Page:History of the Royal Astronomical Society (1923).djvu/256

 224 HISTORY OF THE [1880-1920 of the British triangulation rendered a remeasurement desirable, it would be well to measure a base and remeasure a portion of the old triangulation remote from the principal bases at Salisbury Plain and Lough Foyle, in order to ascertain in a previously untested region what linear errors had accumulated. This was approved by the Council of the Association, and on its recommenda- tion the Board of Agriculture and Fisheries authorised the Ordnance Survey to undertake the work. It was carried out in the years 1909 to 1912, and consisted in the measurement of a base on the southern shore of the Moray Firth, east of the town of Lossie- mouth, and a test triangulation in Morayshire.* The investiga- tion of these measurements showed that the linear errors of the old net-work triangulation of the United Kingdom are in the same terms as those to be expected in modern triangulation carried out in chains over similar distances. The error to be expected may be said to be of the order of one inch in one mile. The dis- cussion showed that the excellent agreement between the measured and computed values of the bases at Lough Foyle and Salisbury Plain was not accidental, but is confirmed by the inter-comparisons of these bases with those measured at Paris and at Lossiemouth. These comparisons give results which are in some cases better and in some cases worse than those derived from modern work in Europe, India, South Africa, and the United States. The influence on modern figures of the earth of any remeasurement of the British arcs would be insignificant. In 1907 a large surveying party was making a topographical survey of the area north of the German territory in Central Africa, near the Equator, along the 30th meridian. In April of that year Gill wrote to the Council that it was very important to retain this party for four months longer, in order to make a reconnaisance for the measurement of a geodetic arc of 2^ along the 30th meri- dian, forming part of the great African arc. The Berlin Academy had approached the German Government for funds to continue the arc east of Lake Tanganyika, which proposal (Gill suggested) would be much strengthened if it could be shown that work had been commenced north of the German territory. It was therefore proposed that the Council should give 50, to be added to 950 from the Royal Geographical Society, the British Association, and the Royal Society, after which the Government would be asked for another 1000. This was willingly agreed to by the Council. Eventually it turned out that owing to unfavourable weather the cost was nearly twice as great as estimated, and the Council in 1910 paid 25 towards covering the deficiency. 1912-13, 4.
 * Ordnance Survey, Professional Papers, new series, Nos. i and 2. London,