Careful observations were made of the variation of the compass at three stations, _viz._, Berenice Temple, Abu Saafa Springs, and near Halaib Fort,[80] these three points being selected as being well-known places and at the same time likely to be free from local magnetic disturbance. Berenice is on the coast-plain where only coral and sand occur; Abu Saafa is in a sandstone district about 100 kilometres south-west of Berenice, and Halaib is on the calcareous and gypseous rocks of the coast about 220 kilometres south-east of Abu Saafa. The instrument used was a five-inch theodolite fitted with a good trough compass. A lens was used to bring the needle accurately to zero, and the sun or a star was employed to find the true meridian. In each case several observations, each with an independent setting of the needle, were made, and the mean taken. The values obtained were:— -------------------+---------------------------+------------------ Place. | Date and Time. |Compass-Variation | | West. -------------------+---------------------------+------------------ Berenice Temple |January 6, 1907, 5·30 p.m. | 2° 44′ | | Abu Saafa Springs |October 25, 1907, 4 p.m. | 2° 37′ | | Near Halaib Fort |May 7, 1908, 10 a.m. | 2° 18′ -------------------+---------------------------+------------------ In order to find to what degree of accuracy the results of these determinations might be relied on, the instrument used was tested against the Kew magnetometer at the Khedivial Observatory, Helwân, after the completion of the work. Three observations for the declination at Helwân gave the westerly variation as 2° 41′·2 2° 58′·8 2° 55′·0 -------- Mean 2° 55′·0 -------- while the true declination as given by the Kew magnetometer at the same time was 2° 52′ 5″. Thus it appears reasonable to believe the observed values to be within about 5′ of the truth. It is rather curious to note that the declination observed at Abu Saafa is less than that at Berenice, which lies further east, even if allowance is made for the secular change in the interval. The difference from what one would expect is, however, possibly owing to errors of observation of the magnitude above-mentioned, or it may be due to a slight local influence of magnetic rocks underground at Abu Saafa, where the ground is near to the base of the Nubian sandstone beds, which rest presumably on eruptive and metamorphic rocks. It is interesting to compare the observations of declination at Berenice and Halaib with those recorded by ROSSLER[81] at the same places in 1895. Thus we have:—