Development of the Compass

Having established the sophistication of Olmec lapidaries in working magnetic minerals, we now consider what information about the properties of lodestone may have been available to the Olmec. A first step in the discovery of the compass is observation of the attractive properties of lodestone. The term lodestone is usually applied to an iron ore mineral that attracts bits of iron or other lodestones; I will use it to mean any iron ore mineral with a geomagnetic remanent magnetization. I have tried polishing magnetite and found that the dust and fine grains will cling to this lodestone. Thus, in polishing iron ore mirrors the Olmec lapidary might well have discovered their attractive properties. If the Olmec preserved meteoritic iron, they could also have observed the lodestone's attraction for iron.

Also probable as first or successive steps in the development of the compass are the critical discoveries of magnetic polarity and the geomagnetically orienting properties of lodestone. For example, by suspending a lodestone from a filament isolated from air currents or by floating it on wood in water or directly on liquid mercury, one might discover that the lodestone will consistently orient itself in a particular direction. This "zeroth-order compass" could be devised to indicate any desired direction-- for example, an astronomical direction, one of the cardinal points. In calling the lodestone a zeroth-order compass I refer to the use of its self-orienting properties with no knowledge of its tendency to point north-south. In this sense, it is not a true compass.

The magnetic polarity of needles or bars of magnetic mineral might be discovered by noting the response of two stones to each other or seeing the magnetic field pattern in magnetite dust or iron filings. Almost 2000 years ago, the Chinese learned that the directive property of lodestone could be transferred to a piece of iron. Since the Olmec apparently did not possess iron, we must concentrate on the uses of lodestone. At this level of understanding, one might be totally unaware of the property of magnetic polarity or the fact that the earth acts like a large magnet with the north and south poles corresponding roughly to celestial north and south. The geomagnetic field was a much later discovery in China and the Western World.

The next step in awareness of the properties of lodestone is the discovery of the true orientability of the poles in the approximate north and south cardinal directions of the earth. With this step the lodestone becomes a first-order compass. A long magnetized bar or needle has a tendency to have its magnetic poles at the ends, so that it orients itself roughly northsouth. This tendency is independent of the knowledge or purpose of the artisan (for instance, whether the sample was purposely cut from a north-south deposit of native mineral). The user of a first-order compass would probably calibrate or offset it to orient itself to the north-south direction and would be unaware of the geomagnetic deviation (the fact that a compass points toward geomagnetic north and not true north). At this time also, polarity would become apparent to the extent that one end of the compass would always point in one direction (either north or south). This question has been discussed in the Chinese context by Needham (1, pp. 236, 333).

The development of what I call a second-order compass involves a good understanding of magnetic polarity and awareness of the geomagnetic deviation and the fact that this deviation changes for different places on the earth. This is a very sophisticated discovery and is necessary for compass navigation.

One further step involves the discovery that over generations, the magnetic deviation changes with time as well as place. As far as we know, the appreciation of this secular variation is a relatively modern discovery (17th century). Even today, the physical causes of the changes in the geomagnetic field, and even its origin, are not well understood.

The discovery of the attractive properties of lodestone and the early history of the compass in China and the Western World are well treated by Needham (1, pp. 229-334). The properties of the lodestone were apparently known to the Greeks; the earliest observations were attributed to Thales (6th century B.C.) (1, p. 231). A comparable antiquity is indicated in China, perhaps not as early as Thales, but definite references exist for the 3rd century B.C. (1, p. 232). According to Needham, the approximate north-south orienting ability of a bar of lodestone was discovered by the Han Dynasty Chinese no later than the 1st century A.D. and perhaps as early as the 2nd century B.C. (1, p. 333).

By the late Thang period (+8th or +9th century) the declination, as well as the polarity, of the magnet, had been discovered, antedating European knowledge of the declination by some six centuries. The Chinese were theorizing about the declination before Europe knew even of the polarity (end of the + 12th century).

This discovery was developed into what was known as the "south-pointing spoon," which will be discussed in greater detail later.

Once the orientability of lodestone became known, what was the compass used for? In China it was used first in divination and geomancy and only much later for navigation (1, p. 239).

That so fundamental an instrument did in fact spread so slowly is not difficult to understand once we realize that its original discovery took place in connection with the divination process of imperial magicians; and that since it developed in an agrarian-terrestrial rather than in a primarily maritime civilisation, its use was for centuries limited to a specific Chinese pseudoscience, namely Taoist geomancy, the minutiae of which were carried to a high level of refinement. The adoption of the compass by Chinese sailors was probably long retarded by the fact that all through the Middle Ages river and canal traffic predominated over ocean voyages.

... Of all the forms of divination, geomancy was perhaps that which become most deeply rooted in Chinese culture throughout the traditional period.... The term geomancy has other meanings in other civilisations, but for the Chinese it meant the "art of adapting the residences of the living and the tombs of the dead so as to cooperate and harmonize with the local currents of the cosmic breath." Known as the science of "winds and waters" (feng shui) [15, 16] it did not mean merely the winds of everyday life, but rather the chhi or pneuma of the earth circulating through the veins and vessels of the earthly macrocosm. The waters, too, were not only the visible streams and rivers but also those passing to and fro out of sight, removing impurities, depositing minerals, and like the chhi affecting for good or evil, the houses and families of the living, as also the descendents of those who lay in the tombs. The history of the magnetic compass is only understandable in the context of this system of ideas, for this was the matrix in which it was generated.

This discussion of the development and use of the compass in China is quite relevant to a comparative argument for the possible use of a first-order compass by the Early Formative Olmec.