We may remark also, from the premises already established, that the first motion of the rocket, like all other motions not produced by a great momentary impulse, is slow; and before the stick is clear of the flame, gravity has been acting upon the rocket, and depressed it below its natural position, while the stick is prevented from being equally depressed, by the top of the frame; so that the angle of projection is in fact considerably less than the angle of the frame, or slope of the rocket's first position. In consequence of this, the rocket has the appearance of falling the moment after projection; and, for this reason also, the angle for producing the greatest range of a rocket exceeds very considerably that which gives the extreme range of a shell projected from a mortar. There are various propositions given by Mr. Moore respecting rockets, but to give the calculus, &c. would take up more room than we could appropriate to this abstract question. The nature of these propositions, however, may be given in a few words, _viz_: The strength or force of the gas from the inflamed composition of a rocket being given, as also the weight and quantity of the composition, the time of its burning, and the weight and dimensions of the case and stick, to find the height to which it will ascend, when projected perpendicularly upwards. After making the necessary calculation, he concludes by observing, that, having determined the height of the rocket, and its velocity, when the composition is just consumed, it follows that its whole height may be determined in the usual manner by the known formula, for the ascent and descent of heavy bodies. Another proposition is that of determining the path of a rocket near the earth's surface, neglecting the resistance of the air; and among others, for finding the horizontal range of a rocket, the angle of elevation, and the time the composition is on fire, being given. The observations of Mr. Peyre, (_Le Mouvement Igné_,) are confined principally to the effects of gunpowder; and although applied to the use of gunpowder, and the theory of its explosive effects, yet there is nothing in immediate relation with this subject. The generation of gaseous fluid, and its impelling power, and the consequent recoil of pieces, predicated in fact on the ingenious experiments and conclusions of Mr. Robins, may furnish some data on this head. But the principles of accelerated motion, on which the effective power of war-rockets depends, this accelerated motion being no other than the acquired velocity of their recoil, necessarily involves a question of a different kind from that of common projectiles.