Stethoscope

With four toothed wheels each 75 mm dia, fixed 6 mm apart on a shaft, projecting as spindle with slight taper at its end. Wheels have 36, 45, 54, and 72 teeth respectively, used with whirling table

It comprises two aluminium tubes telescoping into each other, so that the column of air within the tubes may be altered from 30 cms to 53 cms, outer tube fits into a wooden base.