Of the passions with which the mind of man is agitated, it may be observed, that they naturally hasten towards their own extinction, by inciting and quickening the attainment of their objects. Thus fear urges our flight and desire animates our progress; and if there are some which perhaps may be indulged till they outgrow the good appropriated to their satisfaction, as it is frequently observed of avarice and ambition, yet their immediate tendency is to some means of happiness really existing, and generally within the prospect . . . . But for sorrow there is no remedy provided by nature; it is often occasioned by accidents irreparable, and dwells on objects that have lost or changed their existence; it requires what it cannot hope, that the laws of the universe should be repealed; that the dead should return, or the past should be recalled.