the globe itself , the surface of which is meticulously engraved with a map of the world with the principal cities indicated by brilliant diamonds embedded within gold collets , rotates mechanically on an axis controlled by a small clock-movement , by g. moser , signed , which is concealed in the base , and is girdled by a fixed gold belt enameled opalescent oyster along a reserved path in champleve technique over a moire guillochage with painted roman numerals in pale sepia enamel serving as the dial of the clock , and a single triangular pigeon-blood burma ruby of about five carats set into the surface of the orb , pointing the hour .