 | | | | |
| ||||
| be much simpler. One staff member built a large, adjustable but very rugged Michelson Interferometer. One could test the sensitivity of the instrument by watching the motion of the interference fringes that resulted from a very light pressure on the steel plate on which the interferometer mirrors were mounted. After doing so, I wondered how thick the steel plate was. I put a finger from one hand on top of the plate and tried to put a finger from my other hand underneath it, thereby using my hands as a crude set of calipers. But I was frustrated in doing so by a piece of plywood that 'blocked my lower hand. The problem was solved by raising the steel plate above the box on which it was mounted so that the visitors could see that the plate was made of 1/2" thick steel. In some ways an exhibit resembles a play or a musical composition. A tension is built up by something in the exhibit that elicits curiosity, or an interesting task, or a lovely effect, and then the tension is resolved as the result of aesthetic or intellectual payoff. If either component is missing, either the creation of tension or its relief, the exhibit is unsatisfactory. The creation of tension should not involve flamboyance or the high signal strength of traditional advertising. It should be a quiet affair, for if every exhibit shouts, "Hey Come and Look at Me," the museum will become impossibly tiring for the visitors. Although the two exhibits described above, the Gray Step and the Motor Effect, can be used in just one way, most of our exhibits can be used in many ways by the visitors and they are often used in an ingenious fashion that had not occurred to us when building them. When visitors can invent ways to use an exhibit they get a sense of discovery that is much more satisfactory than if they merely discovered what we thought they were supposed to discover. They stay with the exhibit for longer times and usually, but not always, end up by observing the behavior that we hoped they would when we conceived the exhibit. The exhibit Bernoulli Blower provides a clear example of such versatility. A large blower supports a ten inch rubber ball on a stream of air. The Bernoulli force is great enough that the |  | |||
| visitors can feel the tug when they pull the ball out of the air stream. If they tap the ball it will oscillate. They often attempt to toss the ball so that it is captured by the stream. They lift up their sweaters and let the air blow on their stomach. They lean over and let the air blow their long hair. They tear 'off bits of paper and watch them in the air stream. They try suspending other objects in the stream and sometimes they move off to the side and have a game of catch. Our exhibit Critical Angle is flexible in a different way. In many ways the exhibit is completely standard. It uses a Leybold 8" by 1-1/2" plastic semicylinder and two Leybold light sources. However, one of the sources has the cylindrical lenses removed in order to produce a diverging beam which can be focused by the large semicircular lens. The broad beam makes a very pretty pattern as the light converges in a caustic whose curvature is | ||||