Plus ultra, or, The progress and advancement of knowledge since the days of Aristotle in an account of some of the most remarkable late improvements of practical, useful learning, to encourage philosophical endeavours : occasioned by a conference with one of the notional way / by Jos. Glanvill.

CHAP. IX. The Credit of Optick-Glasses vindi∣cated, against a Disputing Man, who is afraid to believe his Eyes against Aristotle. (Book 9)

THus, Sir, I have performed the first part of my promise, by shewing what Advantages the latter Ages, and par∣ticularly the ROYAL SOCIETY, have for deep search into things both by ARTS and INSTRVMENTS new∣ly invented or improved, above those en∣joy'd by Aristotle and the Ancients.

To my Discourse about the Dioptrick Tubes, the Telescope and Microscope, the Reverend Disputer replied, [That our Glasses were all deceitful and fallacious.] Which Answer minds me of the good Wo∣man, who when her Husband urged in an occasion of difference, [I saw it, and shall I not believe my own Eyes?] Replied brisk∣ly, Will you believe your own Eyes, before your own dear Wife? And it

seems this Gentleman thinks it unreasonable we should believe ours, before his own dear Aristotle.

For an assurance of the credit of those Glasses, I told him he might try them up∣on objects near, and easily visible by the un∣assisted sight; and if he made the tryal, he would find they altered the objects in nothing but their proportions, which are represented larger for the advantage of vision in things small and remote; and we have all the like reasons to distrust our Eyes, as these Glasses (for their informations are the same in all things, but the mentioned difference) and there is no man so much a fool, as not to make allowances for that. Never was any yet so grosly deceived by the Micro∣scope, as to be perswaded that a Flea is as big as a Lobster; nor did the Telescope ever make any one believe that the Moon was at the end of his Tube: But if the former re∣presents that little Creature as bristled and Ja••ar'd, and the other makes the Planet mountanous and uneven, we have no reason to believe but that their reports are sincere, though our unaided Senses are too gross to perceive either the one or other; since, if the mentioned bristles and ja••ars are in the Glass, and nor in the Animal, they

would appear in like manner in all the small Creatures which in the same light and position are look'd on through the Mi∣croscope: And if the ruggedness of surface were in it, and not in the Moon, the same would be seen upon all other distant ob∣jects, that are view'd through the other Optick Instrument. And if there be deceit in those Glasses, Seamen had need beware how they trust them, since the Flags which appear to be those of their Friends in the Perspective, may be really the Colours of their Enemies.

Upon these accounts, Sir, which afford plain and sensible evidence, I wondered much at the Disputers strange suspicion, which had been scarce pardonable in a vul∣gar head; and I know not what to call it in one, that would be thought a Philosopher: But the wary man gave a reason, which made me as much wonder at his Argument, as his Doubt. And to this attend Ye Phi∣losophers of the ROYAL COLLEDGE, and prepare your selves to answer a Demon∣stration from Experience, against your Glas∣ses; Raise your Expectations for a wonderful, convictive Experiment; Let the Mountains travel, and the Birth will follow. [Take two Spectacles (saith the Experimental

Sage) use them at the same time, and you will not see so well as with one singly.] Therefore your Microscopes and Telescopes are impostors. This man, Sir, is a Logician, and no doubt you perceive so. O how I admire this rare faculty of arguing! How dull are our Wits, to those subtile, Eagle∣ey'd Schoolmen, who see Conclusions so far off, through the more unerring Telescopes of their own piercing Understandings? Did ever old man before make this use of his Spectacles? But to leave wondring, let's endeavour to understand this Philosophy of Chue. How a man may see by Spectacles, that Perspectives are deceitful. [We can see better through one pair, than two] saith the deep Philosopher. Most sagely observ'd! The Argument begins strongly: But in the Name of Aristotle, whence comes the Con∣sequence? Therefore Perspectives are falla∣cious.

One Proposition for Sence, And th' other for Convenience.

This fits his purpose to discredit new Discoveries, 'tis no matter how it follows. This Gentleman, you must know Sir, useth to have his word taken among his admiring

Neighbours, and so is not wont to be put to the trouble of proving: but I was so un∣mannerly as to expect it, chusing rather to see with mine own Eyes, than his infallible Spectacles. We can see better—saith the Disputer. How doth he know that? If Perspectives deceive us, though naked sense witness for them, Why may not his single Spectacles be as deceitful as they? These represent things bigger than they are to the unaided sight; and the Philosophical Glasses do but the same thing, in a higher degree of magnifying the Object. But we allow him the benefit of his single Spectacles, though he will not be so courteous to our Glasses, and confess his Reverend Experiment of the use of two, but are inquisitive about the Consequence. The Reason of which cer∣tainly must be (if any be intended in it) that our Telescopes and Microscopes have a Glass at each end, which the Man of Sapi∣ence thinks answers the two pair of Specta∣cles, and therfore must render the Re∣presentation deceitful. If this Philosopher had spared some of those thoughts to the profitable Doctrine of Opticks, which he hath spent upon Genus and Species, we had never heard of this Objection, which is as much a reason against the credit of all

perspective Glasses whatsoever, as the Phi∣losophical ones he would discredit. And without more Opticks than those of natu∣ral Vnderstanding, he might, if it had pleased him, have known, that we see bet∣ter through the two Glasses in Perspectives, than any single one; because they are so fashioned and ordered, that the visive rays are better gathered and united by them for the advantage of sight: But in the two Spe∣ctacles, the case is contrary. These things I suggested, and some others from the Di∣optricks, in which this Sage Person was pleased then to conceal his knowledge; and how great that was in these matters, will appear by the Learned Problem he pro∣posed at this period of our Discourse, viz. [Why we cannot see with two pair of Spectacles, better than with one singly? For, saith the Man of Axioms, Vis unita fortior?] A pleasant piece of Phi∣losophy this; and I'le shew the Disputer how strongly he infers from his Maxim, by another Question like it. Why cannot he write better with two Pens, than with a sin∣gle one, since Vis unita fortior? When he hath answered this Quaere, he hath resolved his own. I said in the Discourse, That the reason he gave why one would expect

it should be so, is the reason why 'tis not; and this is plain enough to sense, from the confusion of Vision, which shews, that the rays are not united after the way requisite for the aiding the sight (as I just now inti∣mated) and how that should be, I had here shewn, but that I am ashamed to add more in earnest about a grave foolery. And I confess, Sir, I account these personal matters a kind of Digression from the main thing I intended. To return therefore to my Subject.