And don't forget the contribution of the U.S. Navy's Vanguard I satellite (still in orbit and still being optically tracked for geodetic measurements), which revealed the slightly "pear-shaped" nature of the Earth: http://home.swipnet.se/~w-52936/index20.htm and http://www.nord-com.net/accot.schulz/Sats/vang_Early/Early_Vanguard.html
-- Jason ----- Original Message ----- From: James R. Frysinger <[EMAIL PROTECTED]> To: U.S. Metric Association <[EMAIL PROTECTED]> Sent: Sunday, January 05, 2003 7:15 AM Subject: [USMA:24366] Re: The Measure of All Things > Bill Potts wrote: > > > > In October, Ken Alder, the author of The Measure of All Things, gave a > > one-hour talk (including a question and answer period) at a bookstore in > > Winnetka, IL. > .... > > He sees the recognition of the error as the beginning of an awareness of the > > concept of uncertainty and points out that, in any case, the very slight > > "lumpiness" of the Earth gives rise to variations in the length of a > > meridian, depending on which meridian is measured. > .... > > I've read the book and Alder's remarks match his writing. His narrative > takes pains to point out that the main goal of the Delambre-Mechain > survey of the meridian was improved precision. Indeed, it had been > surveyed only a few decades earlier and to a precision that would > astonish the modern reader. (Indeed, that prior survey was argued by > many in the Academy to obviate the need for another, but proponents of > greater precision won the day.) > > The motivations behind this quest included a desire to base important > things (such as measures) on natural phenomena instead of human > artifacts and therefore to strive with utmost diligence for greater > precision in observing those phenomena. The newly developed Borda > repeating circle was the tool that the surveyors expected to help them > accomplish this latter goal. (Some models of this circle were calibrated > in degrees and some in grads.) Yet, the impracticality of having every > user of the meter doing his own survey was what led to the manufacture > of the meter-bar standard. And that bar was then expected to be the > prototype (modeled on and representing the Earth) for all > standardization comparisons. At this time, the need for an artifact as a > standard was never doubted as a practical realization; what was > considered necessary was to divest society of anthropomorphic standards > and models. > > In fact, the quest for greater precision succeeded all too well, for > the tastes of some. It was so precise that the scientists discovered the > Earth to be not a regular ellipsoid of revolution, with a set and > uniform "flatness" (oblation factor), but in fact a lumpy thing in which > the flatness-value changed with latitude along the survey meridian. The > results of other surveys (such as the one in Peru) supported this > inferrence. Therefor it was expected that similar surveys along other > meridian lines might obtain differing results! > > There was an expectation that non-uniforities of mass distribution (as > in mountains and valleys) would influence determinations of "straight > down" by a plumb line.* As Alder pointed out, even Newton knew this and > he had tried to estimate the effects of a nearby mountain on a plumb > line. Plumb lines are important in this survey business because the > latitudes measured along this meridian were determined by celestial > navigation. Since no ocean horizon was available, plumb lines had to be > used to measure zenith distances. Subtracting those from a right angle > gave corrected, observed altitudes of the celestial bodies. But the > discovery that the Earth is in fact a lumpy body (today described by a > geopotential model based on a collection of local geoids) was a > startling discovery. What that means is that, even if one could measure > true sea level at various places over the Earth, one would see a lumpy > ocean due to variations in gravitational attraction forces! This gave > birth to modern theories in planetary geology and the realization that > our view of the Earth must be based on more than a few simple > measurements, such as total mass, volume, and eccentricity. > > The other great development was the development of handling > non-identical repeated measurements. At the time of the survey, the > scientist was expected to "throw out" discrepant results. (Even > maintaining a record of such discrepant results and acknowledging their > ejection was a rather new concept not held by many scientists.) The > results of the Delambre-Mechain survey were seminal in providing the > inspiration for the development of the main statistical error analysis > techniques that we today benefit from. When analyzed using modern error > analysis, Mechain made no errors, though he committed the solecism of > trying to cover up what he thought was a discrepancy. > > Therefore, we have the survey (and thus the founders of the metric > system) to thank for modern geology's model of the Earth and for > demonstrating the usefulness, indeed the necessity, of statistical error > analysis. In addition, the founders gave us a start in basing our > measurements on natural phenomena, though at times realized through > human artifice, as well as a hunger for ever greater precision. This was > perhaps France's greatest gift to the world and to modern science. > > Were the time available in my courses, I would require all my physics > students to read this book. > > Jim > > * It was already recognized that the perpendicular to the horizon was > along a line that did not pass through the center of the Earth. In fact, > this is the basis for the need to know the flatness factor's value; with > this, corrections could be made to determine geological latitude. > > -- > Metric Methods(SM) "Don't be late to metricate!" > James R. Frysinger, LCAMS http://www.metricmethods.com/ > 10 Captiva Row e-mail: [EMAIL PROTECTED] > Charleston, SC 29407 phone: 843.225.6789 >
