Seventhly, it may be considered from the diversity of the _medium_; as one motion may be made in _vacuity_ or _empty place_; another in a _fluid_; another in a _consistent medium_, that is, a _medium_ whose parts are by some power so _consistent_ and _cohering_, that no part of the same will yield to the movent, unless the whole yield also. Eighthly, when a moved body is considered as having parts, there arises another distinction of motion into _simple_ and _compound_. _Simple_, when all the several parts describe several equal lines; _compounded_, when the lines described are unequal. [Sidenote: The way by which the first endeavour of bodies moved tendeth.] 5. All endeavour tends towards that part, that is to say, in that way which is determined by the motion of the movent, if the movent be but one; or, if there be many movents, in that way which their concourse determines. For example, if a moved body have direct motion, its first endeavour will be in a strait line; if it have circular motion, its first endeavour will be in the circumference of a circle. [Sidenote: In motion, which it made by concourse, one of the movents ceasing, the endeavour is made by the way by which the rest tend.] 6. And whatsoever the line be, in which a body has its motion from the concourse of two movents, as soon as in any point thereof the force of one of the movents ceases, there immediately the former endeavour of that body will be changed into an endeavour in the line of the other movent. Wherefore, when any body is carried on by the concourse of two winds, one of those winds ceasing, the endeavour and motion of that body will be in that line, in which it would have been carried by that wind alone which blows still. And in the describing of a circle, where that which is moved has its motion determined by a movent in a tangent, and by the radius which keeps it in a certain distance from the centre, if the retention of the radius cease, that endeavour, which was in the circumference of the circle, will now be in the tangent, that is, in a strait line. For, seeing endeavour is computed in a less part of the circumference than can be given, that is, in a point, the way by which a body is moved in the circumference is compounded of innumerable strait lines, of which every one is less than can be given; which are therefore called points. Wherefore when any body, which is moved in the circumference of a circle, is freed from the retention of the radius, it will proceed in one of those strait lines, that is, in a tangent. [Sidenote: All endeavour is propagated in infinitum.]