| Observer. | Date. | Observed Declination W. | Yearly change. | |
|---|---|---|---|---|
| Cailliaud | January 1820 | 12° | 13′ | |
| Jordan | March 1874 | 6° | 33′·6 | 6′·3 |
| Lyons | April 1894 | 5° | 8′·9 | 4′·2 |
| Geological Survey | December 1897 | 4° | 50′ | 5′·3 |
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:—
| Date and Time. | Zubbo. Bar. (corrected). | Cairo. Bar. (corrected). | Difference. | ||
|---|---|---|---|---|---|
| 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 | ||||
Since 1 mm. of mercury corresponds at the mean temperature of observation (20° C.) to 11·4 metres of height, we have height of Zubbo camp above Cairo observatory = 8·32 × 11·4 = 94·7, or say 95 metres. Since the observatory is 33 metres above sea-level, the camp at Zubbo is 128 metres above sea-level. Jordan’s altitude for Bawitti, which probably lies at about the same level as Zubbo, is 113 metres, and when it is remembered that the point of the Survey’s observation lay not in Zubbo itself, but at the camp on elevated ground some 10 or 12 metres above it, the results show a very good agreement.
At Ain el Haiss three barometric observations were taken on different days; the comparison of these with the Cairo records would place this point 156 metres above sea-level. Jordan’s value is 122 metres, the number of observations on which this figure is based not being stated, it is difficult to say which of the two altitudes is the more probable.
At the remaining camps within the oasis, and at the camps en route between the oasis and Minia, corresponding observations were taken, the number of comparisons with Cairo varying from two to seven at an individual station. These observations being reduced and corrected by comparison among themselves gave the levels of the different camps with some degree of approximation to accuracy, and the altitudes of intermediate points were found by interpolation based on barometric readings. The resulting altitudes will be found on the map ([Plate I]); where no altitudes have been taken by the Survey, the values given by Ascherson on his map have been inserted.
The statistics relating to the oasis, and the methods of cleaning out wells, are based on information supplied by the Government officials at Bawitti, and may be taken as fairly reliable. The particulars regarding water-supply are of course based mainly on direct observation during the survey of the villages.
The botany of the oasis having been fully studied by Ascherson[13] no attempt was made by the Survey to collect or describe the plants met with. The abundant growths of the beautiful maiden-hair fern (Adiantum Capillus Veneris)[14] will not, however, fail to strike even the casual visitor to the old Roman aqueducts, which still serve as the principal water-channels of the oasis. Nor were the animals of the oasis made the subject of any detailed observations, although the existence of several of the species of lizards and snakes common to the Nile Valley was recorded, and specimens collected when easily obtainable.
Baharia is not rich in archæological remains, and, with few exceptions, even those existing were not examined by the Survey, though the positions of all ruins met with during the work were mapped. In a later chapter will be found a connected though brief account of all the antiquities noted, the publications of previous authors being referred to wherever the descriptions cannot be given from personal observations.