RT Book, Section A1 Mahmood, Feroze A1 Matyal, Robina A2 Mathew, Joseph P. A2 Swaminathan, Madhav A2 Ayoub, Chakib M. SR Print(0) ID 6915504 T1 Chapter 4. Quantitative Echocardiography T2 Clinical Manual and Review of Transesophageal Echocardiography, 2e YR 2010 FD 2010 PB The McGraw-Hill Companies PP New York, NY SN 978-0-07-163476-2 LK accessanesthesiology.mhmedical.com/content.aspx?aid=6915504 RD 2024/03/28 AB Christian Doppler, in his 1842 paper titled, “On the Coloured Light of the Binary Stars and Some Other Stars of the Heavens,” was the first to note that stars moving towards the earth emitted blue light while stars moving away from earth radiated red light. Thus, he postulated that the observed frequency of a wave depends on the relative speed of the source and the observer. Although Doppler himself never extended the principle to other natural phenomena, the common observation that the pitch of sound is different for a locomotive approaching the listener than one moving away led to a more widespread application of Doppler's initial observation.