This optical instrument serves as one of Proust's principal metaphors for social evolution, such as the tremendous changes in French society resulting from traumatic events like the Dreyfus Affair and World War I:
It was true that the social kaleidoscope was in the act of turning and . . . the Dreyfus case was shortly to relegate the Jews to the lowest rung of the social ladder.
The Guermantes Way 3: 252
Il est vrai que le kaléidoscope social était en train de tourner et que l'affaire Dreyfus allait précipiter les Juifs au dernier rang de l'échelle sociale.
Le Côté de Guermantes 2: 487
In July 1895, Marcel accompanied his mother to the Oranienhof, a German health resort located on the Nahe River in Kreuznach, an old picturesque town in Rhineland-Palatinate, known for its mineral springs. He took the waters with his mother in the morning and enjoyed late-evening boating excursions on the river, even though mosquitoes swarmed around him. It is possible that during this stay Marcel began writing some scenes for his first attempted novel, known as Jean Santeuil.
In June, Robert de Billy had married Jeanne Mirabaud, daughter of wealthy financier Paul Mirabaud, Director of the Banque de France. Billy and his wife, enjoying an extended honeymoon, were traveling near Kreuznach and stopped by for a brief visit. Proust, bored because he was so far from his friends, was delighted at their arrival. Mme Proust greeted the new Mme de Billy with her "customary kindness." Billy, well on his way to achieving his professional and personal goals, seemed radiantly happy, his future assured.
Billy writes of the visit in his memoirs, Lettres et conversations: "We spoke of Germany where I had spent a year and Marcel, who was interested in my recollections, said that I must write them down and made it an obligation for me to do so. After lunch, he said to me: 'Your wife will have a rest and you, you're going to write whatever you like'." After two hours of work, he came to see what I had written." Because Proust knew how much "I admired Flaubert and Hugo," he encouraged me to persist "but advised me to be aware of epithets."
In August 1897, Marcel and his mother returned to the Oranienhof for several weeks because she believed the treatments benefitted her health. Marcel disliked this spa and decided to devote much of his time to reading works that he hoped would inspire his writing. He sent a quick note to Lucien Daudet, asking which authors or books he should add to his list. He especially sought advice about British and Russian writers whose works he had heard praised. He peppered Lucien with questions; who wrote The Brothers Karamazov? "And has Boswelle's [sic] Life of Johnston [sic] been translated?" And finally, "What's the best of Dickens (I haven't read anything)?" Over the course of his life Proust showed a preference, among foreign authors, for British and Russian novelists. As far as we know, Proust never read Boswell's biography, which had not yet been translated into French.
See Yacht for more information about Proust and Robert de Billy.