A letter to George Heathcote, Esq; on his late resignation, as alderman of the City of London. Shewing the ill consequences of despairing of the Common-wealth, or retiring from public business, more especially in times of vice and corruption. With some cursory observations on the late management of the navy. To which is added, a copy of Mr. Heathcote's letter to the lord-mayor of London, and of the resolutions of that city in consequence of his resignation