Cathcart had been a staff officer with Wellington in the Napoleonic Wars, and rose in rank to become commander of British forces in North America from June 1845 to May 1847. He was also appointed as Administrator then Governor General for the same period, uniting for the first time the highest Civil and military offices. The appointment of this military officer as Governor General was due to heightened tensions with the United States over the Oregon boundary dispute. Cathcart was deeply interested in the natural sciences, but ignorant of constitutional practice, and hence an unusual choice for Governor General. He refused to become involved in the day-to-day government of the conservative ministry of William Draper, thereby indirectly emphasising the need for responsible government. His primary focus was on redrafting the Militia Act of 1846. The signing of the Oregon Boundary Treaty in 1846 made him dispensable. James Bruce, 8th Earl of Elgin (1847–1854) Elgin's second wife, Lady Mary Louisa Lambton, was the daughter of Lord Durham and niece of Lord Grey, making him an ideal compromise figure to introduce responsible government. On his arrival, the Reform Party won a decisive victory at the polls. Elgin invited LaFontaine to form the new government, the first time a Governor General requested cabinet formation on the basis of party. The party character of the ministry meant that the elected premier – and no longer the governor – would be the head of the government. The Governor General would become a more symbolic figure. The elected Premier in the Legislative Assembly would now become responsible for local administration and legislation. It also deprived the Governor of patronage appointments to the civil service, which had been the basis of Metcalfe's policy. The test of responsible government came in 1849, when the Baldwin–Lafontaine government passed the Rebellion Losses Bill, compensating French Canadians for losses suffered during the Rebellions of 1837. Lord Elgin granted royal assent to the bill despite heated Tory opposition and his own personal misgivings, sparking riots in Montreal, during which Elgin himself was assaulted by an English-speaking Orange Order mob and the Parliament buildings were burned down. Edmund Walker Head, 8th Baronet (1854–1861) The appointment of Walker Head (a cousin of Francis Bond Head, whose inept governance of Upper Canada led to the Rebellion of 1837) is ironic. Some have argued that the Colonial Office meant to appoint Walker Head to be Lt.