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The Body Electric
his surprise, oysters in an aquarium with constant light, temperature,
and water level still opened and closed their shells in time with their
compatriots at the beach. To find out why, Brown flew oysters in a
lightproof box from New Haven to his lab, in Evanston, Illinois. At first
they kept time with Connecticut oysters, then in a few weeks gradually
shifted to the tide pattern Evanston would have had if it had been on a
seacoast. The oysters not only knew they'd been taken 1,000 miles west-
ward, they also suffered from jet lag!
In his search for a creature whose response to magnetic fields might
tell him more about biocycles, Brown settled upon the mud snail
Nassarius, at home in the intertidal zone anywhere in the world. In his
lab he placed the snails under uniform illumination in a box with an exit
facing magnetic south. When they left the enclosure in early morning,
they turned west. When leaving at noon, they turned east, but took a
westerly course again in early evening. Furthermore, at new and full
moon, the snails' paths veered to the west, while at the quarters they
tended more eastward than at other times.
Brown's precise data from this and many other experiments showed
that Nassarius had two clocks, one on solar time and one on lunar, and
subsequent work with magnets told something about how the time-
pieces ran. The earth's magnetic field averaged 0.17 gauss in Evanston.
When Brown put a 1.5 gauss permanent magnet facing north-south
underneath the snails' doorways to augment the natural field, the ani-
mals made sharper turns, but their direction wasn't affected. Turning
either the magnet or the enclosure through various angles made the
snails change course a specific number of degrees. Brown concluded: "It
seemed as if the snails possessed two directional antennae for detecting
the magnetic field direction, and that these were turning, one with a
solar day rhythm and the other with a lunar day one." This crucial
experiment not only showed the dependence of biocycles on the earth's
magnetic field, it also demonstrated the subtlety of the link. No longer
could we expect changes in the magnetic environment to be as obvious
in their effects on life as changes in oxygen levels, food supply, or tem-
perature.
The niceties of the earth's electromagnetic field itself became better
known as Brown's work progressed. Far from a static, simple magnetic
field like that around a uniform bar of magnetized iron, the earth's field
has turned out to have many components, each full of quirks.
At the end of the nineteenth century, geophysicists found that the
earth's magnetic field varied as the moon revolved around it. In the same
period, anthropologists were learning that most preliterate cultures reck-