A preservative against the principles, and practices of the dissenters : Wherein; I. The authority of bishops is vindicated, and their mission clearly proved from the Holy Scriptures, fathers and councils. II. Demonstrating, that the fanatical conventicles of Great Britain and Ireland are no true constituted Churches of Christ. From whence it naturally follows, that the members of such a community are no Christians, in a letter to a gentleman, formerly a dissenter, but now a member of the Church of England. By William Cowan, gent. To which is added, a short explanation of the festivals of the Church of England.