Page 277 - Electrical Properties of Materials

Magnetic materials

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Quod superest, agere incipiam quo foedere fiat
naturae, lapis hic ut ferrum ducere possit,
quem Magneta vocant partio de nomine Grai,
Magnetum quia fit patriis in finibus ortus
hunc homines lapidem mirantur; ...

Hoc genus in rebus firmandumst multa prius quam
ipsius rei rationem reddere possis,
et nimium longis ambagibus est adeundum;
Lucretius De Rerum Natura

To pass on, I will begin to discuss by what law of nature it comes about that
iron can be attracted by that stone which the Greeks call magnet from the name
of its home, because it is found within the national boundaries of the Magnetes.
This stone astonishes men ...
In matters of this sort many principles have to be established before you can
give a reason for the thing itself, and you must approach by exceedingly long
and roundabout ways;

11.1 Introduction

There are some curious paradoxes in the story of magnetism that make the
topic of considerable interest. On the one hand, the lodestone was one of the
earliest known applications of science to industry—the compass for shipping;
and ferromagnetism is of even more crucial importance to industrial society
today than it was to early navigators. On the other hand, the origin of mag-
netism eluded explanation for a long time, and the theory is still not able to
account for all the experimental observations.
It is supposed that the Chinese used the compass around 2500 BC.This
may not be true, but it is quite certain that the power of lodestone to attract
iron was known to Thales of Miletos in the sixth century BC. The date is put
back another two hundred years by William Gilbert (the man of science in the
court of Queen Elizabeth the First), who wrote in 1600 that ‘by good luck the
smelters of iron or diggers of metal discovered magnetite as early as 800 BC.’
There is little doubt about the technological importance of ferromagnetism
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today. In the United Kingdom as much as 7 × 10 W of electricity are gener-
ated at times; electrical power in this quantity would be hopelessly impractical
without large quantities of expertly controlled ferromagnetic materials. Evid-
ence for the statement that the theory is not fully understood may be obtained
from any honest man who has done some work on the theory of magnetism.