Structural and Mental Models - Essentials of Chemical Education - page 174

Fig. 6.17 (a) An illustration of the equilibrium with the “Apple fight,” Part 1 [ 24 ].
Continued.
Science history also offers many examples. Watson [ 25 ], to only name one, cut out
the shapes of base molecules from cardboard for the prognosis of base-combinations
in the assumed DNA double helix: “The purine and pyrimidine models that I needed
were not ready in time. So I used the whole afternoon to cut out exact models from
thick cardboard. I started to move the base models back and forth and arranged them
in pairs in every possible combination. Suddenly I realized that an adenine-thymine
pair, which was held together by two hydrogen bonds, had the same shape as a
guanine-cytosine pair” [ 25 ]. These sentences indicate the importance of very simple