of Van Dieme77^s Land. 89 



the accuracy of the angular observations, the^rror rarely 

 amounting to more than four or five seconds, and generally 

 not exceeding two seconds. The observations have been all 

 made by Mr. Sprent, and with the same twelve-inch instru- 

 ment. 



By means of the repeating table each angle is observed 

 under a series of repetitions, and the mean obtained is ex- 

 ceedingly near the truth. 



At every principal station Angles of Elevation and De- 

 pression for determining relative altitudes have been observed, 

 and at several stations astronomical observations made for 

 the determination of the true meridian. 



The observations taken for this purpose are extreme 

 Elongations of circumpolar stars ; — both the east and west 

 elongation of one or more stars, with single elongations east 

 or west of others ; — observing their azimuthal angle from 

 another station, or from a fixed lamp whose position with 

 reference to some other station is known. 



The observations have been made with the principal instru- 

 ment at sixty-eight main stations, and with an eight-inch 

 theodolite at sixty-five secondary stations, those at the latter 

 being confined to the horizontal angles. Mr. Sprent is con- 

 tinuing the observations for the main tri angulation, during 

 the summer, in the north-west portion of the island, and pre- 

 parations are made for those in the south-west next summer. 

 In the meantime, I am in the expectation of being able 

 shortly to appoint two other parties for carrying on the se- 

 condary and minor triangulation ; but the extreme and urgent 

 demand at present for surveys of small blocks of land, and 

 the want of strength in the establishment, delays this work. 



Besides the calculations connected with the two Base lines, 

 and the four series of triangles between them, to which I 

 have already adverted, about three hundred triangles have 



M 



