A wooden backstaff (or Davis quarter) unsigned made in England circa 1750.

A wooden backstaff (or Davis quarter) unsigned made in England circa 1750.



Lenght 65 cm.



Country of manufacture

UK and Ireland

Categories: Maritime, Navigational instruments


A wooden backstaff (or Davis quarter) unsigned, composed of two arcs: the sight vane arc is numbered 0-25° and 65-90°, the smaller arc is divided into 62°.

Facing the Sun, it indicates its height above the horizon, but the originality of the instrument was to obtain the same result using it backwards. The lens added on the sliding sight of the little arc was imagined around 1770 in order to be used in case of cloudiness.

Under optimum conditions the accuracy was up to 1/10th of a degree!

Literature: « Marine Antiques – a Chronicle of a Unique Collection – Dominique Delalande –New York 1986 » The calculation of latitude pp 2 & 3. « L’instrument de marine » – Jean Randier p 119.

NB: nearly always missing, the vane and sliding sights in boxwood have been replaced and recalculated later.

Dimensions: length 65 cm – width 37 cm.

England 1750/1760.


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FR Galerie Delalande Paris

After 37 years in Le Louvre des Antiquaires, the Delalande gallery moved early June 2015 to 35 rue de Lille, 75007 Paris, on the other side of the Seine River in the well known antic shops area "le Carré Rive Gauche".
Our main specialties are, since 1976, Marine and Scientific instruments, Tobacco and Opium objects, Curiosities and Great Canes.
We participate to international antique fairs (TEFAF Maastricht) and are unique partner of the French Maritime Museum.
Eric Delalande is also Administrator of the French Experts National Company (C.N.E.).
Please visit also our two websites, which are frequently updated: www.antiquites-delalande.fr (French) and www.delalande-antiques.com (English). ----------------------------

La Galerie Delalande s'est installée en juin 2015 au 35 rue de Lille (75007 Paris), au coeur de la capitale dans le "Carré Rive Gauche", après 37 années de présence au Louvre des Antiquaires.
Nous nous sommes orientés, depuis 1976, vers plusieurs spécialités : Marine et Sciences, Objets du tabac et de l'Opium, Cannes de collection et Curiosités.
Nous participons à des salons d'envergure internationale (TEFAF Maastricht) et sommes partenaires exclusifs du Musée National de la Marine.
Eric Delalande est également Administrateur de la Compagnie Nationale des Experts (C.N.E.).
N'hésitez pas à visiter nos deux sites internet fréquemment mis à jour : www.antiquites-delalande.fr (Français) and www.delalande-antiques.com (Anglais).

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