Kundt'S Apparatus Compare the ratio of the velocity of sound in brass to that in air. With our device, this elegant nineteenth century experiment is easy to perform today. Rub a brass tube (36 x 8 x 5") until it vibrates and watch the powder inside accumulate at nodal points. Measure the spacing between nodal points and compare with the length of the brass rod. Includes instructions. You need lycopodium or other fine powder. Qty :