If in the same locality, we are enabled to observe two different bodies, both projected, and to measure the vertical and horizontal distances to the point of fall, we can determine *both the angle of emergence* of the wave-path and the *maximum velocity* of the wave. Thus, for example, let both the bodies, be projected by the second semiphase of the wave, and let and a denote the coordinates in and , of the two trajectories; then by Eq. XL. we have

from which we find

(XLIII.) |

(XLIV.) |

and substituting for its value we find

(XLV.) |

In the case, of *the upper portion of a wall, thrown off from the lower which remains standing*, which is a very frequent one, the equations to apply, are the same as for a body, projected and overturned from the summit; the upper portion turning over first, upon one arris, and then being thrown more or less from the base of the wall, in a trajectory. The preceding equations embrace, probably, every case likely to occur to observation.