Page:The journal of the Royal Geographic Society of London. Volume 34, 1864. (IA s572id13663720).pdf/287

Rh the Reconnaissance Survey of 1857-8. The Wakaia district has been plotted on the map of the south-eastern districts with reference to the positions of the Pyramid and East Dome, as laid down on it by Mr. Garvie. The altitudes are relative to the Black Umbrella, 3580 feet above sea-level, also determined by Mr. Garvie.

The distances throughout the survey were determined from bases measured twice by a common chain; artificial marks were set up till a length of 3 or more miles was obtained in the sides of the triangle, after that natural marks, such as mountain-peaks, edge of landslips, &c., were used as points for triangulation; where this was impracticable, then the method of converging angles was had recourse to. Up the Fiords of the Te Anau and Manipori Lakes, where, on account of the inaccessible nature of the mountains, and the shore-line being shaded over with foliage, neither a triangulation could be carried on, nor bases measured, differences of level between the lake and one or more commanding peaks were used as a base for determining distances. This method, from the rapidity it gave to the execution of the work, was found to be of great value under the circumstances. There was generally no difficulty in finding a suitable mountain-peak, a mile or so in vertical height above the level of the lake; the angle of elevation to which, after the necessary corrections had been applied, giving an excellent means of determining distances up to 7 or 8 miles. The bearings were (from the same reasons as rendered a vertical triangulation necessary) magnetic. Care was always taken on returning to the stations of the true meridian to observe if there was any local deviation in the variation of the compass. In every other part of the survey the work was done on the true meridian. The difference of bearing between the meridians of Mount York and Mount Nicholas was found to be 30'; the difference to be added to the meridian of Mount Nicholas. The difference of bearing between the meridians of Mount Nicholas and Lindis Peak 44', the difference to be added to the meridian of Lindis Peak. These differences are not to be taken as precise, seeing that the instrument had to be set several times to natural objects in taking on the bearings from meridian to meridian; but they may be taken as showing a general agreement throughout the survey as to bearing, for the apparent discrepancies are very nearly such as are accounted for by the convergence of the meridians to the Pole. The difference between the meridians of the Bluff and Mount York, obtained in a similar manner to the other differences, is 29', to be added to the meridian of the Bluff. In plotting the survey, the latitudes of the prime stations were found to close the one with the other, as also with the latitude of Mount Hamilton, as determined by the Reconnaissance Survey of Southland. A discrepancy of rather more than 1' of longitude,