Compendio del arte de navegar (Seville, 1588): Copernicus cited in the pilots' textbook of the Indies run
The textbook that trained and examined the pilots of the Indies run, by the holder of the chair of cosmography at the Casa de la Contratacion, styled piloto mayor on this title page too. Its address to the reader declares the solar declination table of every earlier manual wrong, gives two reasons, names Peurbach, Regiomontanus, Werner, Copernicus and Reinhold for the second, and reports the author's own measurement at Seville.
Why this wins its question: The question of whether Copernicus was read in sixteenth-century Spain is usually answered from university statutes or from the Index, and the answer offered is atmospheric. This object answers it from a page: a state navigation textbook printed at Seville in 1588, written by the holder of the chair that examined the pilots of the Indies run, which names Copernicus in a list of authorities for a measured quantity and then reports the writer's own instrument reading from Seville beside theirs. Around that it gives what the general accounts leave out - that the book opens by declaring the standard solar table of the trade wrong; that it explains the error from the eleven minutes by which the civil year misses the true one and derives a rule that the table must be recomputed every sixteen years; that it teaches a pilot to audit his own chart with a pair of dividers, four degrees of the graduation against seventy leagues of the scale; and that it lists latitude for every shoal and bank while quietly leaving longitude out of what a chart can tell. It also prints, in its licence, the whole apparatus of monopoly, correction against a signed original, compulsory errata and fixed price that a Spanish technical book had to pass through.
Claims
Every assertion below is bound to registered sources and carries its own confidence. Weight them; do not treat the page as uniformly authoritative.
The title page states the book, the offices of its author and the imprint. It reads "COMPENDIO DEL ARTE DE NAVEGAR, del Licenciado Rodrigo Camorano, Cosmografo y Piloto mayor de su Magestad. CATEDRATICO DE Cosmografia en la casa dela Contratacion de las Indias", with a printer's device between two medallions, and below it "CON PRIVILEGIO. IMPRESSO EN SEVILLA en casa de Ioan de Leon. Año, 1588." The author is therefore presented as holding at once the crown's cosmographer's post, the office of chief pilot, and the salaried chair that taught and examined the pilots of the Indies run - the teacher, the examiner and the standard-setter in one man.
The address to the reader opens by condemning the tables in every earlier manual, including the ones the pilots were using. "No puedo dexar de dar cuenta, curioso Lector, de algunas cosas muy importantes que en abriendo este Regimiento, o Arte de Navegar, encontrareys harto diferentes de las que ponen otros libros de este mismo argumento, si comparardes esta mi obra con las que hasta aqui se an escrito: de las quales es una principalissima la tabla de la declinacion del Sol, que por dos causas hasta aora en todos los Regimientos de la navegacion a ido errada, y fuera de toda verdad." A working textbook begins by telling its readers that the most-used table in the trade is wrong.
The first reason is the drift of the civil year, and it is given with numbers and a maintenance rule. Because the mean year "no sea mas que de 365. dias y cinco horas y 49 minutos", while the ordinary reckoning of years adds six full hours beyond the whole days, those eleven minutes of difference between the reckoning and the true motion of the Sun are the cause "que en los Equinocios aya variado medio grado en cada ochenta años". From that the book draws a practical consequence: "es cosa muy necessaria, que la tabla de las declinaciones del Sol se haga de nuevo cada 16. años, en que por la diferencia de nuestros años a los del Sol, se varia la declinacion por tres minutos acerca de los Equinocios." A sixteen-year revision cycle for a published table, stated as a rule, in a book for seamen.
The second reason cites the European astronomical literature by name - Copernicus among it - and then reports the author's own measurement. "Porque el dia de oy, en la mayor declinacion del Sol ay algunos minutos menos, de los que demas de los grados solia aver en tiempos passados: como lo an hallado Georgio Purbachio, Iuan de Monte Regio, Vvernero, Copernico, Erasmo Reynoldo y otros doctissimos y muy diligentes Matematicos de nuestros tiempos: y lo avemos tambien observado, con instrumentos harto capaces aqui en Sevilla, y otras partes, no passar de 28. minutos demas de los grados enteros." Peurbach, Regiomontanus, Werner, Copernicus and Reinhold stand together as observational authorities in a Spanish state textbook printed in 1588, and the obliquity of the ecliptic is given from Seville instruments as twenty-three degrees and twenty-eight minutes. The claim being made of Copernicus here is about a measured quantity, not about the motion of the earth, and this corpus asserts no more than that.
The book's opening page divides the subject in a way that puts theory first and makes it compulsory. "Toda la Arte con que se navega por derrotas y alturas, se divide en dos partes principales, Teorica, y Pratica. La Teorica da el conocimiento de la compostura de la Esfera del mundo en general: y en particular enseña el numero, figura y movimientos de los cielos, principalmente del primer mobil, noveno, octavo, quarto, y primer cielo: la figura, cantidad y sitio de los Elementos, principalmente tierra, y agua: y los circulos que en esta Esfera se imaginan, sin cuyo conocimiento es impossible navegarse. La pratica enseña la fabrica, composicion y uso de los instrumentos que en la navegacion sirven, qual es el Astrolabio, Ballestilla, Aguja, y Relox, con el regimiento del Sol y de la Estrella, las reglas de la Luna y delas mareas, y la declaracion de la carta." The cosmology taught is the received one of nested heavens; the insistence is that no one can navigate without it.
The chapter on the sea chart teaches a pilot to audit the chart he is given, which is a different thing from teaching him to read it. Among the checks: that the wind-lines are truly drawn, verified with the compasses, "mirando con el compas que los agujones todos este en igual distancia unos de otros, y que todas las lineas que representan un solo rumbo, estan paralelas unas de otras"; that in the graduation the degrees are equal in all its parts and the parts of the earth correspond east and west to the degrees each thing stands in; and that the scale of leagues agrees with the scale of degrees, tested by taking four whole degrees of the graduation line between the points of the compasses, which carried to the trunk of leagues "an de ocupar en el 70. leguas justas". Seventeen and a half leagues to the degree, checkable by any pilot with a pair of dividers.
The same page states what a chart is for, in five items. "Por la carta de Marear se conocen cinco cosas. La primera es la disposicion y arrumbamiento de las costas. La segunda, las distancias y leguas que ay de unas a otras. La tercera, los grados de altura, o apartamiento de la Equinocial, en que esta cada tierra, assi firme como Isla, puerto, rio, Isleo, baxo, o banco. La quarta el rumbo, o rumbos por donde se a de navegar, de una parte a otra. La quinta es el punto y lugar donde estamos con nuestra nao, quando navegamos." Latitude is listed for every feature including shoals and banks; longitude is not among the five, which is a fair statement of what the charts of the carrera could and could not do.
The printing was licensed as a monopoly with a checking procedure attached. The royal cedula bound in front grants Zamorano licence and faculty for ten years from its date, during which nobody else may print or sell the book in those kingdoms; it requires that the printing be brought before the Council together with the rubricated original signed by the escrivano de camara Christoval de Leon, "para que se vea si la dicha impression esta conforme a el", or else a public certificate that a corrector named by royal order saw and corrected it against the original; that the errata be printed in every copy; and that the price be tassed. The penalty on an unlicensed printer or seller is loss of the books, moulds and equipment plus fifty thousand maravedis, divided in three - a third to the royal chamber, a third to the denouncer and a third to the judge who sentences. It is dated San Lorenco, 22 September 1584, and countersigned "Por mandado de su Magestad. Antonio de Erasso." The Seville printing of 1588 falls inside that ten-year term.
The copy digitised here carries its own small history on the title leaf. A contemporary ink signature runs across the upper right of the page, and at the foot a later hand has written in pencil "Robert Southey. Keswick. Dec 25. 1810." A pilots' manual printed at Seville in 1588 for the Indies run was in the hands of an English poet in the Lake District two and a quarter centuries later. This corpus records the inscription as it stands on the page and asserts nothing further about the copy's route there.
What this object does not establish should be stated as plainly as what it does. Only the pages listed in the source entry were opened: the title, the privilege, the address to the reader, the first folio, and folio 59 on the sea chart. The declination tables themselves - the thing the address to the reader is chiefly about - were not read, so the assertion that they were recomputed rests on the author's statement rather than on inspection of the tables. The rules of the moon and tides, the chapters on the instruments, and the close of the book were not seen. The earlier Seville printing of 1581 was not opened, so nothing is claimed here about what changed between the two, and nothing about the book's editions and translations outside Spain, which are not attested by anything read for this object. Nor does this corpus assert that Zamorano's figure for the maximum solar declination was correct, only that he printed it and said he had measured it at Seville.