The intangible Universe - Electromagnetism and fields

4 The intangible Universe

4.1 Electromagnetism and fields

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When Newton wrote about 'The System of the World' in Part 3 of Principia, the only forces he could discuss in any detail were the contact forces that arose when one object touched another, and gravity, which acted at a distance. Even so, Newton thought that there were other forces at work in the world, and hoped they might eventually be brought within his overall scheme just as gravity had been. In fact, Newton wrote:

'I wish we could derive the rest of the phenomena of Nature by the same kind of reasoning from mechanical principles, for I am induced by many reasons to suspect that they may all depend upon certain forces by which the particles of the bodies, by some causes hitherto unknown, are either mutually impelled towards one another, and cohere in regular figures, or are repelled and recede from one another.'
Isaac Newton (1686), Principia.

Amongst the phenomena familiar to Newton, but which he could not treat mathematically, were those of electricity and magnetism, both of which had been known since antiquity

Figure 1.16 Examples of electric and magnetic forces
figure 1.16a
^{Click here for larger image (9.28kb)} ^{Examples of electric and magnetic forces. The ancient Greeks were aware that when samples of amber, which they called
(electron)
were rubbed with wool or fur they acquired the ability to attract light objects such as feathers. They were also aware that the substance we now call lodestone, which could be found in northern Greece in the area known as Magnesia, had the ability to attract pieces of iron.}
figure 1.16b
^{Click here for larger image (9.43kb)}
One of the key concepts that Newton lacked, but which eventually proved to be crucial to the quantification of both electricity and magnetism was that of electric charge. This was originally viewed as something like a fluid that could be passed from one object to another, but is now seen, rather like mass, as a fundamental attribute of matter.
Continue on to Electromagnetism and fields, part 2 of 4