The Instant Microscope: Just add water

Mark Valentine, Electrical Engineer

After doing some research into the origins of microscopy, I was quite surprised to learn about the number of early contributors to this field. I had once assumed that Leeuwenhoek invented the microscope, but this is not true. The essence of his achievement lies in his inspiration to improve the microscope as an instrument for studying nature.

Just as Galeleo did not invent the telescope, but was the first to turn one of significant strength towards the heavens, Leeuwenhoek was the first person to place specimens from nature under a powerful microscope. One characteristic that both men seem to have shared was a determination to improve the performance of their optical instruments. Perhaps both men were motivated by a deep awareness of what nature would reveal in exchange for only an order of magnitude of increased magnification.

It paid off. Galileo was the first to see the four largest moons orbiting Jupiter, now collectively named in his honor. Leeuwenhoek, perhaps treated to the greater spectacle, was the first to see the amazing diversity of single-cell organisms.

Alvaro Amaro de Azevedo has written an excellent article for The Citizen Scientist on “The challenge of Grinding a Miniature Biconvex Lens.” This article describes how to make powerful lenses for use in microscopes having a similar design to Leeuwenhoek's. These are, in essence, extremely powerful magnifying glasses.

While reading about the history of single-lens microscopes, I came across an interesting design called the water drop microscope. In these instruments, a single drop of water suspended beneath the perimeter of a small hole forms the lens.

Using a soda straw and a plastic lid from a microwave meal that had four small vent holes (each about 4.5 mm in diameter), I was able to make a crude water drop microscope on a kitchen countertop. I used the straw as a water dropper to place differently sized water drops in each of the holes in the lid. As in the early water drop microscopes, each drop was suspended beneath its respective hole. The drops of water were kept from touching the countertop by a lip around the lid. The lid was then positioned so that one drop extended beyond the edge of the kitchen countertop, as shown in Fig. 1.

Figure 1. Each of the four vent holes in this plastic lid from a microwave meal has been given a water drop to form an array of four water drop microscopes.

I placed a “V” notch in the straw, and then, in a brightly illuminated room, placed the straw against the edge of the counter to keep it steady while bringing the end with the notch into focus under the water drop. Comparing the size of this notch in the water drop microscope with the size of the notch viewed with a 30X magnification pocket microscope, each of the differently sized drops was found to produce different magnifications, the greatest being between about 50X and 60X. I was also able to view the tip of a ballpoint pen in great detail, though both this image and the straw with the notch appeared dim.

The interesting aspect of this setup is that, very much like a modern compound microscope, different magnifications can be selected by rotating the desired water drop lens into position beyond the edge of the countertop. The main advantage is that no special tools or assembly of any kind is required.

A more advanced water microscope project can be found at ( http://bizarrelabs.com/micro.htm ). An interesting historical overview can be found here: http://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/art98/watermic.html

When I first attempted my own experiment, the lights were darkened, and a flashlight was stood on its end directly under the microscope. This created a shadow of the subject rather than sufficient illumination. However, when no subject was under the water drop, I did on one occasion look through it and see outlines of about ten spherical and tubular shapes. When a bright light shines in your eyes, shapes that are artifacts of the eye itself, sometimes called floaters, can appear, and they did in this instance. However, I could shake the lid to produce a jiggling motion in the water drop, which allowed me to identify which shapes were in the water drop and which were artifacts of my own eye. The shapes in the water drop were apparently static, but did tumble an drift towards the center of my field of view, presumable because they were drawn there by gravity due to the spherical shape of the water drop.

In a manner of speaking, it seems a water drop can become both slide and microscope. However, I'd be reluctant to rename this new arrangement a “water slide.”