Occasional essays on the yellow fever : containing a number of remarkable relative facts, as well as some encouraging ideas, that those cities of America, which for more than ninety successive years, had been generally preserved from the dreadful evil, may by the divine blessing on wise and prudent measures, experience in future, a similar preservation from the dire calamities of a mortal pestilence. : Addressed to those who have not forgotten what has happened, within a few years, among their friends and fellow citizens. / By a Philadelphian.