======Low Tech Microscopy======

Microscopes are powerful tools for teaching biology, and many of their bene- fits are hard to replace with local fabrications. However, simple materials can be used to achieve sufficient magnification to greatly expands students’ under- standing of the very small. They may view up close the anatomy of insects and even see cells.

=====Water as a lens=====
Water refracts light much the way glass does; a water drop with perfect cur- vature can make a powerful lens. A simple magnifier can be made by twisting a piece of wire around a nail and dipping the loop briefly into some water. Students can observe the optical properties of the trapped drop of water.

=====Perfect circles=====
Better imaging can be had if the drop is more perfect in shape – the asymmetry of the wire twisting distorts the image. Search for a piece of thin but stiff plastic – the firm, transparent packaging around new cell phone batteries works well. Cut a small piece of this plastic, perhaps 1×2 centimeters. Near one end, make a hole, the more perfect the better. The best hole-cutting tool is a paper hole punch, available in many schools. With care, fine scissors or a pen knife will suffice; remove all burrs.

=====Slides=====
A slide and even coverslip may be made from the same plastic, although being hydrophobic they will not have the same properties of glass when making wet mounts. Improvise a method for securing the punctured plastic over the slide; ideally the vertical spacing can be closely adjusted to focus.

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=====Backlighting=====
On a bright day, there may not be any need for additional lighting, but in most classrooms the image will be too dim to be easily seen. The sun is a powerful light source, though not always convenient. Flashlights are generally inexpensive and available; many cell phones have one built in the end. To angle the light into the slide, find either a piece of mirror glass, wrinkle-free aluminum foil, the metalized side of a biscuit wrapper, etc.

Experiment with a variety of designs to see what works best given the ma- terials available to your school. If you use a slide of onion cells stained with iodine solution (see Sources of Chemicals), your students should be able to see cell walls and nuclei.