The Effect of Stethoscope-Applied Pressure

T HE diaphragm stethoscope is usually credited to R. C. M. Bowles, an engineer of Suffolk County, Massachusetts, who was issued Letters Patent No. 526-802, October 2, 1894. Previous instruments had employed diaphragms but they were carefully recessed to avoid contact with the skin. Bowles concluded from his studies that sound conveyed by such instruments resulted from vibrations transmitted from the edge of the bell to the membrane "similar to beating a drum on the edge of the frame" and that a diaphragm in direct contact with the skin was more efficient. His improved chest piece introduced