This is our planet's ideogram, the sign for the
earth, or the planet
called Tellus. It has
been found on a Cyprian coin from
around 500 B.C. It is similar to the so-called orb, used by rulers during the Middle Ages
to symbolize their control over a part of the earth's surface. See
in Group 23.
Compare with the structurally similar graph representing our nearest planetary neighbour in space, , Venus, and with the astrological sign for the element of earth, .
Compare also with the sign for earth = ground, .
In alchemy and early chemistry the sign was used for antimony, an element similar to arsenic (see in Group 5), blue-white to silver-white, which was once used as a medicament and for bronzing, for alloys, etc. In alchemy this sign has also been used for cinnabar, i.e. red mercury sulphide, an important colouring substance.
Today it is used on maps to indicate a chapel, rectory, etc.
A "filled-in" version of this sign, , is used in military contexts to denote the officer in command. The ordinary can also mean commanding officer.