Free What Mad Pursuit by Francis Crick

impoverished gentlemen). Incredible as it may seem, I had not realized that for many it was a highly competitive career.
    The Perutzes had lived for some time in a tiny furnished apartment very conveniently located near the center of Cambridge and only a few minutes’ walk from the Cavendish. They now planned to move into a suburban house, to have more room, and suggested to us that we might take their place. We were delighted with the idea and moved into The Green Door, as it was called, a set of two and one-half rooms and a small kitchen, at the top of The Old Vicarage, next to St. Clement’s church on Bridge Street, between the top of Portugal Place and Thompson’s Lane. The owner, a tobacconist, and his wife lived in the main body of the house while we occupied the attic. The actual Green Door was on the ground floor, at the back, leading to a narrow staircase that went up to our set of rooms. The washbasin and lavatory were halfway up these stairs and the bath, covered by a hinged board, was tucked into the small kitchen. It was often necessary to move a miscellaneous collection of saucepans and dishes if one wanted to have a bath. One room served as a living room, the other as a bedroom, while the smallest room was used as a bedroom for my son Michael, when he came home for the holidays from his boarding school.
    Odile and I had our leisurely breakfasts by the attic window in the little living room, looking out over the graveyard to Bridge Street and beyond that to the chapel of St. John’s College. There was much less motor traffic in those days, though many bicycles. Sometimes in the evening we would hear an owl hooting from one of the trees that bordered the college. We had only a small income but fortunately the rent was also very small, even though the apartment was rented furnished. The landlord apologized profusely when he felt compelled to raise our rent from thirty shillings a week to thirty shillings and sixpence. Odile luxuriated in her newly found leisure, read French novels in front of the small gas fire, and attended, informally, a few lectures on French literature, while I reveled in the romance of doing real scientific research and in the fascination of my new subject.
    The first thing I had to do was to teach myself X-ray crystallography, both the theory and the practice. Perutz advised me which textbooks to read and I was shown the elements of mounting crystals and taking X-ray pictures. Simple inspection of parts of the X-ray diffraction pattern usually gave, in a fairly straightforward manner, not only the physical dimensions of the unit cell—the spatial repeat unit—but also revealed something about its symmetry. Because biological molecules often have a “handedness"—their mirror image is not usually found in living things—certain symmetry elements [inversion through a center, reflection, and the related glide planes] cannot occur in protein crystals. This limitation reduces drastically the possible number of symmetry combinations, or space groups, as they are called.
    There is also a well-known limitation on rotation axes. Wallpaper can have a twofold rotation axis—it looks exactly the same if it is rotated by 180 degrees—or a threefold, fourfold, or sixfold one. All other rotational axes are impossible, including a fivefold one. This restriction is true for any extended pattern with two-dimensional symmetry, known as a plane group, and thus also for three-dimensional extended symmetry, or a space group. Of course a single object can have fivefold symmetry. The regular dodecahedron and icosahedron, which have fivefold rotational axes, were known to the Greeks, but what is allowed for a point group (which has no dimensions) is impossible for a plane group (of two dimensions) or a space group (of three dimensions). Moslem art, which for religious reasons is forbidden to depict people or animals (since the Prophet was very hostile to paganism), is often for this reason very geometrical