How to Use a Magnifying Glass and the Sun to Burn Wood

Focusing the sun's light with a magnifying glass is one way to start a fire.

Humans have known since ancient times that you could start a fire by focusing sunlight. Legend has it that famed mathematician Archimedes used large strategically-placed mirrors to set fire to attacking Roman ships during the siege of Syracuse. While you may not have any attacking ships you need to burn, you'll still encounter situations where you need to start a fire while camping. If you don't have any matches handy, a magnifying glass will do the trick.

Things You'll Need

• Magnifying glass
• Firewood
• Kindling (twigs, sticks etc.)
• Newspaper

Instructions

1. Find a safe place to start your campfire -- preferably inside a fire ring, fire pit or other designated site. Make sure that park regulations allow campfires. Also make sure that the fire ring is far away from anything else that could start or catch fire (trees, brush, grass, etc.)

2. Place several pieces of firewood inside the ring so their ends lie atop each other. Add some twigs and small sticks for kindling and some scrunched-up pieces of newspaper.

3. Hold the magnifying glass over the newspaper so it focuses the sunlight into a small bright dot. Move the magnifying glass toward or away from the paper until the dot formed by the sunlight is as small and bright as possible.

4. Make sure the magnifying glass is held at the correct angle. If it is held at the wrong angle, the sunlight will form a large diffuse patch. Hold the magnifying glass so that the sunlight forms a small dot on the newspaper.

5. Hold the magnifying glass steady. It could take anywhere from five to 15 seconds for your newspaper to light. Once it is lit, the flames will spread to the kindling and the wood, and you'll have a fire going.

Tips & Warnings

• You can also direct the sunlight straight toward a twig to light it on fire.

• ALWAYS be careful when starting or adding fuel to a fire. Never leave a fire unattended even for an instant. Do not try to light fires if park regulations do not permit it, and only start fires in fire pits, fire rings or other designated areas for safety.

References

• Wildwoods Survival: Magnifying Lens
• "Physics for Scientists and Engineers"; Richard Wolfson, et al.; 1999
• Navigational Aids for the History of Science, Technology and the Environment: Archimedes of Syracuse