1. In the first place we need not travel far, either in regard of time or place, to find Precedents of such as have undergone no small censures and subsannations for vindicating Truth, and labouring the advancement of it, though against common and deep-rooted Opinion. So ill entertainment new Inventors and Inventions have always found amongst the present Masters of several Professions, and those that made the World believe, that they alone had gained the Monopoly of all Learning. Our learned Countryman Doctor _Hackwell_ in his Preface to his Apology, hath sufficiently proved this particular: whose profound Piece of proving no decay in Nature (a truth now sufficiently known, and assented to) found no small opposition, both from the Learned in Theology, and other persons, and underwent many sharp censures, until men had more considerately weighed the strength and cogency of his Arguments, which carry sufficient evidence to confute rational persons. Our learned and most industrious Anatomist Dr. _Harvey_, who (notwithstanding the late Cavils of some) first found forth and evidenced to the World that rare and profitable discovery of the Circulation of the Blood, did undergo the like Fate: who for eighteen or twenty years together did groan under the heavy censure of all the Galenists and expert Anatomists almost in _Europe_, and was railed upon, and bitterly written against, not only by such as _Alexander Rosse_ and Dr. _Primrose_, but by _Riolanus_ and others, and not forborn by that famous Physician of _Roterodam_, _Zacharias Sylvius_, who ingenuously confesseth thus much: _Primum mihi inventum hoc non placuit, quod & voce & scripto publicè testatus sum; sed dum postea ei resultando & explodendo vehementiùs incumbo, refutor & ipse & explodor: adeò sunt rationes ejus non persuadentes, sed cogentes: diligenter omnes examinavi, & in vivis aliquot canibus eum in finem à me dissectis, verissimum comperi_. Which was a most candid and free retractation and confession of his own errours, and may be proposed as an example to all rash and unadvised Censurers. Neither could this most clear and evidential Verity (which falls under ocular Demonstration and manifest Experiments) find countenance in the World, until that _Wallæus_, _Plempius_, and divers other judicious and accurate Anatomists, had sound the truth of _Harvey_’s opinion, by their own tryals and ocular inspection: so difficult it is to overthrow an old radicated opinion. For I have known some years ago, that a person for owning or maintaining the Circulation of the blood, should have been censured and derided, as much by other Physicians, as one should be now for denying the same: so hard it is to root out an opinion (though never so false and groundless) if once setled in the brains of many, and hath had a long current of continued reputation and belief. And it is much more to consider the ignorance, stupidity, and perversness of those,