Brown writes of the visible Church in the context of making it plain that "it would be unlawful on account of the scandals of the members of the Church or on account of the neglected Ecclesiastical discipline, or discipline not faithfully enough administered, to separate from the Church". This is a vital truth to remember. Christ never instructed the faithful to separate from those of the Seven Churches of Asia where discipline was not being carried out faithfully.
Brown wrote originally in Latin but the work has now been fully translated and available at
http://www.cpjournal.com/wp-content/uploads/2007/06/cpj2-intranslatione.pdf