In view of the magnitude of the diurnal variation, which may range up to 10′ of arc, and our present lack of knowledge of the distribution of this diurnal variation during the twenty-four hours, a comparison after so short an interval as that between the last two observations is not to be trusted. It would seem proved from the three foregoing observations that the yearly variation is at present decreasing, the mean from 1820 to 1874 being 6′·3 as against 4′·2 for the period 1874-1894. This decrease is also noticeable in comparisons of the declinations observed at different times in other parts of Egypt. The _altitudes above sea-level_ of the principal points, more especially in the eastern half of the oasis, were determined with a Watkin aneroid barometer, which had been compared with the Cairo standard mercurial barometer. A fairly long stay was made at the Zubbo camp, and the altitude of this point may be regarded as fairly accurately fixed by the observations tabulated below:— -----------------------+-------------+--------------+--------------- | Zubbo. | Cairo. | Date and Time. | Bar. | Bar. | Difference. |(corrected). | (corrected). | -----------------------+-------------+--------------+--------------- | mm. | mm. | mm. | | | October 12, 6 p.m. | 753·54 | 761·10 | 7·56 | | | „ 14, 8 a.m. | 754·94 | 763·04 | 8·10 | | | „ 6 p.m. | 753·79 | 761·53 | 7·74 | | | „ 15, 7.30 a.m. | 754·55 | 762·60 | 8·05 | | | „ 9 p.m. | 754·30 | 762·64 | 8·34 | | | „ 17, 7.15 a.m. | 754·18 | 761·84 | 7·66 | | | „ 18, 7 a.m. | 753·79 | 761·64 | 7·85 | | | noon | 752·52 | 761·34 | 8·82 | | | „ 19, 8.30 a.m. | 752·65 | 762·31 | 9·66 | | | Nov., 26, 3 p.m. | 754·81 | 763·29 | 8·48 | | | „ 27, 8 a.m. | 754·81 | 764·12 | 9·31 -----------------------+-------------+--------------+--------------- Mean | 8·32 --------------------------------------------------------------------