Sentence:  [I]t seemed to create a sort of material link between the Princess and himself, and at the end of three months it almost appeared to him, not that the exquisite book was an intended present from his own hand, but that it had been placed in that hand by the most remarkable woman in Europe.... [T]he superior piece of work he had done after seeing her last, in the immediate heat of his emotion, turned into a kind of proof and <WSD>gage</WSD>, as if a ghost, in vanishing from sight, had left a palpable relic. 
Meaning of the word marked with <WSD> tags:  Something valuable deposited as a guarantee or pledge; security, ransom.