The Pulfrich Effect: Carters (2009) on Simon Newcomb

Carter, William E. and Carter, Merri Sue. Simon Newcomb, America's first great astronomer. Physics Today, 2009, 62(2), 46 - 51.

Copyright (c) 2009, American Institute of Physics. Quoted here under fair use.

The full text of this work is available free online at The American Institute of Physics.

Gray 1921, p. 416:  Astatic galvanometer with directing magnet. Simon Newcomb, America's first great astronomer, by William E. and Merri Sue Carter.


This paper sketches the biography of Simon Newcomb, an early American astronomer whose interests were wide-ranging and whose influence changed the course of astronomy in numerous ways.

Newcomb's work on the speed of light is described as inspirational to Albert Michelson, of Michelson and Morley fame.

A few passages describe the problems which were in part solved in France by the concept of personal equation of astronomers:

Newcomb's Problem:

p. 48: "As busy as his day-to-day duties kept him, Newcomb still found time to think about the rapidly approaching 1874 transit of Venus. . . .
"The traditional method of observing a transit was to record the precise times that the edges of the planet and the Sun appeared to come into contact -- twice as the planet moved onto the face of the Sun and twice as it moved off of it.
The relative motion between Venus and the Sun, as seen from Earth, is slow. Typically, it takes about 20 minutes between the first and second contacts and 20 minutes between the third and fourth contacts, which happen several hours later. Newcomb knew that different observers at the same location often disagreed on the exact time of each contact. . . .
Estimates of the astronomical unit [jmw: the diameter of the Earth's orbit] derived by different researchers using observations of the 1769 transit varied by as much as 5% -- roughly 7.5 million kilometers.
"One problem in observing transits by eye was that there was no way for observers to practice [jmw: cf. Charles Wolf's training methods]. Four planet-Sun contacts that occur once, or at most twice, in a lifetime hardly provide opportunities to develop skill.
But there was an even more fundamental problem: The Sun has no fixed, sharply defined edge. Each observer had to draw an edge in his own mind's eye. Newcomb concluded that the only hope of collecting observations of the upcoming transits that would yield an estimate of the astronomical unit to better than about 1%, about 1.5 million kilometers, was to use the emerging technology of photography. . . ."

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The Pulfrich Effect, SIU-C. Last updated 2009-06-06