1. Introduction
THE cartographical data brought back by Hassanein Bey consist of:
(1) Note-books containing the records of astronomical observations for the determination of time, latitude, and compass-variation at nineteen principal camps, with records of watch-comparisons.
(2) A journal giving a continuous record of observed compass-bearings and estimated distances from Siwa Oasis to Lameina Wells, near El Fasher, a distance of about 2430 kilometers.
The journal also contains a considerable number of observed compass-bearings to conspicuous features on either side of the route, with a few rough trigonometrical estimations of the altitudes of mountains passed, a large number of readings of an aneroid barometer and sling thermometer for the estimation of altitudes along the route, daily observations of maximum and minimum temperatures, observations on the character of the country passed through, and notes on the meteorological conditions.
These observational data have been reduced in the Desert Survey Office, Cairo, and utilized in the preparation of the map on a scale of 1:2,000,000 which accompanies Hassanein Bey’s account of his travels. The objects of the present note are, first, to give an account of the critical examination to which the records were subjected in the course of the reduction of the observations, so as to enable an estimate to be formed of the degree of precision which may be fairly assigned to the geographical positions, altitudes, and other results used in the construction of the map; and, secondly, to indicate the additions to existing geographical knowledge concerning a little-known region of northeast Africa which have accrued from the expedition.