SEC, Vlil.l OF NATURAL PHILOSOPHY. »57 directions ; and the obstacle NBCK being perforated in BC, let all the pressure be intercepted but the coniform part A PQ, pass ing through the circular hole BC. Let the cone APQ, be divided into frustums by the transverse plants, de, fg, Id. Then while the cone ABO, propagating the pressure, urges the conic frustum. degf beyond it on the superficies de, and this frustum urges the next frustum fgih on the superficies/g", and that frustum urges a third frustum, and so in infinitum ; it is manifest (by the third Law) that the first frustum defg is, by the re-action of the second frustum fghi, as much urged and pressed on the superficies fg, as it urges and presses that second frustum. Therefore the frustum degf is compressed on both sides, that is, between the cone Ade and the frustum fhig; and therefore (by Case 6, Prop. XtX) cannot preserve its figure, unless it be compressed with the same force on all sides. Therefore with the same force with which it is pressed on the superficies de,fg, it will endeavour to break forth at the sides df, eg ; and there (being not in the least tenacious or hard, but perfectly fluid) it will run out, expanding it self,- unless there be an ambient fluid opposing that endeavour. Therefore, by the effort it makes to run out, it will press the ambient fluid, at its sides df, eg, with the same force that it does the frustum fylti ; and therefore, the pressure will be propagated as much from the sides df, e°~, into the spaces NO, KL this way and that way, as it is propagated from the srptrficies/g- towards PQ,. QJE.D. PROPOSITION XLII. THEOREM XXXIII. All motion propagated through a fluid diverges from a rectilinear pro* gress into ///.« unmoved spaces. CASE 1. Let a motion be propagated from the point A through the hole BC, and, if it be possible, let it proceed in the conic space BCQP according to right lines diverging from the point A. And let us first sup pose this motion to be that of waves in the surface of standing water ; and let de,fg, hi, kl, &c., be the tops of the several waves, divided from each other by as any intermediate valleys or hollows. Then, because the water in tht