Even the sunrise touches night.
One hour is mine: and is no more.
We pass: the race which follows us,
Another follows: all is o’er.

In the year after he first met her, on the occasion of Richelieu’s marriage to Mademoiselle de Guise, in April, 1734, he had written:

Love not too much: and so you may
Love alway.
For were it not the better far to be
Friends for eternity
Than lovers for a day?

He had always been honest at least. If he had been still lover indeed, it might yet never have occurred to him that there could be cause for jealousy of Émilie of two-and-forty and a young guardsman of one-and-thirty.

When did that wild passion begin? Did it begin in those idle, early days of the Lunéville visit, gradually nourished by propinquity, that gay, easy life, those lovely society verses, and the tantalising fact that Saint-Lambert was a little bit in love with that stupid, lazy, self-indulgent de Boufflers? It would have been an irresistible temptation to Émilie’s cleverness and energy to win away such a man from such a woman.

But it seems more likely that she had no time for designs, that she fell head over ears in love madly, recklessly, and at once—with that utter abandon, all foolish and half pathetic, with which an old woman too often loves a young man. Was it the handsome face and cold manner and heart that attracted her? The whole eighteenth century found them attractive. Saint-Lambert had so much, too, of that particularly vague quality called taste! He liked being amused, though he found it too much trouble to be amusing himself. And here was one of the cleverest women of her day, or of any day, who could not be dull if she tried and wanted nothing better than to entertain him. She was an invigorating change from the sleepy de Boufflers, at any rate. He was not sorry, too, to obtain the cachet which would accrue to him for having robbed a Voltaire.

But whether the passion on both sides was born full-grown, dominant, and irresistible, or had slower roots in vanity and idleness, matters not. It was soon an accomplished fact. Madame du Châtelet wrote her Saint-Lambert the most mad, adoring letters on rose-coloured or sky-blue notepaper with an edge of lace. She put the letters in Madame de Boufflers’s harp in the salon. And when everyone had gone to bed, the young guardsman came and found them there. He replied of course. If he did not adore, he graciously submitted to be adored. “Come to me as soon as you are up,” wrote the deluded woman. And sometimes, secretly creeping round by the thickets of the garden, she would visit him. She hardly thought her conduct required apology. She loved him. That was enough. Or if it did, well then, for years Voltaire had been but her friend when he should have been her lover. “I loved for both.” “I had reason to complain and I forgave all.” She had tried to be satisfied with friendship: but she could not. She wrote thus to d’Argental in a letter not devoid of genuine feeling and even of pathos. She had some excuse. But she made the common mistake of thinking that an excuse and a justification are the same thing.

The Abbé Voisenon has recorded how once Madame du Châtelet, after, it may be guessed, a quarrel with Voltaire, spoke of herself as entirely alienated from him. The Abbé took down one of the eight volumes of Voltaire’s manuscript letters to her and read some aloud. All his love letters contained, says the Abbé, more epigrams against religion than madrigals for his mistress. But when the reader stopped, Émilie’s eyes were wet. She was not cured yet. A few years later, in 1749, her priestly friend tried the same experiment. She listened unmoved. She was cured indeed: and the doctor had been Saint-Lambert.

The Lunéville visit lasted from about February, 1748, until the end of April. Then Madame du Châtelet left the Court, and returned to Cirey, where she and Saint-Lambert may have spent a few blissful, uninterrupted days together. Voltaire prolonged his visit to Stanislas a short time. By May 15th he and Madame du Châtelet were both once more at Cirey en route for Paris.

During her stay at Lunéville the energetic Marquise had not only found a lover, but obtained for her bonhomme the lucrative post of the Grand Marshal of the Household to Stanislas, and a commission in the army for her son.