Two lectures on comets : read in the chapel of Harvard-College, in Cambridge, New England, in April 1759. On occasion of the comet which appear'd in that month. With an appendix, concerning the revolutions of that comet, and of some others. By John Winthrop, Esq. Hollisian Professor of the Mathematics and Philosophy at Cambridge. Published by the general desire of the hearers. - Winthrop, John, (Printed and sold by Green & Russell, at their printing-office in Queen-Street. Sold also by D. Henchman, at his shop in Cornhill,, 1759)