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:— ---------------------+-----------+-----------+------------- | Berenice |St. John’s |Halaib Fort. | Temple. | Peak. | +-----------+-----------+------------- Admiralty Chart |35° 28′ 31″|36° 10′ 20″|36° 37′ 3″ | | | “Pola” Expedition |35° 29′ 26″|36° 13′ 13″|36° 40′ 38″ | | | Ball (Triangulation)|35° 28′ 26″|36° 11′ 42″|36° 38′ 56″ ---------------------+-----------+-----------+------------- There can, of course, be no doubt of the immensely greater accuracy of the triangulation method of determining longitude as compared with that of chronometer transport in voyages lasting for months, no matter how many chronometers are carried nor what care is taken in the work. The above differences of longitude are small when one considers that no absolute control of the chronometer of the “Pola” expedition was obtained from October 23, 1895, when the ship left Suez, till its return to the same port on January 27, 1896. If we examine the difference of longitude between points fairly close together, we find rather better agreement between chronometers and triangulation. Thus, for instance, between Berenice and Halaib, a six days’ voyage, we have:— --------------------+-------------+-------------- |Longitude by |Longitude by |Chronometers |Triangulation | (Koss). | (Ball). +-------------+-------------- Halaib Fort | 36° 40′ 38″ | 36° 38′ 56″ | | Berenice Temple | 35° 29′ 26″ | 35° 28′ 26″ +-------------+-------------- Difference | 1° 11′ 12″ | 1° 10′ 30″ --------------------+-------------+-------------- showing an error of only 42″, or about three seconds of time in the six days. The triangulation-positions:— ------------------+-------------+-------------- | Latitude N. | Longitude E. +-------------+-------------- Berenice Temple | 23° 54′ 39″ | 35° 28′ 26″ | | St. John’s Peak | 23° 36′ 16″ | 36° 11′ 42″ | | Halaib Fort | 22° 13′ 25″ | 36° 38′ 56″ ------------------+-------------+-------------- may therefore be taken as practically correct, and the three points may be used as well-determined positions both for further discussion of the “Pola” results and in further surveying expeditions in the Red Sea.[75] =Detail Surveying along Lines of March.=