1. Theo had probably referred to what the De Goncourts quoted from Denis Diderot in L’art du dix-huitième siècle, who is mentioned several times. Soon after this Theo sent the book, in which he had marked a passage from Diderot: see letter 541.

Diderot and Voltaire published their views in fictitious exchanges of letters, among them their influential Lettres sur les aveugles and Lettres philosophiques, in which they set out the ideas of the Enlightenment. In his letters to his mistress Sophie Volland, Diderot deals with more everyday events. There are many editions of the correspondence of the two authors; more than 15,000 of Voltaire’s letters have survived. See Diderot. Correspondance. Ed. Laurent Versini. 2 vols. Paris 1994-1997 and Voltaire. Correspondance. Ed. Théodor Bestermans. 13 vols. Paris 1963-1993.

2. Avenue of poplars (F 45 / JH 959

) and Autumn landscape with four trees (F 44 / JH 962

3. The English mathematician and physicist Sir Isaac Newton formulated his groundbreaking views on gravity in his Philosophiae naturalis principia mathematica (1687). In 1814 the English engineer George Stephenson built the first steam locomotive for Killingworth Colliery; fifteen years later the first passenger railway was built under his supervision.

4. The parsonage garden with figures (F 124 / JH 955

). Van Gogh also painted a watercolour of this composition: F 1234 / JH 954.

5. The only known painting of the parsonage garden from this period is Parsonage garden (F 185 / JH 484), but it is not clear whether Van Gogh is referring to it specifically here: there is no pond in it (unless by ‘that spot’ he simply means the garden).

6. The people to whom Theo showed Vincent’s work, including Portier and Serret.

7. As Van Gogh had previously promised (see letter 536), he meant to return Theo’s copy of Blanc’s Les artistes de mon temps.

8. This is the nineteenth-century Bible in Still life with Bible (F 117 / JH 946

); it is now in the Van Gogh Museum collection (s8 V/1962). See cat. Amsterdam 1999, pp. 218-225, with illustration. In the end the paintings, the Bible and Les artistes de mon temps were not sent (see letters 542 and 543).

a. Means: ‘doorschijnende lagen, vernisverven’ (transparent layers, varnishes).

9. Jan Vermeer of Delft, View of Delft, c. 1660-1661 (The Hague, Royal Cabinet of Paintings Mauritshuis). Ill. 2162

10. At this time Hendrik Johannes Haverman, The flight, 1883 (present whereabouts unknown) was hanging in the Rijksmuseum. Ill. 923

. Vincent assumed that his brother must remember the work from his visit to the museum in August.

11. Van Gogh had been to the Fodor Museum in Amsterdam at the beginning of October: see letter 534. Among these rather ‘smoothed-out’ works that are cracked is The Greek exiles by Ary Scheffer (with thanks to Gusta Reichwein).

12. In his Histoire des artistes vivants français et étrangers Silvestre said of Delacroix: ‘He worries terribly about his pictures and takes great care to prevent them deteriorating; he treats them like sick children, bathing them in oil, agonizing over vagaries in the atmosphere and about the dangers involved in travel, he carries out all sorts of experiments on the quality of paints and canvas, he shudders at the thought that they might be destroyed, redoubling his working activities and relentlessly increasing his subjects’ (Il se donne mille chagrins et mille soins afin de prévenir l’altération de ses tableaux; il les traite comme des enfants malades, les fait baigner dans l’huile, se tourmente pour eux des caprices de l’atmosphère, du hasard des voyages; fait toute sorte d’expériences sur la qualité des couleurs et des toiles, frémit l’idée de la destruction, redouble d’activité au travail, et multiplie ses sujets avec acharnement) (see Silvestre, Histoire, p. 68).

13. Theo sent Léon Augustin Lhermitte’s prints in the series ‘Les mois rustiques’ which appeared in Le Monde Illustré at the end of each month. Vincent, who is asking here about the October print, found it for himself some time later (see letter 545).