But though Mary thus attempted to beguile her solitude, the thought of her unjust imprisonment never ceased to prey upon her mind. Elizabeth and Cecil tried to defend themselves upon four grounds; but they were all alike weak. They said, _first_, that she was a lawful prisoner by good treaties. But as they did not mention to what treaties they alluded, Chalmers supposes they meant the same kind of treaties "which justify the Barbary Powers to detain all Christians as slaves." They said, _secondly_, that she could not be suffered to depart, till she had satisfied the wrong she had done to Elizabeth, in openly claiming the crown of England, and not making any just recompense. But the disavowal of that claim was all the recompense that was necessary; and though Mary had made the claim when married to Francis, she had expressly given it up ever since his death. They said, _thirdly_, that Elizabeth possessed a superiority over the crown of Scotland. But this antiquated notion, arising from the subservience of John Baliol to Edward I., in 1292, had long been relinquished, and had never been acknowledged in any treaty between the two nations. They said, _fourthly_, that the Queen of England was bound to attend to the petition of her subjects "in matters of blood." But though Lord and Lady Lennox had been brought forward to present a petition against Mary, it was evident that Elizabeth had no power either to grant or refuse such petition, the Queen of Scots not being one of her subjects.