The coronation of 1689 was unique, since it is the only time in English history that joint sovereigns have been crowned.  This meant that Mary II required Crown Jewels equal to that of her husband, William III. This orb was created by Robert Viner, a relative of the Royal Goldsmith Robert Viner who had prepared the regalia for Charles II. 

The orb symbolises the Christian world with its cross mounted on a globe, and its bands of jewels and pearls dividing it up to represent the three continents known in medieval Europe.  Since Roman and Byzantine times, orbs have also served as symbols of imperial power.