Science and Seventeenth Century Navigation DWAYNE R

SOCIAL SCIENCES

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Science and Seventeenth Century Navigation DWAYNE R. MASON, Norman

Until the advent of electronic navigational devices there had been only two important techniques for determining a ship's position when out of sight of land: dead-reckoning and celestial navigation. Dead-reckon ing consisted of cumulative plots ot d.t8tancee and dJrection ot travel on a plane chart. The navigator plotted each segment, beg1nn1ng at the end ot the previous segment and, it his information concerning the ship's progreu were correct and. If he had plotted carefully, he was able to make an accurate estimate ot his position at any time. Information conceming the ship's progress was supplied, in part, by the shlp's compau but, for the most part, the navigator had to rely upon his own skill in estimating speed, leeway, and the effect of currents.' The theoretical framework upon which celestial navigation was founded was at leut as old as Ptolemy. Almageat. In parts three and four of Book I, Ptolemy hypothesizes the spherical movement of the heavens and the sphericity ot the earth. As arguments for these hypotheses, Ptolemy asserted that the ditfereJ1Ce. in the recorded times ot ob8ervattona of celestial phenomena was detenninecS by the differences in the longitudes ot the places of observation. The dlt ferences in the observed altltudN of known stara were due to the dlfter eDCe8 in the latitudes of the placea of Observation.' By taking the eleva- 148 PROC. OF THE OKLA. ACAD. OF SCI. FOR 1963

uon. at zenith, of a known .tar and comparing that value with the one Jlven In an ephemerlde8, prepared tor a place of known latitude, the navlptor could compute the latitude of h1I position. To compute the Ion&1tude by obHrviDg such a rare phenomenon .. a lunar eclipse, required an accurate determination of local sun time. Such an able dead-reckoning navigator u Chriatopher ColumbU8 (1451-1506) made only infrequent celea tJa1 obMrvatioD8 to utlmate h1I latitude. These estlmatea later proved to be .. much sa twenty degrees in error.' Seventeenth century captains relled very heavUy upon dead-reckoning Davtption and t}le accuracy resulting varied with the skJll of the navigator. To Ihlpownen, such methods seemed haphazard. Serious errors could be extremely expeD8ive. Governments and private individuala commiBsloned ICholan to either improve emtlng methods ot navigation or to invent new on..• Thomu Hariot (1560-1621), sponsored by Sir Walter Raleigh, found that thoM captains who did use celestial observations to ascertain their latitude, were frequently using tables of decUnatlon as much as one bundred years out of date. Harlot prepared new tables, making very minor corrections, tor Raleigh's private use. Although Harlot's tables were complied In 1608, English tables tor general use did not appear until leU. A Cambridge Kholar, Edward Wright (1560-1815), In the pay of Lord Cumberland, 80ught to improve dead-reckoning by adapting the Mercator Map into the True Chart. After solving a complicated trigono metric problem, the navigator could plot h1a poaltion on the new Wright Mercator Map.' Maurice of Oranre comml88loned Simon Stevin (1548-1620) to improve Dutch naVigation. Stevln applied the magnetic variation theories of Wil Ham Gilbert (1544-1603) and produced a theory by which, given a ship'. latitude and the local variation of the magnetic compass from true north. the longitude could be computed. Unfortunately, while a good ship'. com .... wu only accurate to one-half point or five and three-quarters degrees, &.clOnic line. of one degree variation were frequently over one hundred mn. apart.' a.meo GaWel (15M-1642) 8Uggested that the occultations of the satel· litea of Jupiter might be useful In finding longitude.' This scheme required not only an accurate value for local 8un time but alao an astronomical te1MCOpe. Chrtat1an HUYleJUI (1629-1695) attempted to his recently per fected pendulum clock to the solution ot the longitude problem.' To find the meridian ODe needed only: an accurate chronometer, a line drawn on the tloor of the Ihlp, and that the ahlp be absolutely motionless whUe the oblervation wu be1ng made. It would seem, at first glance that the problem WU ooe of communication. The navigaton were not sufficiently educated In mathematiCll, the language of astronomy, to comprehend or .ppredate the eoluUons offered them by the ecientlata. The sclenUata, on the other band, eeem to have had ln8uttlclent lnformaUon concerning the problema they were Uked to 8Olveo

To improve the poalblUty of communication, Charles U of England ID8t1tuted a ecbool of mathematic. at CIuist'. Hospital Samuel Pep,. (tal-lTOS), secretary of the Admlralty In 1m, inaugurated an examlM_ UoIl tor DaYal lieutenants which included a section on mathematica.' Wil liam m eomm1a1ODed aD astronomer, Edmund Halley (1856-17U). to ctl'C2WDD&....t. the globe lD BMB ParoMOllr PMIc.."

Goftl'DmeDts Dot only tried to Improve commUDIcatlcma between 8Clen u.ta and DaYlptora but aI80 added the Incentlv. of ftnaDclal rewards. In 1_ PbUlp m of Spala offered 1.000 Crowns to the man who 80lvecl tile SOCIAL SCIENCES H9

problem ot determining longitude at sea. The Estates General of the Neth erlands made an offer of 10,000 Florins at about the same time. Although these rewards rose to 10,000 Crowns and 100,000 Florins respectively, they went uncollected In 1713, the Engllah Parliament not only offered a reward but also financial assistance to anyone who presented a promlalng method for finding the longitude.II

In 1763. John Harrison (1693-1776), an English watchmaker, produced a chronometer sufficiently accurate for use In ascertaining the time dif ference in a star's position relative to the observer and the predicted poet Uon relative to an observatory of known longitude.It The cost of such an instrument was so high that even the Royal Navy could not make a general issue of the navigational chronometer unW 1825.11 The practical solution to the problem of finding one's positlon at lea wu not the result of the creation ot a new astronomical concept or the genius ot a dlIlgent navigator or even the efforts of a fine watchmaker. The practlcabUlty of modem celestial navigation depends upon relatlvely cheap, relatively ac curate instruments, charts. and star tables, coupled wlth sufficient training on the part of the naVigator. With this equipment he 18 able to make the observations and computations by which he may check his dead-reckoning. Modern navigation tables are constructed assuming a stationary spherical earth in the midst of a rotating sphere of fixed stars.

NOTES

'Samuel Eliot Morison, Admiral 0/ the Ocean Sea (Boston: Little Brown and Company, 1952), pp 175-185. 2Claude Ptolemy, "The Almagest:' Great Boo," Of the Wutem World, edt Robert Maynard Hutchens et al. (48 vola; Chicago: Encyclopaedia Britannica Inc., 1952),XVI, pp 7-9. 'Morison, Admiral, p 258. 4Maurlce Ashley, England in the Seventeenth Century (London: Pen guin Books, 1952), P 102. 'E. G. R. Taylor, The Haven/inding Art (New York: Abelard-Schu man, 1957), pp 215-228. 'Ernst Crone, et al. eds., The Principal Worka oj Simon Bteum (8 vola; Amsterdam: C. V. Swets and ZelUnger, 1961), I, pp 411..15. 'Galileo Galllei, "Proposte per la determlnazlone della longituc!lne," Le opera di Galileo GalUei edizione nazionale Botto gU auapicU BUG Maguta U Be IYItalia (20 vola; Flrenze: G. Barbera, 1890-1909). V. pp 418~5. 'Christian Huygena, "InstrucUons concerning the uae ot the pendulum watches for finding the longitude at sea," Ph.~opAicGI TrClMCJCtiont: Gtvi'\9 Some Accompt 0/ the Pruent Undertaking., Btudiea cmd LClbora 01 the rragenWu8 in Many C~le Pa.rt. 0/ the World (London: John Martyn. 1669), IV, #47, pp 937-953. 'R. H. Curtiss, "An Account of the Rise of NavtgatloD," Ann1Ull Bqorl 0/ the Board 01 BegentB 01 the BmUhaonfcln IMtitvte-191' (Wublnlton: Government Printing OUlce, 1920), P 26. -Eugene F. MacPlke ed, Corr~arad PtJfJtJf'8 01 Bclmuf14 BIJl. ley (London: Taylor and Francl8, 1937), p. 226.

"Abott Payson Usher, A Hf8tM"71 0/ Mec1uJfHctJllmHmtfofl8 (Cambridl'e: Harvard University Press, 1961), P 324. 1M PROC. OF THE OKLA. ACAD. OF SCI. FOR 1963 UCbarlea Stnger ~ 01. ed8., A II.tory 01 'l'ec1ntoZogll (4 vola; OXford; CJarendon Preu, 1967), W, P 872. -rtIomu Ford, "The Dawn of Navigation and its Books Theories and Iutrumtmt.," 1906 'Proceuinga 01 the UnUed Statu Naval lnatitvts Vol.. ume xxxn (AnnapoU8: United States Naval Institute, 1906), P 274.