232 PROCEEDINGS OF SECTION A. 
their purpose satisfactorily, and possessing the merit of economy, 
were not connected in such a manner as to allow of exact com- 
parison of their respective base lines. 
The instruments used on these surveys were 7-inch theodolites, 
three rounds or sets of instrumental bearings were required to be 
taken with the vernier set at 360°, 120°, and 240° respectively. 
The length of the sides of the triangles ranged from 10 to 40 
miles, and the closing error in some cases was as high as 15”. 
Shortly after Mr. G. W. Goyder’s appointment as Surveyor- 
General, the triangulation of the Eastern Plains and Gawler 
Ranges was completed. 
In 1873 by the exertions of Mr. A. B. Cooper, Deputy 
Surveyor-General, the survey of the outlying districts was con- 
tinued upon strictly geodetic lines, the forms of record and methods 
of astronomical observations adopted being similar to those of the 
Victorian Geodetic Survey. This class of work has been continued 
uninterruptedly for twenty years covering about 1,000 miles of 
country. Seven-inch theodolites have been chiefly used since 1873, 
but good work giving errors of only one or two seconds per triangle 
has been done with a smaller German theodolite by “ Ertel,” 
having four verniers and an excellent telescope. 
The latest base line was measured during 1880 on a level 
flat 500 miles north of Adelaide. It was measured eight times 
with deal bars, 10 links in length, brass capped, and twice with a 
steel bar of the same length, all standard according to the brass 
yard previously referred to. Numerous stout stakes were driven 
into the ground in perfect alignment and to the same level; a 
copper tack was inserted into every stake, and upon these the bars 
were rested, and a fine line drawn at the end of each. Two sets 
of measurements were made in summer and two in winter, 
corrections for temperature being carefully applied. But the 
wooden bars were found to shrink more than ;}, of an inch, 
involving continual uncertainty. The length given by the steel 
red alone, viz., 9,107:71 feet was, therefore, adopted. While the 
line was in process of measurement, angles were taken at 
appropriate distances to stations on neighbouring hills which 
afforded facilities for extending the line. 
Astronomical latitudes have been determined by meridian 
passage of stars with both transit theodolite and sextant, which 
differ from the calculated positions by from 2 to 16 seconds. 
Some of these discrepancies are doubtless owing to deflection of 
the plumb line, as the altitude of the country varies from a few 
hundred to over 4,000 feet above sea level, but no systematic 
effort has been made to determine the extent of disturbance due 
to this cause. The observations for azimuth are taken at every 
second or third station, either with a 7-inch “Y” or a smaller 
transit theodolite ; a set consists of six or eight observations of 
