Due correction for Mr Hobbes· Or Schoole discipline, for not saying his lessons right. In answer to his Six lessons, directed to the professors of mathematicks. / By the professor of geometry.

SECT. VI. My Treatise of Conick Sections vindicated. (Book 6)

AS for my Treatise of Conick Sections, you say, it is so co∣vered over with the Scab of Symbols, that you had not the patience to examine whether it be well or ill demon∣strated. A very fine way of confutation; and with much case. You have not the patience to examine it, (that is, in plain Eng∣lish, you do not understand it,) Ergo I have performed nothing in any of my Books (for that is the inference in the same page, p. 49.) 〈 in non-Latin alphabet 〉〈 in non-Latin alphabet 〉. But, Sir, must I be bound to tell you a tale, and find you ears too? Is it not lawfull for me to write Symbols, till you can understand them? Sir, they were not written for you to read, but for them that can.

However, whether you understand it or not, yet some∣what you observe, you say, (though you have not the patience to examine whether it be well or ill.) Pray lets heare your Observations; (for they be like to be wise ones.)

You observe, you say, that I find a Tangent to a point given in a Section, by a Diameter given: (very good; There's no hurt in that, I hope, is there?) and in the next Chapter, I teach the finding of a Diameter. You should have done well to have told us, where to find those Chapters. For I do not remember, that that Treatise is at all divided into Chapters. Well! but suppose I had in one Chapter, by the help of Diam••ter given, found a Tangent; in another Chapter, by the help of a Tangent, found a Diameter: Had there been any hurt in all this?

You observe also, you say, that I call the Parameter an Ima∣ginary line, as if the place thereof were lesse determined then the Diameter it selfe. (But did you observe, whether I did well or ill, so to call it?) And then, you say, I take a mean pro∣poirtionall between the intercepted Diameter, and its contiguous ordinate line, to find it. Pray tell me where you observed that. For, had I observed it, I should have observed it as a great fault; and not said as you doe, And 'tis true, I find it. For, believe mee, that is not the way to find a Parameter. Nor

doe I give you any such direction. You may (in a Parabo∣la) find the Parameter by taking a third Proportionall, but not by taking a Mean Proportionall, to those two lines. You say, The Parameter hath a determined quantity. Yes doubt∣lesse. And, in some Writers, it hath a determined Positi∣on too (viz. in the Tangent of the vertex:) But because I make no use of any such position, I give you leave either to draw it where you will, or not to draw it at all. For by a Parameter, I mean only, a line of such a length, where e∣ver it be; whether at Rome, or Naples, or in M. Hobs his brain. They that make use of the Parameters position, as inferring any thing from it, must assigne it a certain place. I make use only of its bignesse, and therefore care not where it stand.

Lastly you observe, you say, that I doe not shew how to find the Focus. (nor was) bound to doe.) And that's all.

And is not this a worthy confutation? Yes doubtlesse; worthy of you; For how could you else inferre, That I have performed nothing in any of my Books; if you had not confuted them all.

And thus much of those three Treatises. Which, you see are come off safe and sound, without the losse of leg or limb. And with this advantage, (if M. Hobs his testimo∣ny, in point of skill, were worth any thing,) that they have obtained from him as ample a Testimony as he is able to give. viz. That when as he hath imployed the utmost both of his skill and malice, to find what faults he could, he hath not been able to discover any one: (which Testi∣mony, from a considerable adversary, would have been worth something; but, from M. Hobs, J confesse, it signifies little:) and all the attempts he hath made to that purpose, have not been so strong, but that a Butter-fly might have broken through them.