National Geographic : 1896 Jul
THE ABERRA TION OF SOUND able that for some distance from the source the motion is of a projectile character."* The breaking of the transoms over doors, while the window was uninjured, and the breaking of the windows unexposed to the direct force of the explosion are very interesting phenomena, and I wish to offer an explanation which I think will account for the facts observed. The path of the maximum of disturb ance results largely from the unequal resistance of the air, and while at the actual center of explosion the pressure may be in " concentric shells," at a very short distance it becomes stellar. The changing pressure of the wind, as shown by Professor Lang ley's experiments, and the shape of the flame in an explosion (stellar) lead one to this conclusion. As the maximum wave moves from the focus, the air forming it is constantly changing, and the following sketch illustrates the path of an air particle as I believe it to be: 0 A, B, and C are air particles in the path of a maximum wave traveling along the line 0 P. The motion of each is first along the line of 0 P, away from the focus, a result of direct impact of other particles, then back to its original position, or near it, the track forming a closed curve. When the particle is in the posi tion A', B', or C', its motion is toward the focus of the explosion, and so any damage it might do would be evidenced by a break ing of objects unexposed to the force of the direct wave. In the case of the transoms mentioned above, the back thrust which broke the glass and frame was cushioned by the air in the room, and so the window was not injured. * Encyclopedia Britannica,ninth edition, vol. xxiv, p. 418.