towards the Jesuits. But you taking no notice of the word _special_, would have men think I held, that human sciences might be acquired without any help of God. And thereupon proceed in a great deal of ill language to the end of your objections to this chapter. But I shall take notice of your manners for altogether in my next lesson. At the nineteenth chapter you see not, you say, the method. Like enough. In this chapter I consider not the cause of reflection, which consisteth in the resistance of bodies natural; but I consider the consequences, arising from the supposition of the equality of the angle of reflection, to that of incidence; leaving the causes both of reflection, and of refraction, to be handled together in the twenty-fourth chapter. Which method, think what you will, I still think best. Secondly, you say I define not, here, but many chapters after, what an angle of incidence, and what an angle of reflection is. Had you not been more hasty than diligent readers, you had found that those definitions of the angle of incidence, and of reflection, were here set down in the first article, and not deferred to the twenty-fourth. Let not therefore your own oversight be any more brought in for an objection. Thirdly, you say there is no great difficulty in the business of this chapter. It may be so, now it is down; but before it was done, I doubt not but you that are a professor would have done the same, as well as you have done that of the _Angle of Contact_ , or the business of your _Arithmetica Infinitorum_ . But what a novice in geometry would have done I cannot tell. To the third, fourth, and fifth article, you object a want of determination; and show it by instance, as to the third article. But what those determinations should be, you determine not, because you could not. The words in the third article, are first these, _if there fall two straight lines parallel, &c._ which is too general. It should be, _if there fall the same way two straight lines parallel, &c._ Next these, _their reflected lines produced inwards shall make an angle, &c._ This also is too general. I should have said, _their reflected lines produced inwards, if they meet within, shall make an angle, &c._ Which done, both this article and the fourth and fifth are fully demonstrated. And without it, an intelligent reader had been satisfied, supplying the want himself by the construction.