The Problem of Double Longitudes on Glavač’s Map

Abstract

Stjepan Glavač (1627-1680) produced a map of Croatia dated 1673, on which two meridians appear twice, 40°/51° and 41°/52°. The only written source regarding Glavač’s map is the dedication, which forms an integral part of the map. It does not say which prime meridians Glavač relied on, so in our research we attempted to establish what those prime meridians might have been. We approached the problem of the double longitudes using linear regression, through which we wanted to examine the relation of Glavač’s longitudes to modern values. An essential part of the research was a comparison of Glavač’s map with maps by his predecessors and contemporaries which show approximately the same prime meridians. The maps analysed, with their written values for the longitudes of certain places, indicated that the selection of prime meridians at that time was not entirely reliable. A further problem seemed to be the knowledge of the position of islands chosen as points of departure for longitudes. We concluded that the points of departure for Glavač’s dual longitudes were Palma, one of the Canary Islands, and the islands of Corvo and Flores in the Azores.

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