One graceless hanger-on turned back as he was leaving him one day. ‘M. Diderot, do you know any natural history?’ ‘Well,’ says Diderot, ‘enough to tell a pigeon from a humming-bird.’ ‘Have you ever heard of the _Formica leo_? It is a very busy little creature; it burrows a hole in the earth like a funnel, covers the surface with a fine sand, attracts a number of stupid insects to it, takes them, sucks them dry, and says, “M. Diderot, I have the honour to wish you a very good morning.”’ It may be said of Diderot that he could love, but not respect; and that is the inevitable attitude one takes towards himself. In 1755, during his work at the Encyclopædia and for those innumerable idle persons who had much better have worked for themselves, poor Nanette went on a second fatal visit to Langres and gave her husband the opportunity of falling in love with Mademoiselle Volland, and starting a memorable correspondence. Sophie Volland was a rather elderly young lady, with spectacles, and a good deal of real cleverness and erudition. Whether Diderot, who was now a man of forty-two, was ever literally in love with her, or whether he was ‘less than lover but more than friend,’ remains uncertain. His letters to her are warmly interesting, frank, natural, spontaneous, with many passages of exquisite beauty and thoughtfulness. There is but one fault--that fatal fault without which Diderot would not have been Diderot at all but some loftier man--his irrepressible indecency. He had much to tell Mademoiselle. The words seem to trip over each other in his anxiety to show her all he had done and felt. He was now famous. The Encyclopædia had thrown open to him, cutler’s son though he was, the doors of the _salons_; a great quarrel he had with Eousseau in 1757--the dingy details of which there is neither interest nor profit in recalling--made him the talk of the _cafés_. But this loud, explosive Denis was scarcely a social light. He said himself that he only liked company in which he could say anything. And what Diderot meant by _anything_ was considered indecorous even in that freest of all free-spoken ages. Good old Madame Geoffrin lost her patience with him, not only for his licence, but for talking so movingly about duty and neglecting all his own. _She_ was not going to ignore his Mademoiselle Volland. She treated him ‘like a beast,’ he said, and advised his wife to do the same. As for Madame Necker--‘qui raffole de moi,’ said the complacent Denis himself--she too ‘judged great men by their conduct and not by their talents,’ which was very awkward indeed for a Diderot.