The Art of Science: Ben Franklin's Harmonica


Inspired by musical wine glasses he heard played in Europe, Ben Franklin invented a mechanical glass harmonica in 1761. The instrument fell out of favor in the next century and was not heard again until 1982, when German-born glassblower Gerhard Finkenbeiner brought it back to life. Finkenbeiner heard about the instrument while living and working in Paris in the 1950s. Using original plans and drawings, he reinvented the modern glass harmonica.

Curriculum Links
Related Frontiers Shows and Activities
Introduction: Good Vibrations
Activity 1: See and Touch Sound
Activity 2: The Sounds of Music
Activity 3: Franklin's Inspiration
Extensions



CURRICULUM LINKS


CHEMISTRY

glass
HISTORY

Ben Franklin
MUSIC

PHYSICAL SCIENCE
PHYSICS

acoustics, frequency, sound




RELATED FRONTIERS SHOWS AND ACTIVITIES

Expedition Panama (Show 801): Echoes in the Night
Inventing the Future (Show 701): Brain Music


INTRODUCTION: GOOD VIBRATIONS

Sound is created by vibrations that produce sound waves. The speed of the vibration, or frequency, determines the pitch -- high or low -- heard when the waves strike the ear drum, which translates the sound into a nerve impulse that is processed by the brain. All materials have a natural frequency of vibration. Glass used to make glass instruments starts to "sing" when the vibration gets the molecules moving at their natural frequency. By building and playing homemade instruments, you can see how various materials produce different sounds, and "exp-ear-ience" the good vibrations we call music!



ACTIVITY 1: SEE AND TOUCH SOUND

Some sounds are easily interpreted when they reach your ear. For example, when vocal cords vibrate at a high frequency (fast), a shrill or high-pitched sound will result, which might be an expression of fright. At a low frequency (slow), a low-pitched sound is produced, like a growl, which could be a warning of impending danger. Without a sense of hearing, can you determine what kind of sound is being produced?

OBJECTIVE

Explore the world of sound with hearing and other senses.

MATERIALS
high- and low-pitched tuning forks (use forks of similar sizes)
glass of water
ear plugs
blindfold
PROCEDURE

Students can work in pairs for this activity. One student is the observer or subject, the other student the assistant.
Blindfold subjects and have them listen to high- and low-pitched tuning forks until they can recognize the sound generated by each. Have the assistants strike the forks so subjects use only their ears to "gather data."
Remove the blindfolds and have the subjects put in ear plugs. (They may need to wrap a bandanna around their heads to further block the sound.)

Assistants should strike one of the tuning forks and hold it in a glass of water. Ask if the subjects can identify which frequency tuning fork it is by looking at the water.

Repeat the procedure with the other tuning fork.

Next, replace the blindfolds on the subjects (still wearing earplugs).

Give the subjects one of the tuning forks and tell them to strike it.

Ask subjects to try to identify which frequency tuning fork they are holding, just by how it feels when it vibrates.
Note: If you use tuning forks for different notes, like A and C, you can detect a difference in how the vibrations cause water to move, but it is subtle. It takes practice to see and feel differences in the forks.

QUESTIONS
Is it possible to perceive sound without using your ears?

What evidence did you use to identify low and high frequencies?

How do animals interpret sound vibrations without using a sense of hearing (bats and snakes, for example)?

An easy way to "feel" vibrations is to place your index finger on your neck and start with a growl (low frequency) and increase the sound in your throat to a higher pitch (high frequency). Can you feel the speed of the vibration in your vocal cords with your fingertips?


ACTIVITY 2: THE SOUNDS OF MUSIC

Some of the main instruments in an orchestra or band use "wind" to create a vibration in a reed to make a sound. In this activity, use a straw to make a crude reed-like instrument you can experiment with to produce sounds.

OBJECTIVE

Find out how different length straws influence sound by modifying frequency.

MATERIALS
plastic straws
PROCEDURE
Cut the corners of a straw to form a mouth-piece. (These are rather crude reeds.) Press the two sides of the cut straw together to flatten them.

Place the cut end between your lips and close your lips to bring the two sides close together.

Blow through the straw until the cut end vibrates and produces a sound. You may need to blow very hard and vary the pressure with your lips to produce the sound. If you can't make a sound, flatten the cut end more.

Once you are producing a sound, keep blowing and cut off small bits (1 or 2 cm at a time) of the straw to hear how the sound changes.
QUESTIONS
How does changing the length of the straw affect the sound?

How does the sound produced relate to frequency of the vibrations? (high frequency or pitch = fast vibrations; low = slow vibrations)

Can you use two straws (one slightly larger than the other) to create a trombone-like instrument?


ACTIVITY 3: FRANKLIN'S INSPIRATION

Franklin's instrument, which he called a glass "armonica" after the Italian word for harmonica, is a series of glass cups on a rotating, horizontal spindle. Each cup represents one note of the musical scale. One instrument is composed of two or three octaves. Today's glass harmonica is also made from a series of glass bowls or cups, but Gerhard Finkenbeiner uses only quartz or pure crystal glass. Impurities in the glass affect the vibrations; the purer the material, the more likely the molecules will all vibrate at the same frequency.

Musical experience helps in learning to master this sensitive instrument, but you don't need crystal to produce sound. You do need carefully washed hands, clean water and damp fingers to make music.


OBJECTIVE

Experiment with different glasses, much as Franklin did, to try to produce musical sounds.

MATERIALS
glasses (a variety is good; wine glasses are best)
butter knife, spoon or other metal utensil
pitcher of water
Note: Glass wine glasses are recommended because of their shape and the thin glass. Water goblets will also work. Experiment with various shapes, sizes and kinds of glass. The thinner and purer the glass, the better the sound.

PROCEDURE
Start with one glass and tap it gently with the utensil.

While tapping the glass, pour water into it about 2.5 cm at a time. Listen and have another student record how the sound changes as the water level increases.

Repeat the procedure with different glasses and record the effect the shape or type of glass has on the sound generated.

Repeat Steps 1 through 3. Instead of tapping the glass with the utensil, wet your finger and rub it around the edge of the glass until a sound is produced. (Make sure your finger is clean before you start and keep it wet. It takes practice to produce the eerie sound.)

Try to fill separate glasses so that you are able to play a simple tune with the knife or your finger, like "Mary Had a Little Lamb." If you can tune the glasses to specific notes, mark the notes on the glasses and indicate the water level with a marker. (In the glass harmonica seen on Frontiers, the cups with gold rims indicate sharps and flats.)


EXTENSIONS:

Experiment and see who can master the glasses to play more complex music.

Try to build different instruments (string, wind, percussion) and conduct a "silly symphony" at your next assembly.


http://www.pbs.org/safarchive/4_class/45_pguides/pguide_804/4484_franklin.html