It is interesting to compare the positions found for certain triangulation points with those determined by the British Admiralty surveyors and by Lieut. Koss, who accompanied the Austrian research-ship “Pola” in 1895-6.[74] The three best defined points of comparison are Berenice temple, the central peak of St. John’s Island, and Halaib Fort. In the case of Berenice and St. John’s Island the observation of the two prior surveys were made at stations a little distance from my triangulation points, but the published charts enable one to scale off the necessary corrections to reduce the positions to those of the triangulated points. At Berenice, the British Admiralty observation point, for which the latitude is given as 23° 56′ 16″, is 1′ 26″ north of the temple, so that the equivalent Admiralty latitude for the temple is 23° 54′ 50″. Similarly Lieut. Koss’s observation point, where the latitude found was 23° 56′ 27″, is 1′ 47″ north of the temple, giving the latitude of the temple as 23° 54′ 40″. My triangulation gives the latitude of the temple as 23° 54′ 39″, thus showing a remarkably good agreement with that found by the “Pola” observer.
At St. John’s Island, owing to the smallness of the scale of the available charts, it is a little more difficult to scale off accurately the Admiralty position for the peak and the reduction to the peak of Lieut. Koss’s point. As nearly as I can scale, the Admiralty latitude for the peak is 23° 36′ 40″, while the point where Lieut. Koss observed his latitude of 23° 35′ 47″, near the south-west shore of the island, is approximately 40″ south of the peak, giving the latitude of the peak as 23° 36′ 27″. I found the latitude of the peak to be 23° 36′ 16″, thus again showing as good an agreement as could be expected, having regard to the fact that it is not easy to scale the latitude of the point much within 10″ from the existing charts.
At Halaib Fort, the Admiralty latitude is 22° 14′ 10″, while the “Pola” expedition found it 22° 13′ 26″, and my triangulation gave the value 22° 13′ 25″. The close agreement between my triangulation value and that observed by Lieut. Koss seems to prove the Admiralty latitude of this point to be some 45″ too high.
Summarizing the latitudes of the three points for comparison we have:—
| Berenice Temple. | St. John’s Peak. | Halaib Fort. | |
|---|---|---|---|
| Admiralty Chart | 23° 54′ 50″ | 23° 36′ 40″ | 22° 14′ 10″ |
| “Pola” Expedition | 23° 54′ 40″ | 23° 36′ 27″ | 22° 13′ 26″ |
| Ball (Triangulation) | 23° 54′ 39″ | 23° 36′ 16″ | 22° 13′ 25″ |
If we make corresponding comparisons of the longitudes of these three points, Berenice Temple, St. John’s Peak, and Halaib Fort, we obtain much more wide divergences, as is only to be expected from the fact that the Admiralty and “Pola” determinations were made by transport of chronometers from Suez, which is over 500 miles distant from Halaib.
For Berenice Temple the Admiralty longitude (obtained by applying the scaled reduction of − 40″ to the observed longitude 35° 29′ 11″ at the observation point) is 35° 28′ 31″. Lieut. Koss’s transport of chronometers from Suez via Jidda leads to a longitude of 33° 30′ 20″ for his observation point, which lies 54″ east of the temple; thus the “Pola” longitude for the temple is 35° 29′ 26″. My triangulation gives 35° 28′ 26″, thus agreeing very nearly with the Admiralty value and differing by exactly 1′ from the value found by Lieut. Koss.
For St. John’s Peak, the longitude scaled from the Admiralty Chart is 36° 10′ 20″. The observations of Lieut. Koss lead to a longitude of 36° 12′ 38″ for his observation point, which is about 35″ west of the peak; thus the “Pola” longitude for the peak is 36° 13′ 13″. My triangulation gives 36° 11′ 42″, being thus between the Admiralty and “Pola” values.
For Halaib Fort, the Admiralty longitude is 36° 37′ 3″, while Lieut. Koss’s figures lead to the value 36° 40′ 38″; my triangulation gives 36° 38′ 56″, thus again showing a value between the two marine determinations.
Summarizing the longitudes obtained for the three points, we have:—