1. 1
Exhibits Designed and Built By Richard Gagnon
Oct., 2016
AT THE SCIENCE MUSEUM OF MINNESOTA
Electricity Bench (a.k.a. AC-DC Bench)
Even when experimenting with simple electrical circuits, the wiring quickly becomes a quit
confusing mess. To alleviate that, we mounted various electrical components on to
blocks. The blocks have copper caps mounted at each end, and several small magnets are
arranged inside each cap, so that the blocks can be electrically connected to each other
very quickly. Consequently, there are no wires needed for the circuits and the lay-out of
any circuit construction is easy to follow.
The original bench had a 5 volt DC supply only. Soon after, an AC supply was added, along
with an oscilloscope. Visitors could then explore the difference between AC and DC
electricity. One can see that light bulbs and resistors work the same way with either
supply. But that our AC motor works only on AC and our DC motor works only on DC.
Also available are: rectifiers, LEDs, a capacitor a dismantleable transformer and a solenoid.
Electronics Bench
Numerous electronic circuit boards are mounted to their own plastic blocks. One or more
blocks can be placed on a pair of copper rails which supply power to the blocks. The blocks
can be connected end to end. The inputs are applied to the left of each block; the outputs
are on the right. All signals can be viewed on an oscilloscope. Each block can perform a
task. Among the blocks, there are:
An amplifier: A voltage applied to the input is amplified and the result appears on
the output. The output can be connected to a speaker.
Radio receiver: This one can pick up local stations and the block’s output can be
amplified or otherwise modified.
Radio transmitter: an audio signal can be applied to the input. The output can be
picked up (wirelessly) by the receiver.
Light detector: A light source will cause this block to produce a voltage at its output.
It will also pick up signals from an ordinary TV remote.
Oscillators: There are two. One works in the audio range, the other in the sub-
audio. They can each be connected to each other.
In the electronics engineering world, we often buy and connect up various electronic
devices in some way so as to achieve some result. We often don’t need to understand just
how the devices (or our blocks) work. We only need to understand what inputs are needed
to get a desired output.
(Many people worked on this project including Aaron Heidgerken, Jim Willmore and Chris
Burda.)

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Electro- larynx
These devices are used by people who have lost use of their vocal chords. Griffin
Laboratories donated one their devices, which we modified extensively. The Griffin model
has a pitch control, so now, when visitors learn how to use our version, they can get a good
sense of how the larynx, throat and mouth all work together to generate speech.
Optics Bench
This exhibit works much like the familiar students' optics bench, with these differences:
The lenses, pin-holes, screens, etc. are permanently mounted to their respective holders.
The holders are made so that all of the various optical components can be brought right
next to each other when they are slid along the bench. Instead of a fixed scale mounted
to the bench, a pair of tape-measures have been mounted together in a way which makes
is quite easy to measure distances between various elements.
Numerous optical phenomenon can be investigated: The simple projection of a real
image, the effect of stops, the rule for magnification, the workings of microscopes,
telescopes, pin-hole cameras, and other devices.
(Built in collaboration with Kit Kube.)
RC Bench
The user may arrange resistors, capacitors and a neon bulb so that the bulb flashes
regularly. One of the capacitors consists of nothing more than two 15" x 15" metal plates
separated by a thin sheet of plastic. A resistor may be constructed by drawing a heavy
pencil line on a piece of paper and then placing it in the circuit. A special, high impedance
(109 ohms) volt meter was constructed to monitor voltages in the circuit.
(Built in collaboration with Mike Maus and Tom Gagnon.)
Flame Spectrometer
The visitor may introduce small samples of any of six chemical solutions into a Bunsen
burner flame. The flame then turns color. The color, which is due to the ionization of the
chemical elements, indicates what elements are in the solution. The flame may be viewed
through a spectroscope.
Crackometer
This device demonstrates the importance of wearing a helmet when riding a bicycle. The
visitor causes a 1 pound hammer to fall and strike a steel plate. Strain gages on the plate
measure the force of the hammer blow. The visitor may insert a 1/4" pad between the
hammer and the plate. When the hammer falls again, there is a dramatic difference in the
force that the plate experiences. This is because when the pad is in place, the
decelerating force of the hammer is spread over a longer time. The peak force on the
plate is displayed on a large meter.

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Building Insulation Exhibit
All materials that we use to insulate our buildings are in fact much poorer insulators than
air. The exhibit shows that the insulating material's job is to keep the air from moving. If
the air cannot move (by convection or just by the wind) then it won’t transfer heat by
conduction to a building’s walls. Heat transfer by radiation is also explored.
Electrocardiograph
The visitor grasps two copper handles. The heart's electrical signal is displayed on a
storage oscilloscope. The oscilloscope's image can be frozen by a visitor’s moving one of
the handles forward. The visitor can see and identify the characteristic parts of the wave
form.
Transformer Bench
The visitor may assemble a transformer in several different ways. The incoming voltage
can be "transformed" into a high or low voltage. We included a watt meter. The meter
shows the inefficiency of our home-made transformer and shows that we never get
something for nothing. Voltage or current can be increased when passed through
transformers, but not the wattage.
Magnetizer Bench
Different metal rods can be placed in a wire coil. A large current (900 amps) passes briefly
through the coil windings. This will magnetize some rods but not others. The rods can
also be demagnetized.
Transmission Lines
This exhibit demonstrates why our power company transmits electrical power at such very
high voltages. It also shows why our power is ac, not dc. Small houses with light bulbs in
them can be connected via a longish "transmission line" either directly to a 5 volt source.
Or the houses can be connected in a more complicated way: the source is first stepped
up by a transformer to 40 volts, then stepped down to the usable 5 volts.
Strobe Light
A strobe light was mounted to a table so that several devices can be viewed while they are
in operation. Devices include a sewing machine, an electric toothbrush and a simple
spinning disk.
Strobe Wheels
Instead of viewing objects with a strobe light, visitors view objects through a spinning disk
with a radial slit in it. This allows viewers to see that the light emitting from neon signs,
fluorescent lights and television screens are changing rapidly over time. Many people are
quite surprised to see that a picture on a television screen is in fact dark most of the time,
and that the picture we see is generated by a bright line scanning from top to bottom.

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Musical Spots
We felt that we should have a wheelchair-accessible version of the Musical Stairs. We
needed a clearly defined path, and we needed a reliable way to detect people when they
traveled on it. The solution to the first need was to use small theater lights to make
several well-defined light-spots on the floor. The solution to the second problem was to
make small telescopes, each of which would look down on one light spot. If a visitor
stepped on a light spot, a photo-detector would see the shadow. This causes a musical
note to be sounded, and for the light-spot to go off for a few seconds.
Blink Comparator
Since the earliest days of photography, astronomers have used blink comparators to
watch for changes in the night sky. The planet, Pluto, for example, was found this way. A
photograph was taken of an area of the sky. Weeks later, another photograph was taken
of the same place. The two photographs were placed in a blink comparator. This machine
allows an astronomer to switch rapidly between the view of one photograph and then the
other. Pluto appeared as a single tiny speck that seemed to jump back and forth as the
photographs were switched. Our blink comparator allows visitors to view several pairs of
photographs and attempt to find some change between each pair.
Electrostatic Smoke Trap
One of the several pollutants generated by coal-fired power plants is a fine dust of
unburnable minerals. These can be trapped by subjecting the flue gases to a high voltage.
The micrometer sized particles will take on enough charge so that they can be drawn to
plates of an opposite charge where the particles stick.
In the exhibit, the public can turn our smoke generator on, watch smoke rise into the air,
and then turn on the electrostatic trap. One then sees that the smoke is trapped.

5. 5
EXHIBITS PROJECTS AT THE EXPLORATORIUM:
Mathematics
Brazil Nuts
When a box filled with small parts is shaken, large objects tend to rise to the top, even if
the large ones are denser than the small ones. This exhibit has been built to show this in
two dimensions. (Built in collaboration with Claire Pillsbury)
Catenary Arch
Visitors construct a free standing arch from non-interlocking blocks.
Fading Motion (a.k.a. Sand Pendulum)
This pendulum is viscous-damped. While it swings over a conveyer belt, a stream of sand
runs out of the pendulum bob (actually a funnel) and draws a damped sine wave on the
belt. The damping is exponential.
Hyperbolic Slot
A three foot long, straight stick can be made to pass through a curved slot. This can
happen because, as the stick is made to move, it describes a hyperboloid in space.
Non-Round Rollers
A flat board rolls smoothly over the tops of two rollers. The rollers are obviously not
round. It turns out that a circle is but one member of a whole family of shapes with the
property of having a constant width.
Planimeter
Planimeters are devices used to measure the areas of irregular shapes drawn on paper. A
highly museumized planimeter is displayed. In explaining its operation, some of the basic
principles of calculus are shown.
Scaling
It is surprising to most people to discover that large and small structures behave very
differently, even though they are exact scale models of each other. In this exhibit, four
plastic strips are mounted on a common block. Each strip is a scale model of its neighbor.
When the block is rotated, the small strip can easily be made to stand on end like a blade
of grass. The largest strip cannot stand at all.
Square Wheels
A car with square wheels will roll smoothly over a surface. However, the surface cannot
be flat. For polygon-shaped wheels, the surface must be a series of catenaries. (Built in
collaboration with Jack Tessman)

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Mechanics
Bernoulli Levitator
A blower blows air downward, out of the ceiling of this exhibit. When a 10 inch plate is
pushed up close to the hole, the plate is suddenly supported by the air stream, and held
close to the ceiling. Bernoulli’s principle that a fluid’s pressure will decrease as the fluid’s
speed increases is demonstrated.
Bicycle Wheel Gyro
Various gyroscopic effects can be seen, using bicycles wheels mounted to handles. We
basically took a classroom demonstration and turned it into an exhibit. (Built in
collaboration with Jeff Adams)
Doppler Exhibit
A "Sonalert" noise maker is attached to a belt which runs over pulleys 20 feet apart, one
above the other. When a visitor turns a crank, the noise maker travels towards and away
from the visitor, and the Doppler shift can easily be heard.
Falling Feather
A feather, along with a second, much denser, object, can be made to fall in a 6 ft. long
evacuated tube. That the two objects fall at the same rate in a vacuum can be clearly
seen. (Built in collaboration with Tom Tompkins)
Foucault's First Pendulum
A thin, two ft. long rod has one end mounted to a heavy base. The visitor plucks the free
end so that it oscillates. The base can be rotated, so that it can be seen that the plane of
oscillation of the rod stays fixed while the base is rotated beneath it, thereby
demonstrating how large "Foucault Pendulum" exhibits can reveal the rotation of the
earth.
Pendulum Table
Behaviors of simple pendulums are shown. A clock escapement is also demonstrated.
Resonant Pendulum
The visitor can set in motion a large concrete pendulum by pulling on it with very weak
magnet, provided that the pulling is in phase with motion of the pendulum. The
pendulum hangs by a 30 ft. cable. (Built in collaboration with Joe Ansel)

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Heat and Temperature
Curie-Point Motor
A light shines on the rim of a wheel. The rim is made of an alloy whose curie-point is only
a little above room temperature. The heat from the light is enough raise the metal above
the curie-point in just one spot. There is a magnet near this spot, and because of an
unequal pull of the magnet, the wheel is made to turn continuously. (The originator of
this device is not known to us.)
Thermocouples
The heat from one’s hand creates a weak current through the junction of dissimilar
metals. Also the reverse effect is shown: current forced through a junction will pump
heat, giving us a solid-state refrigerator.
Water Freezer
A small quantity of water is made to freeze by evaporating part of it in a vacuum
chamber. Boiling water, covered with ice, may be observed. Visitors may open the
chamber and remove the ice.
Electricity and Magnetism
Magnetic Lines of Force
Steel rods have been inserted into ½” acrylic balls. The balls are placed in 25 spaces in a
sealed acrylic box which is filled with oil that matches the index of refraction of the
plastics. The result is that when the box is brought near a large permanent magnet, the
magnet lines of force can be easily seen in three dimensions.
Magnetic Sand
...consists of a large permanent magnet mounted in a shallow tray. The tray contains
magnetic sand (magnetite). Visitors are free to play with and observe the interaction
between the sand and magnet. The magnetite is beach sand so the grains are quite
spherical. Consequently, the sand has a very pleasant feel, quite unlike the gritty feel of
iron filings.
Sand Sorter
The public is recruited to turn a crank and sort our magnetic sand from beach-sand.

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Physics of Light
Blue Sky
A beam of white light enters a clear plastic tube from one end. The tube, which is filled
with a suspension of protein gelatin, scatters polarized blue light at right angles to the
incoming beam. The blue light is due to Rayleigh scattering, the same process that causes
the sky to be blue.
Michelson-Morely Interferometer
The operation of this famous device is shown. In one experiment, air can be removed
from a small chamber mounted on the interferometer, and the resultant change of the
speed of light in the chamber can be seen. (built in collaboration with Dave Flemming and
Charles Gloriosso)
Stress Analyzer
Using polarizers and a quarter-wave plate, mechanical stresses can be seen in clear plastic
models of objects.
Zoom Lens
...shows the movement of the two lenses needed to make a zoom lens work. This piece is
now at the Discovery Center of Idaho.
Perception
Ames Room Explainer
....shows the underlying geometry that makes possible the construction of the well-known
Ames Room exhibit. (Built in collaboration with Tom Humphrey)
Land Effect
The eye-brain system has an extraordinary ability to discern the innate color of objects
even if the ambient lighting is varied a great deal. This experiment teases out the strategy
used. In the exhibit, two black and white pictures are superimposed, one illuminated with
green light, one with yellow. The visitor perceives a full color image of the scene. (photo
transparencies supplied by the Polaroid Corporation.)
Peripheral Vision
The exhibit consists simply of a big protractor mounted on a table. It shows that, without
moving our eyes, we have a great panoramic view, more that 180 degrees wide. But of
that view, only a tiny 2 degrees of it is seen in clear detail. That we perceive the visual
world around us in clear detail even though we see it through a kind of fuzzy tunnel vision
was one of the biggest revelations that I have gotten since starting to work at the
Exploratorium.

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Persistence of Vision
The visitor looks through a three foot long tube that has a narrow slit over the far end.
When the tube is held steady, little can be made out of the scene that the visitor is trying
to look at through the tube. If the tube is swung from side to side, the scene is
immediately discernible.
Touch Sensitivity
A piston mounted in a block can be moved in and out, and made flush with one of the
piston's surfaces. One's ability to detect a small step between the block and the piston
can be measured in increments of .0001 inch.
Navigation
Celestial Navigation
A globe of the earth has been placed beneath a small bright light that represents the Sun.
The exhibit shows how you can, first, determine the Sun's position over the earth if you
know the time (in Greenwich, England, for example) and date. Second, your own distance
from the Sun's position can be determined by measuring the Sun's angle above the
horizon.
Celestial Tools
A sextant, astrolabe, back-staff and cross-staff are displayed. Visitors can try using them
to measure the angle between a small light, representing the sun, and a "horizon" painted
on a distant wall.
Loran Lines
Using string and pulleys, the exhibit demonstrates how loran navigation works. The
exhibit also demonstrates a way in which the hyperbolic curve can be defined.
Orrery
This is a commercially available model of the Solar System that has been strengthened and
mounted to a table top. It augments other exhibits that explain celestial navigation.
Self-Centered Globe
A globe of the earth has been fixed in position so that its axis is aligned with the earth's
axis, and San Francisco's location on the globe is positioned topmost. The globe has been
placed in a sunny area. In this configuration, the Sun's motion and the shadows it can
create are the same on the globe as they are on the earth. The principles of celestial
navigation can be readily demonstrated. (Globe constructed by Ned Kahn.)

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Miscellaneous
Scanning Electron Microscope
An SEM was donated to the Exploratorium. A great deal of work was done to, first, repair
it, and then to make it suitable for the public to use. They could examine any of six
specimens that we had prepared. Usually the public worked with this exhibit on their
own, but the exhibit worked best when volunteers were there to demonstrate it. The
Exploratorium trained new volunteers regularly. (Project was executed in collaboration
with Stan Axlerod.)
Heliostat
This device was built to supply sunlight for Bob Miller's "Sun Painting". It now, also,
supplies light for "Pin-hole Sun Image" and Bruce Sams' "Solar Signature".
Free Junk
....consists of a large wooden box that the staff fills with things that are too
good/neat/interesting to throw away but are of no real value to the museum. Our visitors
then carry the stuff off.
Not For Free Junk
The Exploratorium keeps a counter-top showcase filled with a variety of things that
actually have some monetary value, and these things are sold to the public.
Valve of Some Sort
(built in collaboration with Larry Shaw)

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EXHIBITS PROJECTS AT
THE DISCOVERY CENTER OF IDAHO
Slit Lamp Microscope
This is the standard instrument used by ophthalmologists for examining the eye. Ours
was donated by the Lyons Club of Boise. It is an elegant piece of equipment, and can be
used to examine many parts of the eye, but the part that is most fascinating and easiest to
view is the iris. For now, the instrument will only be demonstrated by a trained volunteer.
Doppler Blood Flow Exhibit
Blood flow through the arteries and veins can most effectively monitored by a small ultra-
sonic probe that sends out a continuous wave. Sound reflected from the moving blood is
doppler-shifted, and can then be detected by the same probe. The difference between
the transmitted frequency and the received frequency is detected and can be heard over
a speaker or displayed on an oscilloscope. For the exhibit, we used the standard medical
doppler-detector unit, and connected it to an electrocardiograph monitor, which, for us,
functions as a very nice storage oscilloscope.
Bone Stress,
Bicycle Legs
These two exhibits were copied from plans from the Exploratorium.
Hydraulics Lab
Ratios of the areas of hydraulics pistons is demonstrated. The not-so-obvious workings
of a gear-pump are shown.
Arthroscopy Demonstration.
Visitors can attempt to manipulate surgical manipulators while viewing their work
through an arthroscope.