Online absentee bidding in Heritage's Rare Books & Historical Manuscripts auction will close tomorrow night (February 10) at 10pm.
The sale, to be held in Beverly Hills, California, will then take place between February 11 and 12.
Star collectibles in the sale include a signed photograph of Albert Einstein, believed to be addressed to his mentor Chaim Weizman, the then-president of the World Zionist Organisation.
Bids on the photo - depicting Einstein, handsomely dressed in his forties - currently stand at $6,500.
Another stand-out is a letter signed by George Washington and franked "President U.S.", dated October 17, 1796.
Written to Edward Carrington, Washington sends his regrets at having not received Carrington's recommendation for Surveyor General before nominating another candidate.
Bids on the letter currently stand at $27,500.
Books for sale include a number of exceptionally important historical works - among them, an early print of a Fourth Folio of Shakespeare's plays, Enid Blyton, and a first edition of Darwin's On the Origin of Species.
The latter is auctioning with a reserve of $110,000.
Also appearing is a more recent literary classic: a signed copy of Harry Potter and the Philosopher's Stone, with an estimate of $15,000. Elsewhere, a signed copy is available to collectors.
Absentee bidding for live sessions with no floor bidding will end two hours prior to the opening of the live auction for that lot.