The stethoscope was invented by the French physician R.T.H. Laënnec. René Théophile Hyacinthe Laënnec is generally considered to be the father of chest medicine.
History of the Stethoscope
The history of the monaural stethoscope and the binaural stethoscope.
One day in 1816, Laennec is invited by urchins to hear to the scratching of a pin transmitted through the length of a wooden beam. He is thereby inspired to fashion a paper tube to listen to the chests of his patients.