The Compass Rose - Map of China: Decoding the Secrets of a Vanished Cartographer - page 103

remit resulted in half a dozen voyages between 1405 and 1422 first to South-East
Asia and then into the Indian Ocean as far as the east coast of Africa. My first re-
action to this discovery was disappointment. I wanted evidence of maritime trade,
not of diplomatic missions. In fact, once I compared the routes in the Laud rutter
tothoseontheSelden map,Ifoundthat thetwoenterprises ranonthesame tracks.
This coincidence was not because the eunuch fleets opened these routes for others
tofollow;itwasbecauseeveryoneusedthesamesealanesbefore,duringandafter
the Ming dynasty. Zheng He simply sailed his treasure ships, as they were called,
where merchant seamen sailed their cargojunks. Most ofwhat is in the Laud rutter
is thus standard navigational lore, unaffected by the fact that imperial fleets sailed
the same routes.
The rutter itself begins with a long prayer that a pilot was expected to make be-
fore consulting the compass. Addressed to the Yellow Emperor, the Duke of Zhou,
six historical sages and every master who had ever successfully piloted a vessel
acrosstheocean,theprayerasksforasafeandprofitablevoyage.Therefollowsan
explanation of how to use a compass. This would not have been a dry-pivot com-
pass of the sort we are used to, in which the needle is attached to a post. Instead, it
wasafloatingcompass,whichconsistedofashallowbasinwhoserimwasmarked
with the points of the compass. The basin had first to be filled with water, then the
needleplacedonitssurfacesothatitfloated.JohnSeldenbelievedhehadacquired
just such a compass, as he notes in his will: 'a Sea Compasse of their making and
Devisione'(division).IfthisisthecompassthatisnowondisplayintheHistoryof
Science Museum along with the two Persian astrolabes Selden and Laud donated
separately (Fig. 12) then we know that Selden was mistaken. His was not a sea
compass apilotwouldtaketosea,butadry-pointcompass ofthesortageomancer
used to site a building or a grave. Sea compasses floated on water.
Pouring water into the compass is tricky, the rutter explains. 'To fill it with the
water on which the needle is set down, it is essential to use yang water and not
to use yin water. What are yin and yang water? Yang water is water that trembles
when the wind brushes it. Yin water is water that subsides when the wind falls.' I
am not confident of what that translation actually means. Could this be telling the
pilot to use salt water rather than fresh, so that it would help the needle to float?
Thenextstepis:'Laythecompassbasinlevelandorientittowardsthesouth.Then
it is necessary to set down the needle pointing to the mansion of Heaven.' Heaven
here is not all of heaven, but one of the twenty-eight lunar mansions that Chinese
astrology identifies as forming a circle above the horizon through which the moon