THE Museum has acquired a copy of one of the most impressive books on astronomical instruments to appear in the eighteenth century, Pierre-Charles Le Monnier’s Description et usage des principaux instruments d’astronomie, published in Paris in 1774.
Le Monnier, a practical astronomer, had been a member of the famous geodetical expedition of 1736 to Lapland, with Pierre-Louis Moreau de Maupertuis and Alexis Claude Clairaut. The equipment of the expedition included a 9-ft zenith sector, a transit instrument and a clock, all by George Graham, the leading English maker of the day. Maupertuis’ subsequent publication, Le figure de la terre (Paris, 1738), with its detailed account of the sector, was an important stage in establishing the international reputation of the London school of precision instrument making founded, in effect, by Graham.
Le Monnier published his Histoire céleste in 1741, as a review of observations made in France since the founding of the Académie. The transit instrument he describes there and illustrates in detail was also by Graham, and Le Monnier introduces his Description by relating it to his own previous account of the transit instrument, to Maupertuis’ account of the zenith sector, and to the general textbooks written by Nicolas Bion in France and Robert Smith in England.
What Le Monnier believes to be new, and to call for a new treatise on astronomical instruments, is the growing importance of the mural quadrant, which he thinks is capable of being a universal instrument for all fundamental measurement in astronomy.
Le Monnier was intimately familiar with the English mural quadrant, having acquired one of 5ft 4in radius from Jonathan Sisson in 1743. He had also examined the original Graham quadrant in detail at Greenwich in 1748, and obtained a similar instrument of 8-ft radius from John Bird in 1753. He had lent his smaller quadrant to the Berlin Academy in 1751, sending along his student Joseph Jérôme le Français de Lalande to advise on setting it up. As the Description was being prepared for publication, Lalande himself was arranging the purchase of a further 8-ft quadrant from Bird. At the same time Bird was at work on two 8-ft quadrants for the Radcliffe Observatory, one of which is now in the Museum.
It was clear that, as the mural quadrant was becoming the principal instrument in the observatories of Europe, so London makers were moving into a position where they dominated the market in precision instruments. Le Monnier played an important part in this process, especially in relation to France, and his Description is one of its most impressive monuments. In his introduction he sought to link Paris and London at the head of recent progress, but in the body of the work he was, in effect, acknowledging the growing authority of the London makers: ‘Comme Paris & Londres sont les deux Capitales de l’Europe où les Arts sont poussés au plus haut degré d’étendue, & qu’ils sont favorisés par le plus grand commerce de ces deux Villes, nous devons à l’industrie de quelques hommes rares & profonds Méchaniciens les succès rapides & les progrès étonnants, auxquels on a porté les Instruments d’Astronomie.’
The British Board of Longitude had already published two tracts by John Bird on constructing such instruments and on dividing their scales. Bird, however, had been content to include three plates in his quarto-format tract on construction and only one in the tract on division. Le Monnier insists that three or four times as many illustrations are required for the necessary level of detail, and he includes fourteen magnificent folding plates in his oversized folio volume.
The quality of the illustrations, executed with great clarity and skill, and in particular the precise attention to detail in representing the individual components, was unprecedented in publications on instruments. To achieve this Le Monnier engaged two of the most experienced technical illustrators of his day – the draughtsman Louis-Jacques Goussier and the engraver Robert Bénard – both of whom had worked extensively on the famous Encyclopédie of Diderot and d’Alembert.
Goussier, described as a mathematician in the Dictionnaire de biographie française, had travelled widely in the course of preparing over 900 drawings for the Encyclopédie, and was fulsomely complimented by Diderot for his work. Following the completion of the Encyclopédie in about 1768, a variety of commissions followed, including work for the Conservatoire nationale des arts et métiers after the Revolution.
The qualities evident in the plates of the Encyclopédie are present also in those of Le Monnier’s Description. The illustration above shows an 8-ft quadrant by Bird almost identical to the instrument in Oxford, except that Le Monnier has it mounted on a rotating section of wall, so that it can face north or south. The resulting instability, however, meant that this innovation was not a success and was not adopted elsewhere. J. A. B. / A. V. S.