The _caduceus_ rocket has not much more than half the power of ascension as the single rockets; because, being composed of two rockets placed at an angle of 90 degrees, with the usual counterpoise, (the stick), it forms in its flight a serpentine motion resembling two spiral lines, or double worm; and although by reason of the stick it ascends vertically, yet the great resistance it meets with from the air, in consequence of this motion, causes its flight to be considerably retarded. On the contrary, when rockets are fixed one on the top of another, called _towering rockets_, their effect is not at all diminished; for they experience no additional resistance, as the small rocket is placed in the head of the large one; and when the latter arrives at the maximum of elevation, it communicates fire to the former, which then rises as far beyond the first, if not higher, in consequence of the pressure of the atmosphere being less, as it would, if discharged by itself on the ground. Sky rockets, however, which are merely placed on one stick, do not, unless so required, act in this manner. Although two, three, or more, may be so arranged, yet the intention is nothing more than to combine their effect, so that their tails may appear as one stream of fire. Nevertheless, they may be so arranged, as that when one is consumed, another may take its place, and produce a new volume of fire, and, in this case, they would mount to a great height. _Tourbillons_, usually called the common or table _tourbillons_, which receive their name from the whirling motion they take in their flight, produce also, by the arrangement of their cases, and the cross stick which serves as a balance, a horizontal and rotary motion; and while one part of the fire serves to elevate them, another part, issuing in a horizontal direction, but at opposite sides and extremities, gives to the tourbillon a wheeling motion. The mosaic tourbillons are of a different kind, and intended for another effect. Tourbillons of this kind preserve a regular and constant motion.