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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.