glass sphere microscope

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A GLASS-SPHERE MICROSCOPEBy Giorgio Carboni, January 1996

Translated by: Sabrina Gemelli, Giacomo Giuli, Karen ColemanAcknowledgments to David W. Walker for his helping in the revision of the English text

CONTENTS

IntroductionThe Leeuwenhoek microscopeFrom Leeuwenhoek's microscope to our modelThe construction of the microscopePreparing the objectiveThe focusing mechanismThe stageThe illuminating systemMounting the objectiveUse of the microscope

MaintenanceTravelling in the microcosm!Pond waterTextile fibers examinationThe cellOnion peelVegetable tissuesBlood smearconclusion

INTRODUCTION

Events happen in nature in many dimensions. Most of them pass unnoticed by observation because their scale is toobig or too small. In fact, we would have to be giants, to follow the path of clouds over continents! And who knowshow big we should be, to be able to contemplate the majestic rotations of our galaxy! On the contrary, if we were assmall as an ant, we could see the amazing miniature world where bizarre creatures like protists live. Themicroscope is an instrument that allows us to leave our dimension and explore the microcosm. A snowfall, a flower,a puddle seem normal things, without surprises. Yet, if you could see the beauty of a snowflake, the hidden shapes

of flowers, the variety and the strangeness of tiny creatures that live in a puddle, you would surely be amazed. Youwill notice that you are surrounded by a fascinating and unknown world. The microscope is the right vehicle toconduct you in this amazing world. Using this instrument you will be able to journey in the microcosm.

-sphere microscope file:///H:/Kinh/K%C3%ADnh%20hi%E1%BB%83n%20vi/htm

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Usually, while attempting to

observe very small objects, we

realize the impossibility of

distinguishing details smaller than

a tenth of millimeter by naked eye.

Hopefully, man created

instruments, like the microscope,

that allowed him to overcome his

natural limits. It is not really

necessary to be a professional to

use a simple but efficient

instrument. As people in the past

did, with passion and patience, we

can try to penetrate into the

microcosm, in search of what

cannot be seen with only our eyes.

The following article contains the

instructions to build a little

microscope. It is an instrument

similar to the one built by Anton

van Leeuwenhoek in the XVIIthcentury, one of the first

microscopes built. Like its

illustrious ancestor, our

microscope is based on a single but

powerful lens.

THE LEEUWENHOEK'S MICROSCOPE

A lot of important scientific discoveries were made by

amateurs. Leeuwenhoek was a simple fabric merchant. In

his job, little "glass pearls" were regularly used to examine

the textiles in detail. None of Leeuwenhoek's colleagues had

the idea of observing anything different to textiles, maybe

because they did not think there was anything else worth

looking at. Leeuwenhoek, however, sparked by a natural

and insatiable curiosity, began to observe everything

around him. He examined saliva and blood, pond water,

vinegar, beer and innumerable other things. Potentially

every subject was good, but pond water or even water from

a simple puddle (the dirtier the better) was the subject of

most interest to examine. He discovered and described

many microorganisms. He sent reports to the prestigious

English Academy of Science, the Royal Society of London,that widely distributed these documents.

Hence the founder of modern microbiology was a mere

amateur, but the scientific community perceived the

importance of his discoveries only after many decades.

Leeuwenhoek's first advance was to move his attention

from textiles to natural objects. To obtain ever-increasing

magnifications, he worked on smaller and smaller lenses,

finally reaching 1-2 mm diameter lenses. Such small and

powerful lenses are difficult to handle and focus. To

overcome these difficulties, Leeuwenhoek fixed them


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between two pierced brass sheets. He arranged the samples

to be observed on the tip of a screw, so that he could

regulate precisely the distance between them and the

objective. The observer had to keep the instrument very

close to his eye and look through the lens.

Essentially this instrument was composed of just one lens. Given the high curvature of its surfaces, this lens wasvery powerful and allowed magnifications of up to 300X, almost one third of the magnification of a moderncompound microscope. In optics, this microscope is defined as simple, because it is formed by just one lens. In the

same period of Leeuwenhoek's studies, the English physicist Robert Hooke had already built a compoundmicroscope, made up of two groups of lenses: objective and eyepiece. However, the fabrication techniques of lenseswere not developed enough and so this kind of instrument had serious optical defects. This rendered it less effectivethan a simple microscope. Only in the first half of the 1800's were compound microscopes perfected. Leeuwenhoekbuilt hundreds of microscopes. Some of these are still exist today and are conserved in museums (fig. 1).Essentially, this instrument was not easy to use and lacked an efficient illumination system.

FROM LEEUWENHOEK'S MICROSCOPE TO OUR MODEL

During the 50's, in the "Scientific American" magazine, D.L. Stong rediscovered the old Leeuwenhoek's microscopeand improved it a great deal. He adapted it to use microscope glass slides and introduced a moveable mirror todirect light through the slides. Another innovation of Stong's is the method of preparing the objective. Leeuwenhoekwas able to produce very little lenses by polishing them manually, using abrasive powders. It seems that he also

obtained these lenses from the bottom of high temperature blown-glass bulbs. Probably, he exploited the surfacetension of the fused glass to obtain high quality spherical droplets. Stong proposed a simpler method to obtain thesespheres. He melted the central part of a glass rod on a Bunsen burner in order to obtain a thin glass wire, then hebrought this wire near the flame to produce little glass spheres of high quality (see figure 4).

Recently in "Scienza & Vita" magazine of December '93, I presented a model of glass-sphere microscope directly

derived from Stong's model, which introduced some other improvements. The first concerns the mechanicalstructure, which was made easier to use, and the second is a new illuminating system. In place of the mirror, withwhich it was very difficult to observe objects clearly, in this new model there is a lamp with a circular diffuser whichmaintains optimal of illumination at all times.

This microscope can reach a magnifications of 200 times or even more, giving surprisingly clear images. Its'construction gives the possibility of enjoying the sensation experienced by scientists three hundred years ago. Themicroscope opens an amazing field of experiments to amateurs, in preparing samples to observe and in the creation

of permanent slides. For teachers this could be an interesting laboratory experience, at the end of which, eachstudent could have a small microscope made with their own hands. In addition, during this experiment, the teacher

would have the opportunity to introduce fundamental concepts in Optics and Biology.

THE CONSTRUCTION OF THE MICROSCOPE


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The microscope I am going to describe can be divided in four parts:-The optical part

-The focusing apparatus-The supporting structure, or stage-The illuminating system

For a better understanding of the construction methods, the reader is advised to refer to figures 2 and 3. You canmodify the project and, if you discover any interesting new solution, tell me and I will examine with interest yourproposals.


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The optical part is formed by the objective. In our case it is a small glass sphere with a diameter comprised between1.2 and 2.5 mm, which works as a magnifying glass. Giving its small dimension, it is very powerful and must bekept at a distance of few tenths of a millimeter from the objects to be observed.


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THE PREPARATION OF THE OBJECTIVE

To fabricate the objective (fig. 4) you need a glass rod with a diameter of 3 to 5 mm, a Bunsen burner and a pair oftweezers. You can obtain these tools for a low price at a chemistry store. For the Bunsen burner, you will need a

small gas tank, a valve, a pressure reducer and a rubber tube. These objects are easy to find in any nearbyhardware store. Using a gas burner of a stove takes a lot of patience and it is not easy to obtain satisfactory results:the flame does not heat the glass enough and there is always the danger of burning your fingers. On the other hand,with the Bunsen burner, you have a concentrated and powerful flame, whose intensity can be regulated. Thisapparatus allows you to work while comfortably seated and this is very important for the fabrication of thesedelicate objectives.

To reduce the formations of bubbles in the glass sphere you created, wash well the glass rod with soap and water,then avoid touching it in the central part. After having lit the Bunsen burner and adjusted the flame, heat the centralpart of the rod while rolling it between your fingers. When the glass is sufficiently soft, remove it from the flame and

pull firmly on both hands until you get a thread of glass with a diameter of 0.3 mm about. With the tweezers breakthe thread in the middle, without touching it with your fingers. Hold one of the thread ends on the side of the flameuntil it begins to melt, forming a little ball. Feed this ball by approaching the thread to the flame until the ballreaches 1.5 to 2 mm of diameter, then remove the thread from the flame and let the ball cool. Now break thethread about 10 mm from the little ball. You will use this tail to glue the objective in its seat. What guarantees thespherical form of the glass ball is the surface tension of the melted glass. However gravitational force tends todeform the sphere, so to obtain objectives of high quality, it is necessary to stay within small dimensions.

You will need to prepare at least a dozen of little glass balls, then with a strong lens, choose one of the correct size


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without air bubbles and other imperfections. This will be the objective of the microscope. The other good objectiveswill be kept in reserve. There will be traces of hydrocarbons on the glass sphere you have just fabricated. The

sphere must be delicately cleaned with a tissue wet with alcohol or saliva. The magnifying power of the objective isgreater the smaller its size. How can you determine the magnifying power? Simply solve the following equation:I=333/d, where I is the magnifying power and d is the diameter of the sphere expressed in mm. For example with asphere of 1,66 mm of diameter you will obtain about a magnification of 200 X.

THE FOCUSING MECHANISM

To focus the microscope you must move the objective near to or further from the sample. For this reason the lens isfixed on a metal blade connected to two screws. The first one should have a bigger pitch and allows quicker but less

precise movements (coarse adjustment). The second one, with a fine pitch allows a more accurate focusing (fineadjustment).

A second metal blade is screwed in, under the slide holding plane and supports the coarse adjustment screw. Thesetwo metal blades, with a thickness of one millimeter, can be of brass or steel. The objective is mounted below theupper metal blade over a hole that we will call the seat. In fig 3 are shown the dimensions for making the seat ofthe objective. The U curve of the two metal blades keeps the screws lined up and this avoids instability of theobjective.As you can see in figures 2 and 3 the objective holder blade is a little curved, otherwise it would slide freely againstthe slide holding plane, and it would move around. To give it stability it is necessary to bend the coarse adjustment

blade slightly up, in this way the objective holder blade bends elastically and stabilizes itself. Complete theseoperations before mounting the objective, to avoid running the risk of detaching and damaging it. The tip of the

micrometric screw must be smoothed to avoid scratching the slide holding plane.

THE STAGE

The construction of the supporting structure, or stage, is particularly simple. It is necessary to construct a little boxopen on two sides. For the base and the two walls you can use wooden boards fasten with nails and glue. For theupper part, where you laid the glass slides, and where the fine focusing screw slides, it is necessary to use a smooth

yet hard material for example Formica. On this plane, it is necessary to make a hole of about 10 mm in diameter topermit the passage of the light of the illuminator. You must also make two holes for the screws which hold thecoarse adjustment blade. On one of the two lateral walls of the stage you must make a groove to set the blade. The

slide holding plane must be fixed to the base with screws so that it can be removed.

THE ILLUMINATING SYSTEM

Besides the objective, the illuminating system is the most critical part of the instrument. If it is well adjusted, itallows objects to be seen with an amazing sharpness for an instrument so simple, otherwise stripes of light will

confuse every detail. It is important that the light source has a circular form, a uniform brightness and an adequatedimension. The sun is not a good source. It is too strong and its emitting surface is too small. Using sunlight, theobjects appear as clusters of extremely contrasty granules without details. I have tried to use a swinging mirror to

collect the light coming from different sources (lamps or windows), according to the aforementioned suggestions ofStong. It is a simple solution, but the adjustment of the mirror is very critical and, moreover, if you move themicroscope you will lose the adjustment you have reached. If you collect the light of a neon lamp, due to itslengthened form, the objects you observe will be distinct only in one direction. For similar reasons it is necessary toexclude the use of naked filament lamps.

A very effective and easy solution is a little box containing an electric torch lamp, fed with a flat battery (4.5 V). This

solution always gives better lighting conditions and avoids the problems due to the mirror adjustment. You can alsogive the microscope to another observer without losing the illumination adjustment. The battery can be fixed to thewall of the box by a rubber band. As everyone knows, batteries are spiteful, they exhaust just when you need them!

In example, when you want show the microscope to some friend. So, besides the battery, it is better to install aconnector to supply energy from an low voltage electric power supply. When the power supply is used, the batterymust be disconnected.

The illuminating box can be obtained from a container for 35mm film (24 mm x 36 mm), cutting it in half (to retainthe cover, smooth the edge by melting it slightly over a flame). Set up the lamp in the proper lamp-holder insertedin a lateral hole on the box. To increase the efficiency of the illuminator, coat the inside of the box with white paper,or better, with light green paper to raise the color temperature of light. Fix the box to the stage with a screw. Thelight should pass through a circular opening made on the cover, with a diameter of 8 mm. You must screen theopening with an translucent plastic disk so that the filament will be hidden and there will be a uniformly illuminated


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circular disc. This screen should not be so transparent either to let the filament be seen, nor so opaque as to absorbtoo much light. Observing figure 3, notice how the light source, the hole on the slide holding plane, the sample

slides, the conical seat with the objective and the eye are all on the same vertical axis.

MOUNTING THE OBJECTIVE

The objective has to be glued under the

focusing metal blade in the conical seat (fig.

3). Before doing this, it is necessary topaint opaque black the objective seat and a

part of the blade all around. This reduces

reflections and interference from light and it

must be done on both faces of the blade.

This operation can be done easily by a

spray-can, but it is also possible to paint

with a brush.

To glue the objective, place a drop of

nail-polish only on the glass thread that the

sphere is connected to (fig. 5). Without

touching it with your fingers, the objective

must be pressed a little bit against the seat,

to eliminate any possible gaps. In fact, if

some light should pass between the lenses

and the seat, the contrast of the image

would be considerably reduced.

USE OF THE MICROSCOPE

This instrument is suitable for

observing transparent

objects. For this reason it is

better to choose very small

objects which are transparentand thin. You must put the

sample over a glass slide.

With a dropper, drip two

drops of water on the sample.

Then cover this with a

coverslip (fig. 6). When you

place the slide under the

objective, be careful neither

to knock it nor to wet it with

water. This lens should be

only a few tenths of a

millimeter away from thecoverslip.


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Switch on the illuminator.

Center the sample by observing

the light variation through the

objective. Now bring your eye

as close as possible to the

objective. You will see the

observation field widen (at the

beginning it is a problem to find

a place for your nose!). Now

move the focusing screws to

make the image distinct.

Moving the objective holder

blade and the slide (fig. 7) you

can easily explore the

observation field.

MAINTENANCE

Never touch the objective with your fingers and, if it is necessary clean it, gently use a wet cotton-bud. While doingthis, hold the objective underneath to avoid breaking the thin glass thread to which it is attached. After use, store

the microscope and all its' accessories in a closed box.

TRAVELING IN THE MICROCOSM!

Required materials: the microscope, a box of glass slides and a box of coverslips, a dropper or a pipette, tweezerswith a thin end. These materials can be obtained from chemical and laboratory product shops, usually found nearuniversities.

POND WATER


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The cells of corn and those of pith elder are

dead. If you want to observe live cells, take

an onion. Cut it into slices and then take a

scale. Try to raise the peel that covers the

onion scale with tweezers. Draw out a

cutting and put it on a slide, add two drops

of water and cover. This epithelial tissue is

made of a single layer of cells. This is

important because it allows us to see the

cells without making any difficult thin

sections. Through the microscope the tissue

looks like a tiled floor (fig. 10). While

isolated, cells usually have a spheroidal

form, when they are tightly packed one next

to the other in a tissue, they take a

polygonal form, like soap bubbles and metal

crystals.

While observing the onion cells, you can distinguish a cellular wall and a little spheroidal form, the nucleus. Thenucleus contains the DNA, the "plan" of the whole onion. If you have methyl blue (you can buy it in a shop of

chemical products), prepare a 0.5 % solution in distilled water (you can find this in a pharmacy). Take a peel of afresh onion or one has been standing in water for a few days, thus biologically active. Dip the peel in the dyingsolution. The methyl blue will color the nucleus in the cells with a deep blue. If the cells are still alive you will be ableto see one or two spherical features of a darker color in the nucleus. These are the nucleolus. This is the place whereribosomes are produced. They are organelles destined to the synthesis of proteins.

VEGETABLE TISSUES

A leaf is too thick to be directly observed by the

microscope. It is necessary to obtain a thin cross

section. The problem is that the leaf bends when you

try to cut it. To solve this problem, take a piece of

elder pith (you can extract it from a dry branch of thatplant), longitudinally cut it and put the leaf inside it,

like in a sandwich. With a new razor blade you can

now cut thin slices of the leaf without it bending

(fig.11). At the place of the elder pith you can use a

carrot, or some styrofoam provided it is homogenous

and not made up of an agglomerate of little spheres.

With some practice you will be able to cut slices with

the thickness of about one cell. In the upper part of a

leaf section, you can distinguish a cell-layer lined up

in a kind of palisade. In the lower part, you can see a

spongy tissue in which the gaseous exchanges take

place and, on the epidermis, small openings calledstomas. Inside these cells you can see chloroplasts

which are organelles where photosynthesis takes

place. Here carbon dioxide and water are transformed

by the energy of the Sun into sugars and, as a waste

product, oxygen.


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In a similar way you can prepare and

observe other vegetable tissues, for

example the stem of herbaceous plants. The

section of a violet petal shows epidermal

finger-like cells (fig.12). Inside these cells

you can see the chromoplasts, organelles

which contain the pigments coloring petals.

BLOOD SMEAR

If you want to see blood red cells

(erythrocytes) you have to prepare a blood

smear. With a sterilized needle prick a

finger-tip. Put a drop of blood on a slide. It isimportant that the quantity of blood is not

excessive, otherwise the red cells could hide

the leukocytes. In fact, to make a smear, it is

enough to leave a spot of blood of 3 mm

about in diameter on the slide. As shown in

figure 13, keep the coverslip tilted and bring

it near the drop of blood until it touches the

slide and adheres to the drop itself. Move the

coverslip so as to distribute the blood on the

slide underneath. You can observe this slide

without adding water and without covering it.

CONCLUSION

The microcosm is extraordinarily rich with marvels. Strange inhabitants live in unexpected places. Buy some bookabout using microscopes, they will help you in your search for Vorticella, Rotifera, Diatoms, Paramecia and Amoeba.Who knows, perhaps you could meet a Hydra, a curious being similar to an octopus, colored green because many ofits cells possess chloroplasts and carry out photosynthesis. As soon as you say: "What a strange plant!", it willcapture a prey with one of its stinging tentacles and ingest it. And maybe you will see it moving doing cut capers oras a caliper "So it is an animal!" The Hydra does not care about this problem it is entirely our own, it settles down onthe bottom and stretches its green tentacles at the sun.

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