We may represent the two tendencies to movement produced by the force _P_, by drawing additional dotted lines, one horizontally to the left (_R_) and the other vertically (_L_); and it is known that if we let the length of the line _P_ represent to some convenient scale the amount of direct pressure, then the lengths of _R_ and _L_ will also represent to the same scale the amounts of horizontal and vertical force due to the pressure. If the weight of kite and tail exceeds the vertical force _L_, the kite will descend: if these weights are less than that force, the kite will ascend. If they are precisely equal to it, the kite will neither ascend nor descend. The ratio of _L_ to _R_ is determined by the slope of _P_; and this is fixed by the slope of _ab_; so that we have the most important conclusion: _not only does the amount of direct pressure (P) depend upon the obliquity of the surface with the breeze (as has already been shown), but the relation of vertical force (which sustains the kite) to horizontal force also depends on the same obliquity_. For example, if the kite were flying almost directly above the boy who held the string, so that _ab_ became almost horizontal, _P_ would be nearly vertical and _L_ would be much greater than _R_. On the other hand, if _ab_ were nearly vertical, the kite flying at low elevation, the string and the direct pressure would be nearly horizontal and _L_ would be much less than _R_. The force _L_ which lifts the kite seems to increase while _R_ decreases, as the kite ascends: but _L_ may not actually increase, because it depends upon the amount of direct pressure, _P_, as well as upon the direction of this pressure; and the amount of direct pressure steadily decreases during ascent, on account of the increasing obliquity of _ab_ with _V_. All of this is of course dependent on the assumption that the kite always has the same inclination to the string, and the described resolution of the forces, although answering for illustrative purposes, is technically incorrect. It seems to be the wind velocity, then, which holds up the kite: but in reality the string is just as necessary as the wind. If there is no string, and the wind blows the kite with it, the kite comes down, because the pressure is wholly due to a relative velocity as between kite and wind. The wind exerts a pressure against the rear of a railway train, if it happens to be blowing in that direction, and if we stood on the rear platform of a stationary train we should feel that pressure: but if the train is started up and caused to move at the same speed as the wind there would be no pressure whatever.