Biography of José de Mendoza y Ríos (1762-1816)

Military Spanish born in Seville in 1762 and died in Brighton (England) in 1816. Navy officer, was educated at the Royal Seminary of Nobles of Madrid, and in 1789 entrusted the Mission of acquiring books in London for the Ministry of the Navy. In that city he made friends with English scientists and was elected member of the Royal Society in 1793. He made several services as scientific intermediary with England, in 1796 did submit to the consideration of the Ministry of State a catalogue of maps published in England and Ireland, as well as the negotiation and purchase of a Herschell's two feet in diameter for the Observatory of Madrid. A collection of scientific books to the Depósito Hidrográfico sent from England in 1798. Serving as liaison between the Spanish Navy and the English makers, Mendoza, who had widely complained of the practicones without scientific knowledge producing compasses and similar instruments, remained firm in their insistence on the need to professionalize the manufacture of nautical instruments.

The most famous contribution of Mendoza to navigation refers to the procedure to "clear the distance", the most laborious aspect of the determination of lengths by the lunar method. To perform an accurate reading is to clear "the apparent distance of the effects of Parallax and refraction in order" to determine the angle from the center of the Earth between the directions of the center of the Moon and the center of a star, a planet or the Sun. There were many rival methods: Mendoza describes forty in his article in 1797 in the Philosophical Transactions. Mendoza's own contribution lies in comprehensive tables and an instrument (a reflection circle), measuring the length of the southern arc. Tables of Mendoza, about half are directed to the problem of clearing the lunar distance, with values for each minute of arc. His 1802 tables included other correction that combined the values for refraction and Parallax of the Moon, constituting an original and saving innovation.

In 1801 he sent the manuscript to English Board of Longitude waiting to ensure financial support for the publication. In this company, he obtained the help of the President of the Royal Society, Joseph Banks, to which dedicated the second edition of the tables; Company was finally borne by the British Admiralty, the Board of Longitude and the East India. Reflection circle was the problem that most interested to Mendoza. A notable limitation of nautical instruments was that these instruments had to be held with the hand and smaller was the greatest instrument was its inaccuracy. According to Mendoza, the large instruments were useful in practical astronomy, because they allowed "the observer read angles according to a small fraction of a degree, as well as decrease in construction inaccuracies from errors of the divisions and the eccentricity of the index".

Tobías Mayer had greatly improved the circle of reflection. His circle was more accurate than the previous ones because, instead of reading a simple angle reading a multiple of this. But it was difficult to use because it required repeated observations to produce two parallel images. The circle of Mayer had been improved in turn by Jean-Charles de Borda, who set the telescope to the alidade. Mendoza added the Borda circle a second arch, concentric to the original. "He was graduated and joined the alidade which is carrier of the small mirror; on this circle could be slipping two small pieces that were kept fixed thanks to certain Springs, which could be quickly bring two objects to the field of vision"(García Franco). Totally an advocate of modern scientific currents, Mendoza accepted the Copernican Cosmology and Newtonian physics.


Articles and publications of José de Mendoza y Ríos:

Treaty of navigation, 2 vols., (Madrid, Imprenta Real, 1787).

Report on some new methods of calculating length by Lunar distances, (Madrid, Imprenta Real, 1795).

Recherches sur les principaux problèmes de l'astronomie antique", Philosophical Transactions, no. 87, pp. 43-122, (1797).

Collection of tables for various applications of navigation, (Madrid, Imprenta Real, 1800).

On an Improved Reflecting Circle", in Philosophical Transactions, no. 91, pp. 363-374, (1801).

Tables for Facilitating the Calculations of Nautical Astronomy, (London, Wilson, 1801).

A Complete Collection of Tables for Navigation and Nautical Astronomy, (London, T. 86th, 1805); 2nd ed., (1809).

Translation of the explanation, problems and examples of the 2nd ed., Don José de Mendoza y Ríos, ed. dir. nautical tables by Antonio Martínez and heel, (San Fernando, Royal Guard company marine, 1815).R. DAWSON, Warren: The Banks Letters, ed. dir. by London, p. 604, (British Museum, 1958). G. FLORBES, Eric: Index of the Board of Longitude Papers at the Royal Greenwich Observatory, in Journal for the History of Astronomy, nº 2, pp. 64, 134 and 138, (1971).


H. COTTER, Charles: A History of Nautical Astronomy, (London, Hollis and Carter, 1968).GOODWIN, Gordon: Joseph de Mendoza y Ríos, Dictionary of National Biography, vol. XIII, p. 251, (London, Oxford University Press, 1949-1950). Reimpresion.mascart, Jean: La vie et les travaux du chevalier Jean Charles de Borda (1733-1799), pp. 244 and 376-380, (Lyon, 1919).Garcia FRANCO, Salvador: History of the art and science of sailing, vol. I, p. 258, (Madrid, historical Institute of marine, 1947).

Thomas F. Glick