In The Greek Interpreter, Sherlock Holmes gives two clues of his past. In addition to noting his ancestors were country squires, he also shares that art was in his blood, given his grandmother was the sister of Vernet, the French artist.
Some speculation exists as to which Vernet. Three generations of Vernets garnered patronage from both the French monarchy and Napoleon: Claude-Joseph Vernet (1714 – 1789); Antoine Charles Horace Vernet, known as Carle Vernet (1758 – 1836); and Émile Jean-Horace Vernet, known as Horace Vernet (1789 – 1863) (1). Simple mathematics suggests the most logical choice would be the youngest Vernet. For Sherlock and Mycroft’s mother to be between twenty and twenty-five at marriage, she would have to have been born between 1821-1826. Taking another twenty to twenty-five years or so for Sherlock’s grandmother to be born, means a birth date of about 1795 - 1800 or earlier, clearly putting her as a contemporary of Horace.