Seeing

Just recently, I read a rather fine new scientific biography: Boltzmann's Atom, by David Lindley (formerly an editor at Nature); the subtitle is ''The great debate that launched a revolution in physics". The book
takes us back more than a hundred years to a time when the existence of atoms and molecules was still hotly disputed. Ludwig Boltzmann in Austria and James Clerk Maxwell in Britain (although they never met) were jointly polishing the kinetic theory of gases, which presupposes the existence of rapidly moving molecules; and yet sceptics like Wilhelm Ostwald and Ernst Mach denied mat molecules, or atoms, existed. The wonderful work of Jean Perrin and Alben Einstein on Brownian motion (that's one of Einstein's less well known theoretical achievements) early in the twentieth century brought most sceptics round, but Mach, the positivist philosopher, was implacable. No one had ever seen an atom, he expostulated, and what you can't see doesn't exist... or, at least. there is a very strong presumption against such existence. The mere fact that kinetic theory was beautifully consistent with observation entirely failed to impress him. The end result of his unrelenting and public hostility to
Boltzmann was Bolrzmann's suicide in 1906. 

There were other later scientists, more famous than Mach (who formed his own coterie of philosophers around him in Vienna), who shared Mach's hostility to theory and wished to devote themselves to empirical observation alone. Roben Pohl in Gottingen who studied color centers in ionic crystals. and Percy Bridgman at Harvard. who pioneered research in high-pressure physics, were likewise passionate empiricists.

Most scientists recognize the essential tole of theoretical models in the gradual teasing out of scientific truth, but still,  most of them want to see. That is why microscopy has proved to be so crucial a skill in the evolution of materials science. The restless skittering of tiny suspended particles under bombardment by moving molecules in the suspending liquid could be seen, and measured, and that was the essential starting-point in Perrin and Einstein's work on Brownian motion. Not long after their researches were completed, in 1911, C.T:R. Wilson in Cambridge invented the cloud-chamber, which allowed the trajectories of charged subatomic particles to be seen. Rutherford himself declared that though the cloud-chamber was not logically essential to his interpretation of atomic structure, yet its invention carried conviction where people had been sceptics before. The electron microscope in the 1950s convinced metallurgists of the existence of Guinier-Preston zones (which had up to then only been detected by X-ray diffraction) and a little later, of the existence of dislocations (which were theoreticians' constructs), and later still, the scanning tunneling microscope permitted Donald Eigler
at IBM (Q move individual atoms to form predetermined patterns on a surface. That was the Ultima Thule of microscopy... an instrument that allowed atoms to be moved and at the same time to provide an image
of those atoms.

Psychologically, we need images of very small things to persuade us of their function and, indeed, of their very existence. That way, temperamental empiricists and deep theoreticians can dwell amicably together.