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Show Why Billiard Balls Click WHAT makes the "click" when two billiard balls or other, spheres of any solid material ma-terial strike each other? Professor Pro-fessor Banerjl has found that the distribution of the intensity of the sound in various directions around the line of impact is very remarkable, remark-able, and he has found methods of measuring the force of these sounds so exactly that he is able to set down the following conclusions: The sound, he explains, is nut due fas has been hitherto thought) to the vibrations of the spheres,, which in any ordinary material' such as ivory, w-ood or metal are both too high in pitch to be audible, and too faint in intensity to be heard. The "click" is due to air vibrations vi-brations caused by the reversal of the motion of ths spheres as a whole. He has ascertained that the intensity in-tensity is at its h'.2hest, or maximum, maxi-mum, in a line joining the centres of the spheres, li gradually diminishes di-minishes almost to zero at an angle of about 67 degrees with a line joining the centres, when it again increases to a second maximum at an angle of 90 degrees. In other words the "click" is loudest at the very point of contact of the spheres which is what we would naturally expect. But the surprising discovery is that this loud "click" is also heard at a perfect right-angle to the point of contact of thej spheres, which would tend to show that the radiations radi-ations of sound are caught by the high points of the spheres, and then given off, for the angle of 90 degrees marks the high point on the way around the spheres from the point of contact. ) This may be set down as an important im-portant discovery in the field of acoustics, one which will necessi- j tate the rewriting of many paragraphs para-graphs in the ordinary elementary works on physics. These have hitherto always suggested that the sound of the "click" Is due to the vibration of the material in tha spheres. |