At the seventh article, I have sufficiently demonstrated, that all motion is infinitely propagated, as far as space is filled with body. You allege no fault in the demonstration, but object from sense, _that the skipping of a flea is not propagated to the Indies_. If I ask you how you know it, you may wonder perhaps, but answer you cannot. Are you philosophers, or geometricians, or logicians, more than are the simplest of rural people? or are you not rather less, by as much as he that standeth still in ignorance, is nearer to knowledge, than he that runneth from it by erroneous learning? And, lastly, what an absurd objection is it which you make to the eighth article, where I say that _when two bodies of equal magnitude fall upon a third body, that which falls with greater velocity, imprints the greater motion_? You object, _that not so much the magnitude is to be considered as the weight_; as if the weight made no difference in the velocity, when notwithstanding weight is nothing else but motion downward. Tell me, when a weighty body thrown upwards worketh on the body it meeteth with, do you not then think it worketh the more for the greatness, and the less for the weight. ========== OF THE FAULTS THAT OCCUR IN DEMONSTRATION. TO THE SAME EGREGIOUS PROFESSORS OF THE MATHEMATICS IN THE UNIVERSITY OF OXFORD. LESSON IV. Of twenty articles which you say (of nineteen which I say) make the sixteenth chapter, you except but three, and confidently affirm the rest are false. On the contrary, except three or four faults, such as any geometrician may see proceed not from ignorance of the subject, or from want of the art of demonstration, (and such as any man might have mended of himself) but from security; I affirm that they are all true, and truly demonstrated; and that all your objections proceed from mere ignorance of the mathematics. The first fault you find is this, that I express not (art. 1) what _impetus_ it is, which I would have to be multiplied into the time.