The Hartlib Circle were a far-reaching group of correspondents linked to Hartlib, an . They included Sir Cheney Culpeper and Benjamin Worsley who were interested, among other matters, in alchemy. Worsley in 1646 was experimenting on saltpetre manufacture, and Charles Webster in the "Oxford Dictionary of National Biography" argues that he was the "prime mover" of the Invisible College at this point: a network with aims and views close to those of the Hartlib Circle with which it overlapped. Margery Purver concludes that the 1647 reference of "invisible college" was to the group around Hartlib concerned to lobby Parliament in favour of an "Office of Address" or centralised communication centre for the exchange of information. Maddison suggests that the "Invisible College" might have comprised Worsley, John Dury and others with Boyle, who were interested in profiting from science (and possibly involving George Starkey).