The theory was simple. Longi-tude is a matter of time. Theearth rotates through 360° in24 hours. Each hour of timedifference between two places

is equal to fifteen degrees of longitude.To measure longitude you compare yourown local time with the local time at theGreenwich meridian. The time differencebetween the two places, converted to de-grees, gives the longitude west or east ofGreenwich.

Alexander Dallas Bache, the secondSuperintendent of the U.S. Coast Survey,knew that however simple the theory, inpractice the longitude measurement tech-niques used by the Survey were inaccu-rate and inefficient. In 1846, he launchedan experiment that put time signals onMorse’s “lightning wire.” The experimentsparked the development of the “Ameri-can Method,” a system for longitude de-termination that became the prototype formodern electronic position finding anddistance measuring systems.

When Bache took control of the CoastSurvey in 1843, he brought with him a

Longitude by Wire:The American Method

Richard J. Stachurski

“When, in May, 1844 Morse flashed his first telegraphic

messages over the wires between Washington and Baltimore,

with a transmission time of his signals so short as to be

barely perceptible, it is not to be wondered at that this

time-annihilating device was sufficiently suggestive

to the mind of an astronomer to foreshadow a new

method for determining differences of longitude.”

—C.A. Schott, Assistant in the U.S. Coast and Geodetic Survey, 1897

complete set of family political connec-tions and a vision for American science.Born on July 19, 1806, the Superintendentwas a great-grandson of Benjamin Frank-lin. His grandfather, Alexander James Dal-

las, had served as Secretary of the Trea-sury when Congress established the Sur-vey of the Coast. His uncle, George MifflinDallas, was a former U.S. Senator whowould become vice-president about ayear after Bache’s appointment. Hisbrother-in-law, Robert J. Walker, a U.S.Senator from Mississippi, would be ap-pointed secretary of the Treasury in 1845,and become Bache’s boss. His Aunt Matil-da was married to Representative WilliamWilkins who became Secretary of War in1844, in a period when the Coast Surveydepended on officers on loan from thearmy and navy to fill out its workforce.

Bache, unlike a lot of appointees in anage of blatant political patronage, was ac-tually qualified to do his job. He had writ-ten close to fifty scientific papers on top-ics as different as the combustion of phos-phorous and the explosion of steam boil-ers, and established himself as a respect-ed and well-connected member of theAmerican and European science commu-nities. His close colleagues included sci-entists of the caliber of Joseph Henry, amajor contributor to the emerging scienceof electromagnetism, and later the firsthead of the Smithsonian Institute.

In November 1843, when FerdinandHassler, the cantankerous and exacting firstSuperintendent of the Coast Survey was onhis death bed, Bache’s colleagues generat-ed a short, but intense lobbying campaignon his behalf that “became one of thelargest and best-organized efforts yet un-dertaken by the American scientific com-munity.” On December 11, President Tylerappointed Bache as Hassler’s successor.

The new Superintendent acted quicklyand decisively to answer Congressionalcriticism about the slow pace of the Sur-vey’s mapping and charting work, criti-cism that had plagued his predecessor.Hassler had insisted on mapping one re-gion of the coast at a time, and withhold-ing the publication of charts until the tri-

Alexander Dallas Bache in the field. Second Superintendent of the U.S. Coast Survey.

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angulation of a region was completed,and tied into a measured baseline at bothends to verify accuracy. During Hassler’stwelve year term the Survey did not pub-lish a single chart.

Bache understood the political valueof visible activity and near term results.He organized the coast into eight sec-tions, and made certain that survey andsounding parties were evidently active inevery section. His crews kept pace as con-quest and treaty lengthened the coastline.By 1848 they were working in nineteenstates. In 1849 surveyors were on theWest Coast. Bache also reorganized andre-equipped the Coast Survey offices toincrease the production of finished charts.During his first dozen years as Superin-tendent, the Survey published 64 finishedcharts and 258 preliminary charts and hy-drographic sketches which were printedin more than 100,000 sheets.

With the charting business put in or-der, Bache began to use his family po-litical connections, and his own politi-cal skills to pursue his vision for Amer-ican science. He was determined to es-tablish a professional cadre of Ameri-can scientists who would command therespect of the European scientific com-munities. He was convinced that tomeet his goal, there had to be generousgovernment support for American sci-ence. The Coast Survey provided anear-perfect conduit for channelingthat support. All that was required wasa broader view of the agency’s mission,and some political persuasion.

Geodesy as “Big Science”Science, in the nineteenth century,

was nearly synonymous with geography.Scientists, limited to a local, ground levelview of their planet, struggled to discoverits size and shape, and understand thephysical laws that governed its environ-ment. The Coast Survey, with its missionof coastal mapping, was already in thegeography business, albeit with a strictlypractical emphasis. Bache began to ex-pand the agency’s mission to include twoelements of geographical science, geo-desy, the study of the earth’s size andshape, and geophysics, with the focus ontides and currents, terrestrial magnetism,and meteorology.

Geodesy was literally and figuratively“big science” in the eighteenth and nine-teenth centuries. Mathematicians of thecaliber of Gauss and Bessel pursued thework. Governments sent expeditions toremote corners of the globe to measurethe curvature of the earth. The work doneon the Survey of India excited British na-tional pride.

Bache, anxious for recognition ofAmerican efforts in geodesy, promoted aseries of geodetic initiatives. “The mostimportant and long-lasting” of these in-novations, according to NOAA historianAlbert Theberge, “was the development ofa method to determine differences of lon-gitude by the telegraph, that came to beknown as the ‘American Method’ and wasemulated world wide.”

Bache already understood the basicprinciples of the telegraph when he wasappointed Superintendent of the CoastSurvey. In 1837, while a Professor at theUniversity of Pennsylvania, he had madea tour of Europe with Joseph Henry. To-gether, Bache and Henry had visitedBritish researcher Professor CharlesWheatstone who described to them thedesign of a five wire telegraph that startedexperimental operations in that same year.

Another American, Samuel F.B. Morse,had returned from Europe five years ear-lier obsessed with the idea of developinghis own version of the electric telegraph.Morse was an artist, not a scientist. Hisexperiments went slowly. Henry, in a let-ter to a friend, wrote that Morse was “solittle acquainted with the subject of elec-tricity that he could not make his simplemachine operate through the distance ofa few yards.” Help appeared in the per-sons of Leonard Gale, a professor ofchemistry at New York University, and Al-fred Vail, a young acquaintance who hadmechanical skill and investment dollars tooffer. Congress appropriated $30,000, andthe three entrepreneurs constructed a line

extending the forty miles from Washing-ton to Baltimore. The famous first mes-sage “What hath God wrought?” was senton May 24, 1844.

In the autumn of 1845, Bache contact-ed Sears Cook Walker, an astronomer liv-ing in Philadelphia, and asked him to be-gin making arrangements with the tele-graph company for a longitude experi-ment. Walker, born in Massachusetts, agraduate of Harvard, had been a teacher,insurance actuary, and ill-advised invest-or. Although technically an amateur, hewas also the best theoretical astronomerin America. In 1845, he was flat broke,and ready for a career change. With arecommendation from Bache, he madethe transition from amateur astronomer toscientific professional when he joined thestaff of the Naval Observatory in Wash-ington, D.C.

By October 3, 1846, Bache and Walk-er had agreed on the telegraph proce-dure, and issued lithographed instructionsfor the guidance of the experimenters. OnOctober 10, 1846, Walker, with Navy Lieu-

tenants Mathew Maury and John Almy es-tablished a circuit between the U.S. NavalObservatory in Washington, D.C. and theCentral High School Observatory in Phil-adelphia. As pre-selected stars crossedthe meridian at Philadelphia, Professor E.O. Kendall noted the time of their pas-sage and telegraphed it to the Naval Ob-servatory. In Washington, Almy observedthe passage of those same stars across thelocal meridian. As each star passed, henotified Walker who recorded the timeand telegraphed it to Philadelphia. Theexperimenters compared the times ofpassage of each star at each station and

George Mifflin Dallas. Vice-President under President Polk. Uncle of Alexander Dallas Bache.

Chronograph drum without paper used to recordtime ticks during longitude observations

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where a similar local circuit hadbeen wired together.

The chronographic register wasthe critical element in the circuit. Itproduced a record of events thatmade the American Method work.The register’s main componentwas a cylinder that was rotated ata constant speed by a mechanicaldrive. A sheet of recording paperwas secured to the cylinder. Anelectromagnet held a pen againstthe paper so that the pen made acontinuous trace as long as therewas power on the telegraph cir-cuit. Coast Survey “mechanicians”had added a device to the astro-nomical clock that interrupted thelocal circuit when the clock’s pen-dulum reached the bottom of itsarc. The interruption left a distinctmark on the time trace at one sec-ond intervals. When the observer

pressed the finger key at the transit tomark the passage of a star across the site’smeridian, the passage was recorded by amark on the register’s time trace. At theend of their night’s work, the astronomerscould compare the chronograph recordsfor the two stations and compute theirdifference in longitude.

With their equipment in place andwired together, the Coast Survey crewwaited for the late night drop off in com-mercial traffic that would make the maintelegraph circuit available for longitudemeasurements. The Committee of Twen-ty, a group of prominent scientists ap-pointed by the American Association forthe Advancement of Science in 1857 toevaluate the progress of the Coast Survey,described the measurement sequence intheir report: “After suitable observationsfor instrument corrections at each station,which are recorded only at the place ofobservation, the clock at the eastern sta-tion is first put in connection with the cir-cuit, so as to write on the chronographs atboth stations. A number of stars, culmi-nating near the zenith of the two stations,are selected by the observers. As they ap-pear first upon the eastern meridian, theirtransit is recorded by the observer strikingthe finger key upon the chronographicregisters at both stations. After an intervalof time equivalent to the difference of lon-gitude between the two places, which ismeasured by the clock, the same stars ap-pear on the western meridian, and the ob-

calculated a difference in longitude of07m 34.14 seconds. The probable errorwas significant, ±0.50 seconds, but theCoast Survey had launched the AmericanMethod on what would become anaround-the-world journey.

Longitude by WireThe experiment’s success drove rapid

improvements in technology and proce-dures. By 1856, longitude by wire was aregular part of Coast Survey fieldwork.Coast Survey Assistant George Dean, re-porting from Macon, Georgia, describedthe equipment used in the field. “Eachparty is furnished with a forty-six-inchtransit, an astronomical clock, a siderealchronometer, a Morse telegraph register, achronographic register, a Grove’s batteryof forty-five cups, and a self- sustainingbattery, either Mathiot’s, Smee’s, or Dan-iels, which is used in the local circuit.”

The station whose longitude was to bemeasured was usually located within twoto six hundred miles of a station with pre-viously measured longitude, although dis-tances up to a thousand miles wereachieved. The distance depended on thequality of the telegraph circuit between thestations. Entrepreneurs were in a hurry tocapitalize on their investment. Electricalengineering was in its infancy. As a result,circuit performance varied wildly depend-ing on the technical know-how of the sys-

tem designers, the wire and insulationused, and the care taken in construction.

At the longitude station, the field par-ty picked an observing site that had aclear sky view and was located near acommercial telegraph office so that a tem-porary local circuit could be extended tothe site. Wherever possible, the surveyteam also made certain that the site wasin full view of local politicians and busi-nessmen who might influence the Sur-vey’s Congressional appropriation. Bache,after all, understood American politics.

On the site, the observers built a tem-porary observatory, “the cost varyingfrom fifty to one hundred dollars, accord-ing to the locality.” They mounted thetransit and the astronomical clock ongranite or marble piers sunk into theground for stability. The transit instru-ment was a telescope specifically design-ed to observe stars as they crossed themeridian, the imaginary north-south linethat passed through the site and markedits longitude. At the base of the transitthey placed a break circuit telegraph key,called a finger key, within easy reach ofthe telescope observer.

The Coast Survey crew then connect-ed the finger key, the astronomical clock,the chronographic register, and a smallbattery to form a local telegraph circuit.When the longitude measurement se-quence required, they could connect thislocal circuit with the main commercialtelegraph line to the other observing site

Joseph Henry, first Secretary of the SmithsonianInstitution. Political ally and friend of AlexanderDallas Bache.

Charles Schott with Davidson meridian instrument

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Daguerreotype of Samuel F. B. Morse from thestudio of Mathew B. Brady.

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gled to drive the errors in baseline andprimary station latitude and longitudemeasurements as close to zero as theoryand practice would allow.

In the time before the telegraph, CoastSurvey observers used three primarymethods to measure longitude: lunar cul-mination, lunar occultation, and the ex-change of chronometers between sites.All three required the transport of localtime in some form from a location with aknown longitude, usually Greenwich, tothe location where a longitude determi-nation was required.

In the case of lunar culmination, theobserver compared the local time that themoon crossed his own meridian, with thetime, recorded in a set of astronomical ta-bles, that the moon crossed the Green-wich meridian. In the occultation case,the observer compared the local time thatthe moon blocked his view of a star withthe Greenwich Time of the same event.Uncertainty about the precise orbital path

urement of the angles between the inter-visible stations. On the bases furnished bythe sides of the primary triangles, a sec-ondary triangulation is next establishedextending along the coast, and over thesmaller bays and sounds, and determin-ing a large number of points at distancesof a few miles apart. Observations for lat-itude and longitude are made at a num-ber of stations of the primary triangula-tion in each section. The differences oflatitude, longitude between these and oth-er stations are then computed, under thesupposition that the earth is a spheroid ofrevolution . . . .” When the shore-basedsurvey crews had precisely mapped thecoastal topography using this triangula-tion process, hydrographic survey shipsmeasured the angles between their ownposition and the coastal stations to fix theexact location of soundings that collec-tively described the bottom contours ofthe sea immediately off the coast.

Challenging FieldConditions

The Coast Survey’stopographical and hy-drographic crews facedthe daunting prospectof triangulating the At-lantic, Gulf, and Pacificcoasts. With their bays,sounds, islands andrivers, the three coast-lines extended formore than 29,000miles. The crewsworked on freezingmountain tops, in fetidswamps, and in dan-gerous shoal water.The instruments theyused were easier tomove across the coun-tryside, but inherentlyless accurate, than theones used to measurebaselines and the posi-tions of primary astro-nomical stations. Fieldconditions, inevitablyamplified errors. Tokeep the accumulatederrors within toleranceand produce a useablechart, Coast Survey sci-entists constantly strug-

The experiment’s success

drove rapid improvements

in technology and

procedures. By 1856,

longitude by wire was a

regular part of Coast

Survey fieldwork.

Meridian telescope

server at this station records this transitprecisely as the other had done; and thedifference of the two records of time is themeasure of the difference of longitude.”

The Coast Survey’s early adoption ofthe telegraph to measure longitude wasmotivated by a real need for greater accu-racy in position measurement that resonat-ed with Bache’s “made in America” vi-sion. The Survey’s mapping processdrove that need. An anonymous CoastSurvey author, writing in 1851, describedthe mapping operations: “In each sectiona baseline of from five to ten miles inlength is measured with all possible accu-racy. A series of triangles, deriving thelength of their sides from this base, is thenestablished along the coast, by the meas-

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of the moon, and inexact measure of themoon’s semi-diameter compromised theaccuracy of both methods.

Chronometer transport had its ownshare of uncertainties, and a full comple-ment of complex logistics. The self-taughtEnglish inventor John Harrison had de-veloped a chronometer accurate and reli-able enough for navigation that came in-to general use in the first half of the nine-teenth century. But as good as these de-vices became, motion, temperature, andminor differences in their manufacturingand assembly still affected their accuracy.Prior to the laying of the transatlantic tele-graph cable, the Coast Survey made morethan 1,200 chronometer exchanges be-tween the United States and England todetermine the exact longitude of the U.S.East Coast, which remained only approx-imate 300 years after its discovery. The re-sults from these expeditions varied overfour seconds of time or nearly nine-tenthsof a mile at latitude 39ºN, despite carefulpackaging and handling, and extensiveexperimentation and calculation designedto characterize and correct errors.

Replacing the “Imperfect Organ”Of the three longitude methods, lunar

culmination was the most liable to errorwith a theoretical limit of accuracy of±0.55 seconds of time. For lunar occulta-tion, the theoretical error was estimatedto be ±0.10 seconds. Benjamin Pierce, therenowned Harvard mathematician whobecame the third Superintendent of the

Reconnaissance in Coast Ranges of California

Coast Survey, estimated thatchronometer transport was capa-ble of accuracies ten timesgreater than lunar culmination,with a probable error of ±0.05seconds.

The real world of long, coldnights and instruments that hadbeen hauled over miles of ruttedroads produced errors much larg-er than the theoretical values.Charles Schott, Assistant in theCoast and Geodetic Survey, pro-vided an example in the agency’s1897 annual report: “. . . from the earlier results ofmoon culminations the geodeticlongitude of Telegraph Hill at SanFrancisco was taken as 8h 09m

33.29s; a report made by the writer inMarch 1855, gave the resulting longitude8h 09m 34.37s depending on 206 moon-culminations observed at seven different

Nautical chart of New YorkHarbor, 1845.There wereearlier sketchesof harbors, butthis was the firstchart producedwith thedistinctive CoastSurvey style.

places and reduced to the station bymeans of chronometer transportations;but in the spring of 1869 San Franciscoand Cambridge (Massachusetts) were di-rectly connected by wire with a resultingdifference of longitude 3h 25m 7.37swhich when referred to Telegraph Hillmakes its longitude 8h 09m 37.46s, or122°24'21 1/2.95, which exceeds the 1885result by 3.1s nearly, or about 46 1/2 whichin the latitude of San Francisco amountsto almost three-quarters of a mile; thus thecountry was considerably wider than hadbeen known before the advent of the tele-graphic method.” Schott calculated thatthe error in the telegraphic longitudemeasurement for San Francisco was±0.055 seconds of time.

The American Method consistentlyproduced that kind of accuracy by substi-tuting the astronomer’s eye for the as-tronomer’s ear. Walker, who left the Nav-al Observatory and joined the Coast Sur-

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The chronographic

register was the

critical element in the

circuit. It produced a

record of events that

made the American

Method work.

longitude from Greenwich to Vladivostokalong a northern route via Moscow. Ger-man and English experimenters measuredthe hours from Greenwich to Madras onthe Indian subcontinent across a tenuousnetwork of wires that vibrated in the windsof Teheran, Karachi, and Bombay. TheUnited States Navy made its contributionin 1881-82, measuring the longitudes fromVladivostok and Madras to Manila. In1903-04, the United States Coast and Geo-detic Survey closed the final gap, measur-ing the time differences from Manila to SanFrancisco via Guam, Midway, and Hon-olulu. The experiment that had first linkedthe Naval Observatory in Washington, D.C.with the Central High School in Philadel-phia in 1846 had literally come full circle.

The next time you turn on your hand-held GPS and wait that interminable two orthree minutes for it to find satellites andcompute your position anywhere on earthwithin a few meters, you might pass thetime by exercising your sense of wonder athow far the American Method has comesince the first clock signals passed throughthose two iron wires stretching from Wash-ington City to Philadelphia.

RICHARD STACHURSKI has had a lifelong in-terest in the exploration and mapping ofAmerica. His two-part article “The Ameri-can Projection,” appeared in April andMay of 2002.

The chronographic register replaced that“imperfect organ” with an automatic timetrace. The astronomers could read thetime trace scale precisely to tenths of asecond and interpolate by eye to hun-dredths of a second.

Closing the Final GapThe American Method and its enabling

chronograph technology followed the“lightning wire” across the United Statesand around the world. After the initial de-termination of longitude between Wash-ington, D.C. and Philadelphia, a networkof telegraphic longitude stations spreadsteadily outward from two focal points—the nation’s capital, and the CambridgeObservatory at Harvard College. It reach-ed Charleston in 1850, Bangor, Maine in1851, and New Orleans in 1858. By 1869,the continental longitude system had ex-panded westward to Los Angeles, and SanFrancisco. By 1897 there were 45 primarylongitude stations in three tiers thatstretched across the country along thenorthern and southern borders andthrough the Midwest.

The first successful Atlantic telegraphcable, between Heart’s Content, New-foundland and Valentia, Ireland, extendedthe network to the Royal Observatory atGreenwich in 1866. The connectionreached Paris in 1872. East of Paris, Ger-man and Russian observers measured the

vey in 1847, described the shortfall inpre-chronograph astronomy: “Through-out the whole range of practical astrono-my, epochs of time and their relative in-tervals have been hitherto measured byastronomers by listening to the beats of aclock or chronometer, and estimating thefraction of a second between them whenany event had occurred, such as a phaseof an eclipse, an occultation of a star, ora bisection of a star, comet, or planet’scentre or limb, by the wires of a transit in-strument. This use of the ear has been amatter of necessity, not of choice. It is, inevery respect, in the subdivision of timeand space, a very imperfect organ. Whilethe eye readily estimates the proportionalparts of a line with the precision of a

This paper tape recording of the historic message transmitted by Samuel F. B. Morse reads when decoded, “What hath God wrought?” It was sent byhim from the Supreme Court room in the Capitol to his assistant, Alfred Vail, in Baltimore. Morse’s early system produced a paper copy with raiseddots and dashes, which were translated later by an operator. Across the top of this historic achievement Morse has given credit to Annie Ellsworth,the young daughter of a good friend, for suggesting to him what message to send. She obtained it from the Bible, Numbers 23:23.

tenth, the ear seldom distinguishes small-er portions of an interval than a fifth.”

The Library of Congress

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