Yours sincerely
Editor

Nature has endowed us with numerous mysteries that, when unravelled, would benefit mankind and society as a whole.  Power of observation, coupled with imagination and scientific temperament, leads to a deeper understanding of the secrets that Nature has to offer.  A spark of an idea inspired by nature  can lead to a discovery that benefits the whole world.  One such revelation came to Johann Christian Andreas Doppler who cherished observations of natural phenomena.

In his own words, "We know from general experience that a ship of moderately deep draught which is steering toward the oncoming waves has to receive, in the same period of time, more waves and with a greater impact than one which is not moving or is even moving along in the direction. If this is valid for the waves of water, then why should it not also be applied with necessary modification to air and ether waves?"

Stated in simple terms, when standing adjacent to a railway track, an observer notices a change in pitch or frequency of sound coming from a train whistle as the train approaches or moves away.

A change in the observed frequency of a wave, as of sound or light, occurring when the source and observer are in motion relative to each other, with the frequency increasing when the source and observer approach each other and decreasing when they move apart. The motion of the source causes a real shift in frequency of the wave, while the motion of the observer produces only an apparent shift in frequency. Also called Doppler shift

Study of the Doppler effect has benefitted Astronomy in understanding the Expansion of Universe in addition to estimating the temperature of Gaseous masses in the Universe.

Law enforcement agencies use Radars based on this principle to estimate travelling velocities of speeding motorists.

Laser Doppler Velocimeter and Acoustic Doppler Velocimeter are used to measure flow velocities in a non-intrusive manner.  Doppler shift of a target is used to ascertain the speed of a submarine in military applications.

Greatest benefit to humankind has been the velocity measurements associated with blood flow for monitoring valve function and areas.  Calculation of cardiac output, mitral valve regurgitation among others are regularly studied using this principle.  Doppler principle finds extensive use in Medical Ultrasonography of Neural and Obstetric diagnostics, immensely benefitting mankind .

While acknowledging the limitations of his calculations, Doppler had, in his publication referring to this phenomenon, admitted with remarkable foresight, "It is almost to be accepted with certainty that this will in the not too distant future offer astronomers a welcome means to determine the movements and distances of such stars which, because of their unmeasurable distances from us and the consequent smallness of the parallactic angles, until this moment hardly presented the hope of such measurements and determinations."

Discovery of this phenomenon had proved very important during the proposition of the Theory of Relativity by Albert Einstein later.  Little is known that one of the students interviewed by him for admission to the Royal Imperial University, Vienna, was Gregor Mendel who went on to become the father of modern genetics.

(Images Source: Kettering University)