Historical Experiments and Science Education - From Conceptual Planning of Exhibitions to Continuing Education for Teachers

Abstract

At the Deutsches Museum in München, we established in the department of education during more than 35 years a series of historical experiments and constructed apparatus for pedagogic purposes. We use these reproductions mainly for continuing teacher education within our department. At the exhibitions of the Deutsches Museum there exist many historical originals and reproductions but we seldom show historical experiments. However, in the new 1,000 square meter exhibition of astronomy, which was opened in 1992 we tried to implement some interactive historical devices.

Introduction

The philosophy behind the historical programs for education and exhibition activities at Deutsches Museum, Munich, Germany followed along eight different basic ideas, but which interact with each other.

These basic ideas are as follows:

History is a storehouse for useful but forgotten educational ideas and objects.

(see e.g. Faraday`s candle experiments.)

By detaching oneself from the present, the present becomes especially clear.

Similar processes may have developed in history, and characteristic differences become evident. (One may argue that the glasses you are wearing can best be studied by removing them.)

Science and technology—as new continents discovered by mankind in contrast to other areas of culture—become exciting and meaningful.

You should try ‘adventure’—excursions into history through objects and experiments with science assuming a personal aspect. Great scientists should be introduced also by their experiments.

In history, developments often proceed from the simple to the complex.

These led mankind, for example, from basic electrostatic experiments to complex electrical communication technology. This is similar to the development of a child’s understanding.

Historical case studies can be treated in detail.

Whereas the very complicated contemporary cases can often be discussed in the classroom only in simplified form.

Historical examples can demonstrate the interactions between culture, science and technology.

This provides a further opportunity to enrich students’ understanding of science and technology.

Experiments and apparatus can be used, as they relate to the present, for prognostic purposes.

(e.g.: the development of stable electric batteries in the 19.C.in comparison to the modern problem of batteries for electrical driven cars).

Especially considered for teacher training should be:

Teachers need background knowledge in addition to understanding their curricula even if they do not use it, e.g. historical experiments.

This background knowledge of experiments enables them to understand the whole context of their science in a more concrete way—even the philosophical context: for example asking the question what is an experiment? In addition, teachers become acquainted with different kinds of experiments where the question arises if there are any basic differences between observation and experiment, or the discussion of the relation between experiment and theory may take place.

Examples from the Exhibitions of Deutsches Museum

The interactive model “Homocentric celestial spheres of Eudoxos” (Lasserre 1966) (Fig. 1) was developed for a Copernicus exhibition in 1972, but thereafter was mainly used until today in teacher education and student lessons. We know that Eudoxos (4th century BC) was not only an astronomer but also an engineer. The function of the concept of his celestial spheres and their associated difficulties can be shown in a reconstruction with two movable rings (which was sold in the museum as a cardboard kit). For the daily and yearly movement of the sun Eudoxos used the rotations of two celestial spheres, the axes of which were inclined to each other by 23.5°. For the retrograde movement of the planets he needed three spheres, adding a fourth for their daily movement. To simplify his geometrical principles we used only two spheres. The ball at the inner sphere represents either the sun (to explain daily and yearly movement), or a planet (in the case of the movement of a planet). When, in the latter case, we rotate the outer sphere with constant angular velocity the inner one will stay with the heavy model planet at its lowest point. This corresponds to an opposite rotation with an equal angular velocity, just as described by Eudoxos. The resulting movement is a figure of “8” which Eudoxos called a hippopede, in comparison to the curve through which horses (hippos) are led during training. For physics teachers it is interesting to show that such curves really exist today when we look at the sky. Those geosynchronous satellites at a height of 36,000 km that don’t follow an equatorial path stray north and south increasing their range via a hippopede. From a quantitative point of view Eudoxos was not very successful. The advent of Ptolemaic astronomy abandoned homocentric spheres. However, these models are still fascinating from a pedagogic point of view and also from a philosophy of science perspective (e.g. the relation of model to reality, for example Fourier’s synthesis and the Greek crystal spheres).

Fig. 1

Model of Eudoxos spheres for the movement of the sun (or the hippopede-movement of a starlike planet)

The reconstruction of “Galilei`s laboratory” (Galilei 1974) (Fig. 2) as a whole Renaissance room within the exhibition of physics is something like fictional history. We don’t possess any exact knowledge what his laboratory in Florence looked like. Also the arrangement of all his famous experimental devices (inclined plane, water-clock, pendulum, telescope etc.) at the same time may never have been found in the exhibited way. But it is now possible to perform historical experiments in front of the visitors inside the exhibitions. This will be done regularly with seminars of teachers and students. The cultural background of the whole reconstructed architecture (sometimes supplemented by the use of Renaissance clothes for the demonstrator) is very useful for the total impression during experimentation.

Fig. 2

Reconstruction of “Galileo’s laboratory”

The so-called “Blink Comparator” (Drummeter 1991) in the astronomy exhibition (which opened in 1992—I was leader of the planning team), is a unique example, because it was possible to use the historically original one-only to implement a reconstruction of the blinking mechanism (Fig. 3). The optical beam path, of course, causes no damage to the original. This kind of comparator (invented in 1902) was the most important astronomical instrument—besides telescope and spectroscope—during the era of analog photography, to search for changes in the sky: two photographic plates of the same celestial field of view, but photographed at different times could be observed by aid of the blinking mechanism as only one field of view. Then every change in the sky became immediately visible by blinking points etc. For example Pluto, then the 9th planet of our solar system, was discovered by a blink comparator in 1930.

Fig. 3

The blink comparator within the astronomy exhibition

The discovery of the famous “Hertzsprung – Russell - Diagram” (Hertzsprung 1905, 1907; Russell 1914) (luminosity of stars plotted against spectral type—Fig. 4) is presented in the form of movable tablets. It is a simple but very helpful form of interaction: on the upper tablet there exist the original historical diagrams. Some questions posed to the visitor are added at the left. The tablet below the movable upper one will give the answers.

Fig. 4

The first drawn Hertzsprung–Russell-diagram, published by H. N. Russell

“The apparatus of Arno Penzias and Robert Wilson” from the 1960s is probably the most important scientific original from the 20th century in our museum.

It was combined by our workshops with a movable model (Fig. 5, at the left) of the whole historical “radio-observatory” to attract visitors to this complex object. But a multimedia supplement would be helpful to provide a better explanation. The content could be some information about the two physicists Arno Penzias and Robert Wilson and about their discovery: the theoretical predevelopment in cosmology, the original aim of the apparatus (it should test the first television signals between United States and Europe), the quality of this high technology device and the ultimate cooperation between the experimental group Penzias–Wilson and the theoretical group around Robert Henry Dicke; last but not least the final acceptance of the big bang theory.

Fig. 5

The apparatus, by which the cosmic background radiation was discovered

Examples, Taken from the Education of Student Teachers and from Teacher Seminars

We developed about 50 reconstructions of historical experiments. Here are four of them to illustrate the principles.

Galileo s “jumping hill experiment” (Figs. 6, 7, 8). Teichmann (1999, 2007) proved to be the most effective reconstruction for physics teachers. By the aid of a manuscript sheet of Galileo in Florence, folio 116v, we can look into his laboratory and reconstruct his private never published experiments.

Fig. 6

Galileo’s folio 116v from National Library, Firenze

Fig. 7

A reconstruction of Galileo`s “jumping hill”-device

Fig. 8

Smaller reconstruction with a plastic pipe

This sheet is the only proof we possess that Galileo really performed quantitative experiments, and that he compared measured values with the calculated ones. At the sheet we see a drawing with a vertical axis carrying the numbers 300, 600, 800, 1000 and two horizontal ones. Between these there are drawn five curves, starting almost horizontally at the intersection between the vertical axis and the first horizontal one. The curves end at the second horizontal axis where we also find different numbers (800, 1172, …).

Everyone who knows a little about Galileo’s free fall research, about his inclined plane experiments, and his description of cannon ball flights in the Discorsi will see that these curves are trajectories of free parabolic flights of bodies (or one body) starting at a common point. We may suppose that the numbers 300 etc. are the heights of fall in “punti” as Galileo expressed (equivalent to 0.9 mm). How to create such a parabolic flight? Quite easily: by means of a jumping-hill device, in which spheres roll down an inclined plane and at its end jump off horizontally. We do not know the exact shape of Galileo’s device (how steep it was, and so on), but in principle it had to be a device like the one in Fig. 7.

The whole example displays Galileo’s theoretical knowledge, as well as his experimental skill, and the conceptual problems he had to face. In other words, it shows in a nutshell some important parts of the real process of scientific research. In this article we can’t discuss all interpretations of this experiment Galileo also faced here the problem of rotational energy, which he could not explain. This leads to the pedagogic question: How should a scientist behave when he can’t solve a problem?

Altogether one can uncover in the sheet 116v several very different puzzles:

Was the intention of Galileo to test whether the horizontal distance of a ‘jump’ was proportional to the horizontal end velocity of the sphere, after rolling down the jumping-hill device?

The concept of instantaneous velocity and how this was measured was a big problem for Galileo and his time. It was a philosophical problem: is it possible to have an infinite number of different velocities between two fixed values of it? And it was a mathematical problem as well: how to deal with the instantaneous velocity when neither calculus nor analytical geometry were yet available?

Perhaps he accepted thesis 1 for whatever reason and wanted to prove by experiment that the end velocity is proportional to the square root of the height?

This interpretation, if true, would be of great importance, because v ~ √H is equivalent to the law of free fall H ~ t²! Had he accepted v ~ t, Galileo could easily obtain H ~ t² from v ~ √H.

But it is also possible that this is only the most interesting solution of this puzzle today rather than the true one!

Galileo could also have in mind to prove that the horizontal end velocity is conserved, or, in other words, is independent of the vertical motion.

We know, that resolving a motion into two components was an interesting methodological question for Galileo, at least, as far as its experimental confirmation was concerned. The conservation of “movement” was frequently used in his research of pendulum motion.

Maybe he tried to prove that the vertical free fall of a sphere after jumping off is subjected to the same law as its descent along the inclined plane.

Or, was his main purpose to discover the geometric form of the flight curve?

If so, then perhaps the experiment in question was intended to prove the trajectory of a horizontal free jump to be parabolic.

Maybe he also wanted to test the role of friction?

For most school purposes, it would be more convenient to have a smaller reconstruction of this device. The one easy to make is a pipe of metal or plastic at the end of which we fix a flexible strip of metal, so that the sphere can cross this connection without much friction. When the pipe’s inclination is changed, the end of the flexible strip can stay fixed horizontally. A more elegant device can be obtained by splitting up a plastic pipe, heating one end of it and bending this end to a certain angle. But in this case the inclination is fixed (see Fig. 8).

Shortly before 1900 we find “J. J. Thomson’s swimming magnets” as model for the atom (Thomson 1897; Kragh 1997; Davies 1997) (Fig. 9). Joseph John Thomsons experiment is of the few examples where a real mechanical model is used for research, not only for demonstration purposes. These are his swimming magnets as a two-dimensional model for his three-dimensional rosin cake atom. He himself didn’t invent the tool, but used it in an ingenious way, long time before computer models would have allowed to combine a repulsive force (between swimming magnets as electrons) and an attraction force (between a central magnet as model for the positive charge of the totally ionized atom and the swimming magnets). Based on his experiments Thomson found the concept of different shells of electrons inside the atom and the significance of them for the variation of properties of groups in the Periodic system of the chemical elements.

Fig. 9

Thomson’s swimming magnets as atomic model

In the specific configuration of 12 swimming magnets you also will get the two-dimensional model of a cubic ionic crystal—which goes beyond Thomson. (We simplified his model by using a solenoid coil round the glass bowl) (Fig. 10).

Fig. 10

Two-dimensional model of a cubic crystal

Around 1950 the German physicist Robert Wichard Pohl really constructed a “magnet model of a ionic crystal”—(Teichmann, Szymborski 1992) e.g. sodium chloride (Fig. 11). He also used it for research purposes to produce crystal defects. Small magnets with a thick (Cl) or thin (Na) plastic covering—corresponding to the ionic radii—were set parallel to each other, with north pole up (Na) and north pole down (Cl).

Fig. 11

Magnet model of sodium chloride

“Einstein’s last toy” (Fig. 12) (Cohen 1955) is one of the examples which mainly fits in our new programs of narrating science by history. It proves that science can be a playful adventure—even in very complicated branches like General Relativity Theory. This toy was presented to Einstein by a physicist, Eric Rogers, who visited him on his last birthday, on March 14, 1955, about 4 weeks before his death. It was constructed of a heavy small ball, a spring, a broomstick and other commonly available objects. It was about 1.5 m long at the top of which was fixed a plastic sphere, about 10 cm in diameter. Inside the plastic sphere ended a small plastic tube coming up from the long rod. Inside the tube a long weak spring was fixed together with a thread. At its end the small ball laid, outside the tube but inside the plastic sphere. Einstein explained the experiment to his next visitor, J. Bernhard Cohen:

Fig. 12

Reconstruction of Einstein’s last toy

You see this is designed as a model to illustrate the equivalence principle… The spring pulls on the ball, but it cannot pull the ball up and into the little tube because the spring is not strong enough to overcome the gravitational force which pulls down on the ball… Now I will let it drop and according to the equivalence principle there will be no gravitational force. So the spring will now be strong enough to bring the little ball into the plastic tube.

We reconstructed this toy in the Deutsches Museum by using a plastic rod, only 40 cm long, ending in the half sphere of a surprise egg for children, a plastic ball and a transparent plastic sphere about 10 cm in diameter (taken from a box filled with sweets). The function is perfect, like with Einstein’s original.

Conclusion

The program of reconstructed experiments was very successful in our teacher forthcoming training. Within the above-mentioned period of more than 35 years, about 50,000 teachers, among them many from foreign countries, were guests of our “Kerschensteiner Kolleg”.

The newest development, which we have tried for about 5 years, is “narrating” science by using history and historical objects.

The astronomy exhibition now belongs to the three or four most frequented places within our house. And so far we could test it, the reconstructions helped the visitors to get a more vivid contact to history, which otherwise remained more abstract for them.

This is valid particularly for Galilei’s laboratory.