Well, not directly. No one can do that, they’re too small. They’re so small that you can’t even see them with the most powerful light microscope. They’re dimensions are less than the wavelengths of visible light. In effect, light misses them.
So you zap them with a tightly focused x-ray beam – much shorter wavelengths – and the beam scatters onto a photographic emulsion or, these days I guess, on to some micro-electronic detector and get an image. Which looks like a smudge. But, from such smudges you can deduce what the thing must look like.
That’s where Geis came in. He takes those deductions, which have been rendered as sketches of some sort, and turns them into useful and elegant images, images that make sense to the naked eye. These images are at once true to the molecule and to the eye, but they are also fictions. Because, as I said, they’re way too small to be visible themselves. So Geis had to come up with plausible visualization.
Many others have painted molecules, but Geis was the first. You can find nice appreciations at L2Molecule and at Brain Pickings, which covers some of his other scientific visualizations. This Google query pulls up a bunch of images.
Here’s a passage about Geis from an article* I wrote on visual thinking:
In a personal interview, Geis indicated that, in studying a molecule's structure, he uses an exercise derived from his training as an architect. Instead of taking an imaginary walk through a building, the architectural exercise, he takes an imaginary walk through the molecule. This allows him to visualize the molecule from many points of view and to develop a kinesthetic sense, in addition to a visual sense, of the molecule's structure. Geis finds this kinesthetic sense so important that he has entertained the idea of building a huge model of a molecule, one large enough that people could enter it and move around, thereby gaining insight into its structure. Geis has pointed out that biochemists, as well as illustrators, must do this kind of thinking. To understand a molecule's functional structure biochemists will imagine various sight lines through the image they are examining. If they have a three-dimensional image on a CRT, they can direct the computer to display the molecule from various orientations. It is not enough to understand the molecule's shape from one point of view. In order intuitively to understand it's three-dimensional shape one must be able to visualize the molecule from several points of view.
Think about that for a minute. In order to visualize a single tiny molecule, Geis used his entire body.
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* William Benzon. Visual Thinking. Allen Kent and James G. Williams, Eds. Encyclopedia of Computer Science and Technology. Volume 23, Supplement 8. New York; Basel: Marcel Dekker, Inc. (1990) 411-427.