Ben Franklin's workshop: celebrating a lifetime of invention.

Get out your party hat! January 17 marks the 300th birthday of Benjamin Franklin. You may have read about the scientist's most famous experiment: During a thunderstorm in 1752, Franklin flew a kite with a metal key attached to its string. The metal key became charged by electrons, or moving charged particles, in the lightning-filled sky. When electric sparks flew from the charged key, Franklin had evidence that lightning is a form of electricity. Franklin also made countless other discoveries and inventions. "These were simple gadgets to make life a little easier," says E. Philip Krider, an atmospheric scientist and Franklin historian at the University of Arizona. Celebrate Franklin's birthday by exploring some of his ingenious inventions.

Speedy Swim

The idea for one of Benjamin Franklin's earliest inventions came to him as a child while swimming. "He would show off for his friends and do tricks in the water," says Philip Dray, a Franklin historian. At 10 years old, Franklin fastened rounded paddles to his hands and feet. His gear--the world's first swim fins--helped Franklin swim faster and farther than before. "He would go under the water at one place and come up approximately 24 meters (80 feet) away," says Dray.

Like all swimmers, Franklin glided forward by pushing his arms and legs through the water. As he pressed on the water particles, each particle exerted an equal but opposite force against his limbs. That force propelled him forward. When he sported his new rims, each of Franklin's strokes pressed against a larger area of water. Result? More particles pushed back, and he swam faster.

Franklin eventually abandoned his fins because they were uncomfortable. But still seeking awe-inspiring speeds, he tested another swim booster. While floating in the water, Franklin tied one end of a kite string to his wrist. When the wind tugged on the kite, it pulled hint across the harbor. The downside? The wind only blew in one direction, so he had to find another way back.

Glass Music

In 1761, Franklin saw a musician playing an odd instrument: water-filled goblets. The musician rubbed his fingers around each glass's rim, creating echoing sounds. Franklin enjoyed the music, but he thought it was inconvenient to tote around water-filled glasses. So he invented an easy-to-carry glass instrument called the armonica.

Franklin set 36 glass bowls of different sizes on their sides. He threaded an iron rod through a hole in the bottom of each bowl. Then, he attached the rod to a foot pedal, which rotated the rod and bowls. When Franklin placed his fingers on the edges of the rotating bowls, the friction of his fingers rubbing against the bowls caused the glass to vibrate--creating sound waves. "It emitted this eerie sound," says Dray.

Like the keys on a piano, each bowl created a note with a different pitch. For instance, large bowls produced sound waves with a long wavelength (distance between a wave's peaks) and low frequency (vibrations per second)--leading to low-pitch, booming sounds.

Franklin's armonica caught on. In 1791, composer Wolfgang Amadeus Mozart wrote music to be played on it. "Franklin claimed [the armonica] was his favorite invention," says Dray.

Clear View

As Franklin aged, deteriorating eyesight inspired another invention: bifocals.

For a person to see clearly, light must focus directly on his or her retina, at the back of the eye. But Franklin had always been nearsighted. Distant objects appeared blurry because light bouncing off them focused too far in front of his retina. That's why Franklin wore glasses with concave lenses that were thicker at the edges than at the center. These lenses spread out incoming light, causing it to focus farther back--directly on his retina.

With age, Franklin also became farsighted: Light from nearby objects focused behind his retina. To see up close, he wore glasses with convex lenses that were thicker at the center than at the edges. These focused light farther forward.

The problem? "Franklin found changing his spectacles inconvenient," says Krider. So Franklin sawed in haft the lenses of each' pair of glasses. Then, he combined the halved lenses to make bifocals. The glasses' upper half contained concave lenses, so he could see far away. On the lower half, convex lenses helped trim peer up close.

Sporting bifocals, Franklin could easily enjoy his book collection. But he feared that reaching for books on the upper shelves could cause a bone-shattering fall. So Franklin created a long arm, or a wooden rod . tipped with two clawlike flaps. To safely grab a book, he would pull a cord at the arm's lower end, causing the flaps to pinch together and grip the out-of-reach book.

DID YOU KNOW?

* The popularity of the armonica faded in the 19th century, but a few musicians still play the instrument. It has even been used by the Metropolitan Opera Orchestra in New York City.

* Franklin founded a company that printed paper money. To prevent counterfeiting, he used a cast to produce images of real leaves on the back of the bills. He kept the process a secret. That way, counterfeiters could not figure out how to duplicate the fine details of the veins in the leaves.

CRITICAL THINKING:

* Franklin invented many simple gadgets to handle everyday inconveniences. Name some simple inventions that make your daily life a little easier.

CROSS-CURRICULAR CONNECTIONS:

SOCIAL STUDIES: In addition to being a famous scientist, Benjamin Franklin is the only person to have signed 'all of the four major documents that created the United States as an independent country. These documents include the Declaration of Independence (1776) mid the Constitution (1787). Do research to write a report on the significance of one of these four documents.

RESOURCES

* For information on a traveling exhibition on Benjamin Franklin, see: TE 8

* You can play a virtual armonica at this Web site from the Franklin Institute: http://fi.edu/franklin/

* This interactive Web site is filled with information about Franklin: www.pbs.org/benfranklin

(PAGE 12) BEN FRANKLIN'S WORKSHOP

DIRECTIONS: Fill in the blanks to complete the following sentences.

1. As a swimmer pushes his or her limbs through the water, each particle of water exerts--an but--force against the limbs. Swim fins allow a swimmer to press against a--of water. As more particles push back, the person can swim--.

2. The large bowls in an armonica produce sound waves with a long--(distance between a wave's peaks) and low--(number of vibrations per second)--leading to low-pitch, booming sounds.

3. For a person to see clearly,--must focus directly on his or her--,at the back of the eye.

4. The upper half of--glasses contain--lenses, which help a person to see far away. The lower--lenses allow a person to peer up close.

ANSWERS

1. equal, opposite; larger area; faster

2. wavelength, frequency

3. light, retina

4. bifocal, concave; convex