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Action at a Distance

Another perplexing problem for turn-of-the-Century scientists was the issue of whether two objects had to ``touch'' in order to exert forces on each other. The car's wheels touch the road, the crane lifts the concrete block by a cable attached to it and the arrow's flight is slowed by air molecules rubbing against it; so how exactly is the Earth's gravitational force transmitted to the cannonball?^16.5

Physicists might have been willing to live with the idea that ``gravity is weird,'' were it not for the fact that other types of forces also appeared to act ``at a distance'' without any strings attached (as it were) - namely, the electrical and magnetic forces whose simplest properties had been know for millenia but whose detailed behaviour was only beginning to be understood empirically in the late 19$^{\rm th}$ Century. An amber rod rubbed with rabbit fur attracts or repels bits of lint or paper even when separated by hard vacuum; a lodestone's alignment will seek magnetic North wherever it is carried [an important practical property!] except at the North Pole, where we seldom need to go. How does the North Pole ``touch'' the magnetic compass needle? What is going on here? How can things act on each other without touching? Weird.

There are other examples of ``weird science'' that kept cropping up around the turn of the Century; I will append some more to this Chapter as we go on, but for now it's time to get on with ELECTRICITY AND MAGNETISM.