frontier, a view is commanded in clear weather of the crests of the sierras on the opposite coast of Spain, at a distance of no less than 168 miles. It thus became possible to connect the network of Algerian triangulation with that of the Iberian peninsula without passing through Marocco. The four points chosen for the connecting quadrilateral were Mulhacen in the Sierra Nevada, Tetica in the Sierra de los Filabres, at the south-cast angle of the peninsula, Filhausen in the Trara
range, and Msabiha in the neighbouring Oran group. The chain of triangles is now continuous from the northernmost islet in Shetland to the 34th parallel of latitude in Algeria, and will soon be extended far into the Sahara, forming the largest are of the meridian that has hitherto been astronomically measured on the surface of the globe.
