Would it be possible to make a microscope on the island using just a basic array of wire, glassware, kitchen utensils and a car battery but not a clean glass lens in sight? Copyrighted imageCredit: Used with permission

How does a microscope work?

Essentially, a microscope is just a lens. You can see the principle quite easily by looking through a tiny drop of water. Try balancing a water droplet on a 2mm hole made in cardboard and looking through it. You'll have to get your eye very close - and the object you're looking at very close too - but it magnifies surprisingly well.

Why does glass work better than water at magnifying things?

Glass has a larger refractive index than water, so light travelling through a sphere of glass is bent much more than when light travels through a sphere of water of the same size. So it can magnify it better.

Why use a sphere?

A sphere has a highly curved surface, which makes for a very powerful lens. The diameter of the sphere determines the magnification - the smaller the diameter, the greater the magnification.

Copyrighted imageCredit: Used with permission

Who invented the microscope?

Strong lenses were used since antiquity to examine tiny objects. One of the earliest uses of a simple microscope was by Antony van Leeuwenhoek (1632-1723) in around 1680.

Leeuwenhoek was a Dutch fabric merchant who used little "glass pearls" to examine the textiles in detail. Leeuwenhoek began to observe everything around him from saliva to pond water to beer. He discovered many micro-organisms and was the first person to describe bacteria, blood cells and sperm cells.

To obtain ever-increasing magnifications, Leeuwenhoek worked on smaller and smaller lenses, finally reaching 1-2 mm diameter lenses. Such small and powerful lenses are difficult to handle and focus: you have to keep the instrument very close to your eye and look directly through the tiny lens.

Would it be possible to make a simple microscope on the island?

Despite the fact that there were no clean, unscratched lenses on the island, there is a very simple microscope you can make using a tiny, ~2mm diameter ball of glass. To get lenses of high quality, the spherical balls need to stay small.

Copyrighted imageCredit: Used with permission

The reason why the glass beads are spherical instead of tear-drop shaped is due to surface tension. With small enough blobs of melted glass, the force of surface tension keeps the balls round. Once the balls get too big, gravity starts to deform the spheres into drop shapes.

WARNING: It is essential that you wear eye protection when using a flame and working with glass.

• We heated the central part of the glass rod until it looked like it had softened.
• We removed it from the flame and pulled it firmly apart until it was very thin.
• We broke the thread using tweezers.
• We held one of the threads horizontally in the flame until it began to melt, forming a little ball.
• We rotated the thread in the flame until the ball reached 1.5 to 2mm in diameter.
• We then removed the thread from the flame and let the ball cool. When cool, we broke off the thread about 10mm from the little ball using the tweezers. We used the tail to glue the lens in its seat.
• It took us a few tries to get a glass bulb without air bubbles or other imperfections.

How can we determine the magnifying power?

Copyrighted imageCredit: Used with permission The smaller the size of the sphere, the greater its magnifying power.

This equation is used: I = 333/d where I is the magnifying power and d is the diameter of the sphere in mm.

Therefore, we can work out the magnification of these spheres:

A sphere of 1.66mm in diameter = 200X

A sphere of 3.33mm in diameter = 100X

A sphere of 1.11mm in diameter = 300X

How do we view objects through the glass bead?

As the bead is so small it needs to be put inside housing apparatus: on the island, we used a saucepan and a wooden base. A mirror was used to shine light onto the sample to illuminate it.

Since the sphere can only focus at a short distance the objects we examined had to be thin. We put the samples - such as onion cells or human hair - onto a piece of glass and held them in position with a couple of drops of water.

Copyrighted imageCredit: Used with permission

Copyrighted imageCredit: Used with permission We used water and a cover slip and put the sample under the lens so that it was almost touching.

We incorporated an adjustment mechanism to focus the microscope.

We proved that it's possible to create a microscope with 200X magnification from just a glass rod, a saucepan and a spirit burner!

 

 

Kathy and her microscope

Web Links

The BBC and the Open University are not responsible for the content of external websites.

Water Microscopes - by Mike Dingley, Australia on the Microscopy UK website

Microscopy UK - the home of Popular Microscopy on the Web

A Glass-Sphere Microscope - the Fun Science Gallery site

Anthony van Leeuwenhoek - from the University of California Museum of Paleontology site

Cell Diversity - from the Biology 150 Laboratory Review, University of North Dakota site

Use of Microscopes and Creation of Slides - from the Michigan Tech Mathematical Sciences site

Books

Advanced Physics by Tom Duncan, John Murray