4. _Time_ is exposed, not only by the exposition of a line, but also of some moveable thing, which is moved uniformly upon that line, or at least is supposed so to be moved. For, seeing time is an idea of motion, in which we consider former and latter, that is succession, it is not sufficient for the exposition of time that a line be described; but we must also have in our mind an imagination of some moveable thing passing over that line; and the motion of it must be uniform, that time may be divided and compounded as often as there shall be need. And, therefore, when philosophers, in their demonstrations, draw a line, and say, _Let that line be time_, it is to be understood as if they said, _Let the conception of uniform motion upon that line, be time_. For though the circles in dials be lines, yet they are not of themselves sufficient to note time by, except also there be, or be supposed to be, a motion of the shadow or the hand. [Sidenote: How number is exposed.] 5. _Number_ is exposed, either by the exposition of points, or of the names of number, _one_, _two_, _three_, _&c._; and those points must not be contiguous, so as that they cannot be distinguished by notes, but they must be so placed that they may be _discerned_ one from another; for, from this it is, that number is called _discreet quantity_, whereas all quantity, which is designed by motion, is called _continual quantity_. But that number may be exposed by the names of number, it is necessary that they be recited by heart and in order, as one, two, three, &c.; for by saying one, one, one, and so forward, we know not what number we are at beyond two or three; which also appear to us in this manner, not as number, but as figure. [Sidenote: How velocity is exposed.] 6. For the exposition of _velocity_, which, by the definition thereof, is a motion which, in a certain time, passeth over a certain space, it is requisite, not only that time be exposed, but that there be also exposed that space which is transmitted by the body, whose velocity we would determine; and that a body be understood to be moved in that space also; so that there must be exposed two lines, upon one of which uniform motion must be understood to be made, that the time may be determined; and, upon the other, the velocity is to be computed. As if we would expose the velocity of the we would expose the velocity of the body A, we draw two lines A B and C D, and place a body in C also; which done, we say the velocity of the body A is so great, that it passeth over the line A B in the same time in which the body C passeth over the line C D with uniform motion. A B ------ C D ------ [Sidenote: How weight is exposed.] 7. _Weight_ is exposed by any heavy body, of what matter soever, so it be always alike heavy. [Sidenote: How the proportion of magnitudes is exposed.]