We owe chemists and physicists our knowledge of the composition of living matter, of the conversion of the sun’s heat into chemical energy, and of the myriad molecular interactions that sustain life. Steven Vogel’s Cats’ Paws and Catapults is the first book that has made me look at biology through the eyes of an engineer and compare the mechanics of animals and plants with the objects produced by man. At first sight this project looks unpromising. How can you compare organisms that consist predominantly of carbon with machines that are made of metals? Many of nature’s engines are on the molecular scale, which means that they are about 100 million times smaller than a car engine. Man’s artifacts are deliberately designed, while nature’s structures have evolved blindly, haphazardly, over millions of years, by the reshuffling of genes, by mutation and natural selection of features that have led to more successful offspring. On the other hand, this very success requires living organisms to be constructed on sound engineering principles, which Vogel tries to explain.
He describes how nature has sometimes inspired man’s engineering designs. Otto Lilienthal, the German engineer, who was the first man to have lifted himself off the ground, modeled his gliders’ wings on a careful study of storks’ wings. The streamlined shapes of dolphins suggested the shapes of airplane bodies. Alexander Graham Bell, the inventor of the telephone, was not an electrical engineer, but a professor of vocal physiology at Boston University, where he taught deaf people how to speak. The anatomy of the ear led him to construct the first microphone. Our eardrums are thin membranes which transmit sound vibrations to tiny bones in the middle ear; those bones in turn set up vibrations in the liquid-filled canals of the inner ear which our auditory nerves sense by a mechanism still unknown. In Bell’s own words:
It occurred to me that if a membrane as thin as tissue paper could control the vibrations of bones that were, compared to it, of immense size and weight, why should not a larger and thicker membrane be able to vibrate a piece of iron in front of an electromagnet…and a simple piece of iron attached to a membrane be placed at the other end of the telegraphic circuit?
Bell replaced our eardrum by a thin metal plate which he attached to a magnetized iron rod surrounded by an independently fixed coil of copper wire. The metal plate transmitted sound vibrations to the iron rod, and its vibrations in turn induced vibrating electric currents in the copper coil. A wire transmitted these to a receiving coil which set up vibrations in an iron rod attached to a metal plate. This converted the electrical vibrations back into sound vibrations. So Bell made the analogy with the ear work both ways, as transmitter and receiver.
The ancient Egyptians made paper from papyrus; later, paper was made first from linen and then from cotton …