Voltaire dedicated his Metaphysics to Émilie and sent a copy to her with this verse:

Of the author of Metaphysics, beware:
He’s on his knees before you.
He ought to be burnt in the town square
But he only burns for you.

While Voltaire is in Holland in early 1737, Émilie is beside herself about this very work. She writes to their friend d’Argental:

In his letter of the 8th he sends me a copy of his letter to the Crown Prince of Prussia, that is all very well and all very prudent, but look what I find: ‘I shall be bold enough to send Your Royal Highness a manuscript that I would only show to someone with a mind as free of prejudices as your own, and who, amongst all the praises one may bestow, are worthy of boundless trust.’

I know this manuscript: it’s his Metaphysics, so replete with reason that it would send him to the stake, a book that’s a thousand times more dangerous—and certainly more actionable—than La Pucelle [Voltaire’s risqué poem on Joan of Arc]. Imagine how it shook me; I still haven’t got over my astonishment—or, may I tell you, my anger. I sent him a furious letter; but it will take so long on the way that the manuscript may have gone off before it gets to him, or at least he’ll be able to claim it has—because sometimes we are carried away, and the demon called reputation (his view of which I do not share) never leaves us alone.

I must tell you I couldn’t help lamenting over my fate, when I saw how little the tranquillity of my life must mean to him. In future I shall be always fighting against him for his own good, but without being able to save him. In his absence, I’ll be either trembling for him or lamenting over his faults. But in the end, that is my destiny, and it’s dearer to me than the happiest of futures. You must help me to parry this latest blow, if it can be done, because sooner or later his imprudence will destroy him for ever. The Crown Prince can no more keep this particular secret than he can himself.