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Christian Doppler, professor of mathematics at Prague, enounced in 1842 the theorm that the colour of a luminous body, like the pitch of a sonorous body, must be changed by movements of approach or recession. The reason is this.
If the marksman advances, say twenty paces between each discharge of his rifle, it is evident that the shots will fall faster on the target than if he stood still; if, on the contrary, he retires by the same amount, they will strike at correspondingly longer intervals. The result will of course be the same whether the target or the marksman be in movement. So far Doppler was altogether right.
Belopolski's observation, it may be remarked, was based upon what is known as the Doppler principle, which is employed in measuring the motion of stars in the line of sight, and in other cases of rapidly moving sources of light.
For a complete knowledge of a star's motion the proper motion and parallax must also be known. When Huggins first applied the Doppler principle to measure velocities in the line of sight, the faintness of star spectra diminished the accuracy; but Vogel, in 1888, overcame this to a great extent by long exposures of photographic plates.
In 1982 Costas had been trying for three years, without success, to hear his own signal via Moonbounce. The reason for his failure was that he was unaware of a very basic fact. "I was completely ignorant of the Doppler shift effect," Costas told me. "The frequency of received signals varies according to the position of the moon.
It has also invaded optics; and by relying on the principle of Doppler, Professor Michelson has succeeded in obtaining from it an explanation of the length presented by the spectral rays of even the most rarefied gases.
His voice was shaking just a bit when he called into the speaker: "Battle stations, everyone!" Gunnar took off for the needle-nosed instrument which he had grown to hate. Odin stood by to help with the screens. "Watch forward now!" Ato warned. "Sight at thirty degrees above the equator of The Nebula. Adjust for Doppler X over Y. We have him on the screens now.
H. A. Rowland developed the art of constructing these gratings, which requires great technical skill, and for this astronomers owe him a debt of gratitude. In 1842 Doppler proved that the colour of a luminous body, like the pitch or note of a sounding body, must be changed by velocity of approach or recession.
Angle, strength and Doppler movement were computed to find course and distance. A few minutes of flight were enough to get within range of the far weaker transmitter in the drop-capsule. Homing on this signal was so simple, a human pilot could have done it himself. The shining sphere loomed up, then vanished out of sight of the viewports as the ship rotated to bring the spacelock into line.
Sherwood was born at Lyons, New York, of good American stock. His father was his teacher until the age of seventeen, when he studied with Heimberger, Pychowski, and Dr. William Mason. He studied in Europe with Kullak and Deppe, Scotson Clark, Weitzmann, Doppler, Wuerst, and Richter. He was for a time organist in Stuttgart and later in Berlin.
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