It is evident, that by this mode, an incessant and tremendous fire may be maintained, which it would be next to impossible for an advancing enemy to pass through, not only from its quantity and the weight and destructive nature of the ammunition, but from the closeness of its lines and its contiguity to the ground; leaving, in fact, no space in front which must not be passed over and ploughed up after very few rounds. As both these operations are supposed to be employed in defensive warfare, and therefore in fixed stations, there is no difficulty involved in the establishment of a sufficient depôt of ammunition for carrying them on upon the most extensive scale; though it is obviously impossible to accomplish any thing approaching this system of defence, by the ordinary means of artillery. [Illustration: _Plate 8_  Fig. 1  Fig. 2] THE USE OF ROCKETS IN THE ATTACK AND DEFENCE OF FORTIFIED PLACES. Plate 9, Fig. 1, represents the advanced batteries and approaches in the attack of some fortress, where an imperfect breach being supposed to have been made in the salient angle of any bastion, large Rockets, weighing each from two to three hundred weight or more, and being each loaded with not less than a barrel of powder, are fired into the ruins after the revetment is broken, in order, by continual explosions, to render the breach practicable in the most expeditious way. To insure every Rocket that is fired having the desired effect, they are so heavily laden, as not to rise off the ground when fired along it; and under these circumstances are placed in a small shallow trench, run along to the foot of the glacis, from the nearest point of the third parallel, and in a direct line for the breach: by this means, the Rockets being laid in this trench will invariably pursue exactly the same course, and every one of them will be infallibly lodged in the breach. It is evident, that the whole of this is intended as a night operation, and a few hours would suffice, not only for running forward the trench, which need not be more than 18 inches deep, and about nine inches wide, undiscovered, but also for firing a sufficient number of Rockets to make a most complete breach before the enemy could take means to prevent the combinations of the operation. From the experiments I have lately made, I have reason to believe, that Rockets much larger than those above mentioned may be formed for this description of service--Rockets from half a ton to a ton weight; which being driven in very strong and massive cast iron cases, may possess such strength and force, that, being fired by a process similar to that above described, even against the revetment of any fortress, unimpaired by a cannonade, it shall, by its mass and form, pierce the same; and having pierced it, shall, with one explosion of several barrels of powder, blow such portion of the masonry into the ditch, as shall, with very few rounds, complete a practicable breach.