labels.
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RECTANGLES
Materials: Reading labels: five "rectangle"
and one "rectangle/square"
Presentation: Isolate the first inset. Identify
it and give etymology (rectangle: Latin rectus right,
and angulus  an angle; thus having all right angles.
Invite the child to identify the other rectangles as they are
isolated.
Isolate the last inset. This is also a rectangles because it
has all right angles, but it is also a square. Do a three period
lesson and give the child the reading labels.
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REGULAR POLYGONS
Materials: Reading labels: "pentagon", "hexagon",
"octagon", "nonagon", "decagon",
and a series of ten cards: "</angulus", "3/tria",
"4/quatuor", "5/pente", "6/hex",
"7/hepta", "8/okto", "9/nonus or ennea",
"10/deca", "n/polys"
Drawer 3 and the frame and inset of triangle and square from
the presentation tray.
Presentation: Position the two extra insets to
the left of the drawer in line with the top row. Isolate the
triangle. Invite the child to identify an angle. Identify one
on the square also. Isolate the decagon and invite the child
to identify an angle. Feel it and compare it to the triangle
and square. This angle is less sharp than the angles f the triangle.
Present the symbol card which represents angle (<). Identify
the angles on the triangle and count them. Place the 3 card and
the angle card side by side over the inset frame. Continue with
each of the other figures, counting the angles, and placing the
corresponding numeral card with the angle card. Since there is
only one angle card, it floats from one inset to the next as
needed.
Isolate the triangle inset and the two cards 3 <. The child
identifies the figure and gives the meaning of its name. Then
turn over the cards reading the Latin words which were made into
a compound word to get triangle. Return the inset to its frame
with its number card.
Isolate the square inset and cards: 4 <. Turn over the cards
to find that 4 angles was quatuor angulus, from which our word
quadrangle was derived.
Go on naming the other figures in this way using the Greek word
for angle  gonia. Note: nonus  ninth, and ennea
 nine.
After ten we have no more figures in our materials. Imagine a
figure with any number of sides... 15, 20, 100, any figure with
more than three sides. We can indicate this number by n. Bring
out the card and place next to it the angle sign. turn over the
cards: polys  many, and gonia  angle. Any figure that has more
than three sides is a polygon. All of these figures we've examined
up to now are polygons.
Beginning with the triangle turn all of the figures in their
frames to show that the sides and angles are equal. All of these
are "regular polygons". Name each figure: regular triangle
is an equilateral triangle; a regular quadrangle is a square;
a regular pentagon; a regular hexagon... and so on. Do a threeperiod
lesson and give the reading labels.
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CIRCLES
Materials: Reading labels: 4 "circle",
1 "circle (smallest)", 1 "circle (largest)"
Presentation: The child identifies all as circles
and puts out the reading labels.
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OTHER FIGURES
Materials: Reading labels: "trapezoid",
"rhombus", "quatrefoil", "oval",
"ellipse", "curvilinear triangle" or "Reuleaux
triangle"
Frame of the circle inset (for presentation of ellipse)
Presentation: Isolate the trapezoid and identify it (trapezoid:
Greek: trapezion  a little table). In order to understand
why this figure has its name we must go back in time to see what
a table of the Greeks looked like. Nowadays our tables don't
look trapezoidal. Some Spanish tables have two legs but still
not trapezoidal. The Greek table was like a Spanish table because
it had two legs, yet it was more stable because the legs were
inclined.
Isolate the rhombus and identify it. This is a rhombus (rhombus:
Greek: rhombos  magic wheel, top) In ancient Greece,
in the city of Athens, during a religious procession through
the streets, a priest walked along with a cane (rod) raised over
his head. At the end of the cane there was a cord attached, and
at the end of the cord there was a rhombusshaped figure attached.
He rotated the cane in the air as he walked causing this figure
to spin around like a top, making a characteristic sound. This
was part of a religious ritual.
Isolate the quatrefoil and identify it (quatrefoil: Old French
quatre  four, and foil  leaf). This figure has
the shape of a fourleaf clover, considered a sign of good luck.
Isolate the oval and identify it (oval: French ovale <Latin
ovum>  egg). This figure has the shape of an egg.
Isolate the ellipse and identify it (ellipse: Greek elleipsis
 an omission or defect <elleipo  to leave out>).
What has been left out? Think of the ideal figure, the circle.
Place the inset of the ellipse in the circle frame and it is
easy to what is missing. This is also the shape of the path that
the earth follows around the sun.
Isolate the Reuleaux triangle and identify it (curvilinear: Latin
curvus  curved, and linear  a line). This triangle
has three sides which are curved lines. It is named after a man
name Reuleaux who discovered the properties of this shape. He
found that a drill bit made in this shape will make square holes.
Give threeperiod lesson and give the reading labels.
Age: 6 years and on
Aim: Knowledge of the geometric figures and their
relative exact nomenclature.
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Note: The triangle,
the smallest figure in reality is the constructor of all other
figures in reality. The tetrahedron, the smallest solid in reality
constructs all of the other solids in space.
Materials:
Box 1
Two yellow equilateral triangles
Two yellow, two green rightangled isosceles triangles
Two yellow, two green, two gray rightangled scalene triangles
One red smaller rightangled scalene triangle
On red obtuseangled scalene triangle
(Each triangle has a black line along one side)
Box 2 
Two blue equilateral triangles
Two blue rightangled isosceles triangles
Two blue rightangled scalene triangles
One blue obtuseangled scalene triangle
One blue rightangled scalene triangle (corresponds to the red
triangle from Box 1)
Box 3 
Twelve blue rightangled scalene triangles with no black lines.
The angles measure 30, 60, and 90 degrees.
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FIRST BOX
Presentation: Invite the child to remove the triangles
from the box, and then sort the triangles according to shape.
Having done this, ask the child to separate each pile according
to color, resulting in various piles of triangles having both
shape and color in common. Isolate the two red ones to be used
later.
The teacher takes the pile of two equilaterals and separates
them in such a way that the two black lines are facing each other.
Watch, these black lines are like a magnet. Slide the two triangles
together so that the black lines meet. Invite the child to do
the same, leaving the joined triangles in place.
Identify the figures that have been constructed: a yellow rhombus,
a green square, and a gray rectangle. The teacher identifies
the other three figures as common parallelograms (parallelogram:
Greek parallelogramium <parallelos, parallel,
and grame, figure>). therefore a parallelogram is a
plane figure having parallel sides. By simultaneously running
two fingers along two parallel sides, the teacher gives a sensorial
impression of parallel. We also call them common parallelograms
to differentiate them from the square, rectangle, and rhombus
which could also be considered parallelograms. The child names
each figure as they are indicated by the teacher.
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SECOND BOX  CONSTRUCTION OF QUADRILATERALS
Presentation: Invite the child to sort the triangles
by shape. As before, set aside the two small triangles which
correspond to the red ones of the first box.
Isolate the two equilateral triangles and invite the child to
form all of the possible quadrilaterals. try as he might, he
can only form one. The child identifies it as the rhombus.
Leaving the rhombus intact, the teacher takes the two rightangled
isosceles triangles and forms the possible figures. The child
identifies the figures as they are made. there are two: the square
and the common parallelogram.
The child may see two different parallelograms. Trace one on
a sheet of paper. Form the other and superimpose it. The second
parallelogram doesn't fit inside the contours of the first. Trace
the second parallelogram and cut out the two figures. By placing
the cutouts back to back, we can see that one is the mirror
image of he other, therefore they are the same parallelogram.
The child is invited to form the possible quadrilaterals with
the two rightangled scalene triangles. The child identifies
the three:
rectangle, common parallelogram, a different parallelogram.
One by one, isolate each type of triangle, ask the child to classify
the triangle according to its sides, and ask, "Of how many
different lengths are the sides of this triangle"? Conclude
that with a triangle whose sides have all one measure, we can
form only one figure  the rhombus. With a triangle whose sides
have two different measures, we can form to figures  square
and common parallelogram. With a triangle whose sides have three
different measures, we can form three figures  rectangle and
two parallelograms.
Direct Aim: To give the relationship between
the number of different lengths of the sides and the number of
figures which can be possibly constructed.
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SECOND BOX  HEADS & TAILS
Presentation: Every plane figure, like a coin,
has two sides. One side is called obverse or heads; it is the
side which has a face or the principle design. When you turn
it over, you have the reverse side or tails. All of these figures
have an obverse (blue) and a reverse (natural wood or white)
side.
Isolate the two equilateral triangles. Invite the child to form
as many figures as possible. As before, he can make only one.
Suggest that he tries with one obverse and one reverse side.
It won't help. There is only one figure he can make.
With the two isosceles triangles he makes the two possible quadrilaterals
with the obverse sides. Invite the child to make a triangle.
The child classifies the triangle: isosceles. By turning one
triangle to its reverse side, the child can make no new figures.
With the two scalene triangles, the child tries to form all possible
quadrilaterals first with the two obverse sides (yielding the
same three figures as before) and then with one reverse side.
The child is able to form a new figure: a kite (or a deltoid,
having the form of the Greek capital letter Delta ).
Invite the child to make triangles, first with obverse sides
(yielding none) and then with one reverse side. The child classifies
the triangles he makes: acuteangled isosceles and obtuseangled
isosceles triangles.
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TRAPEZOID
Presentation: With the two small red triangles,
invite the child to unite the triangles along the black lines
and identify the figure obtained  a trapezoid.
Using the two corresponding blue triangles, invite the child
to form the figure which he already knows and to identify it
 a trapezoid. Continue making other quadrilaterals using only
the obverse sides. The teacher identifies the figure obtained.
since it has four sides we can call it a quadrilateral. It is
a concave quadrilateral  a boomerang (it may also be called
a reentrant).
Invite the child to turn over one triangle to form any other
figures, quadrilaterals or triangles. The quadrilateral is called
a common quadrilateral. The triangle is an obtuseangled isosceles
triangle. (Note: This triangle has great importance in the later
study of the area of a trapezoid.) Recall the figures formed
by these triangles; there are four.
Age: After 6 years
Aim: Exploration of the triangle as the constructor
of triangles and quadrilaterals.
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THIRD BOX
Presentation: Isolate one triangle. Ask the child
to identify each of the angles, and the biggest and smallest
angles. This angle which is neither smallest nor biggest we can
call the medium angle. The child names each angle: smallest angle,
medium angle, biggest angle.
First star: Let's unite all the triangles by their smallest angle.
The teacher positions a few and allows the child to continue.
How many points does this star have? Twelve. with all of the
triangles at our disposal, we can make only one star with twelve
points.
Second star: Let's unite all the triangles by the medium angles.
How many points does this star have? Six. Try to make another
star with the triangles that are left. With all the triangles
at our disposal, we can make two stars with six points.
Third star: Let's unite all of the triangles by the largest angle.
How many points does this star have? Four. This symbol is very
famous; it is the star of Saint Brigid, the patron saint of Ireland.
Try to make another star like this. With all the triangles at
our disposal, we can make three stars with four points.
Aim: Use of the triangle as a constructor to indirectly
demonstrate the following:
30o x 12 triangles = 360o 60o x 6 triangles = 360o 90o x 4 =
360o
360o / 30o = 12 tris. 360o / 60o = 6 tris. 360o / 90o = 4 tris.
360o / 12 triangles 360o / 6 = 60o 360o / 4 = 90o
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Related activities:
1. Construct the first star.
Notice that the triangles meet at a point in the center. We must
divide this star into two equal parts, leaving six triangles
on one side and six on the other. Many possibilities exist; simply
choose on and slide the triangles away to leave a gap.
We want to make the point at the top of one side meet the point
on the top of the other. Slide one half along and then towards
the other to make the two points meet at the top. We see that
they have met at the bottom also, and where there was a point
in the center there is now a line segment.
Again divide the figure in half, this time along the other side
of the triangle which was displaced before. Separate the two
halves to leave a gap. Identify the two points at the top and
bottom which should meet. Slide one half into position. We see
that a quadrilateral (a rhombus) has been created at the center.
Continue in the same manner, identifying the figure formed at
the center each time: equilateral hexagon, equilateral octagon,
equilateral decagon, equilateral and equiangular, therefore regular
dodecagon. This is the first diaphragm. It is like the diaphragm
of a camera. Bring one in to demonstrate.
2. Construct the second star.
As before, divide into two equal parts. Slide one side so that
the vertices of the extreme angles meet. Note the change from
a point to a line segment. Continue naming each of the figures
made, ending with the equilateral and equiangular, therefore
 regular hexagon.
3. Construct the third star.
Divide as before and slide one half. In this only the point,
line segment and square are formed in the center. This is the
third diaphragm.
Note: This third diaphragm
will serve as a point of reference for two algebraic demonstrations
of the Pythagorean theorem.
4. The children draw, cut,
and paste the stars and diaphragms.
5. Older children may solve
for the areas of the diaphragms and their internal figures, and
find the relationship between them.
6. Constructing the second
or third star, the child forms other figures by fitting in the
angles.
7. Encourage further explorations
using these triangles.
Direct Aim: Exploration of shapes using triangles.
Indirect Aim: Preparation for the sum of exterior
and interior angles.
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