The bulk of their authorship was prodigious, even though most of it was in the form of pamphlets or booklets, for it amounted in the case of Increase to about one hundred and fifty titles, and in the case of Cotton to nearly four hundred. But they are chiefly remembered for three books: "An Essay for the recording of Illustrious Providences," by the elder; and "The Wonders of the Invisible World" and the "Magnalia Christi Americana: Or the Ecclesiastical History of New-England," by the younger. The first two of these are unintended explanations to the twentieth-century reader as to how a whole community could ever have been swept into the Salem witchcraft excesses of 1692. Any educated man who should advance the theories to-day which were soberly expounded by these two really learned men would be held up to scorn and very possibly be made subject of a sanity investigation. Yet two hundred years ago the world was ignorant of the commonplaces of science. Popular superstition therefore ran riot; and the belief that God would interpose in the affairs of daily individual life, and that a personal devil was walking up and down the earth seeking whom he might devour, added to the confusion. Medicine in those days was hardly a science even in the broadest sense of the word. Physicians depended for honest effects on a few simple herb remedies and on powerful emetics and the letting of blood. The populace believed in curatives which still are resorted to only by children and the most ignorant of grown-ups--like anointing implements with which they had been injured, in order to heal cuts and bruises, or like being touched by the monarch as a remedy for scrofula, the "king's evil." Sir Kenelm Digby, a well-known subject of Charles II, reported that he overcame a persistent illness by having the fumes of camomile poured into his ear. The same sort of speculation prevailed in all the other sciences; and side by side with it superstition flourished. Between 1560 and 1600 in the little kingdom of Scotland, which had a population no larger than that of Massachusetts to-day, there were eight thousand executions for witchcraft,--an average of nearly four a week; and James I, who was Scotland's gift to England, was the author of a work on demonology. What the New Englanders, and among them the Mathers, believed was, therefore, not unusual at the time. In fact the Mathers were both somewhat less credulous than their fellows, but they only substituted one superstition for another. Their way of casting off the old and vulgar beliefs which were pagan in origin was to contend that these vain and foolish ideas were put into Christian minds by Satan and his emissaries. Said Increase Mather in his "Illustrious Providences":