I have learned from Michael Glover that once an officer reached the level of full colonel that periodic automatic brevet promotions would take him through the various levels of general ranks (unless his mistakes were too noticeable). From Howie Muir (chapter 4 of Muir, Burnham, Muir and McGuigan) and others I know that both rank and seniority were used in some way to determine a generals‘ assignments and positions. However, I am still not sure why Lieutenant-General George Cockburn had to leave Lieutenant-General John Stuart’s staff in Sicily in 1810 because of his unexpected promotion to lieutenant-general; he had been on the Sicilian staff less than a year when he had to leave. He wrote: ‘Promotion, which in all other professions is an advantage, is often the contrary to the higher ranks of the army navy. Mine to Lieutenant-General, removed me from the Sicilian Staff’
Three questions: Why did Cockburn have to leave the staff at Sicily (his journal indicated that he did not want to leave)? What determined when a general received an automatic promotion? Did these automatic promotions of generals require some sort of purchase payment?