TRIGONOMETRICAL SURVEY OF NEW SOUTH WALES. 209 
MINOR TRIANGULATIONS. 
Before proceeding to the astronomical work of the survey it 
may be mentioned that to meet various needs, independent 
triangulations have been made at Sydney, Albury, and Newcastle, 
which have afterwards been connected with the main triangulation. 
These were founded upon bases measured with steel tapes, and 
the comparisons of the lengths, made on connection, shows the 
reliance which may be placed upon such tape measurements when 
conducted with only ordinary care. Elsewhere in this paper 
the main triangulation only is treated of ; the large amount of 
minor work done may be estimated from the accompanying map 
(marked “C”) which illustrates the detail triangulation of one of 
the counties on the south coast. The whole extent of the survey 
is shown roughly on map marked “ D,” the part covered by the 
primary triangulation being distinguished by cross-hatching. 
ASTRONOMICAL OBSERVATIONS. 
During the progress of the survey, astronomical observations 
of the latitudes and longitudes of a number of stations have been 
made, and the azimuth of the work has also been referred to the 
astronomical azimuth at a number of places. The stations at 
which these determinations have been made are distinguished by 
special symbols on map “A.” At each station visited the 
horizontal direction of the magnetic needle is observed, but no 
measures are made of dip or intensity, the other two elements 
requisite in investigations of the earth’s magnetic force. 
LONGITUDE OBSERVATIONS. 
The adopted longitude of the initial point of the survey, the 
Sydney Observatory, is 10h. 4m. 49°54s. east. This is the value 
deduced from the connection between Australia and Asia effected 
by Mr. Barrachi and Captain Darwin in 1883 when the difference 
of longitude, Port Darwin to Singapore, was observed and the 
connection of Port Darwin with Sydney was made. Since the 
adoption of this value, other determinations of the longitude arcs 
on the chain between Singapore and Greenwich have been made, 
notably that recently completed by Captains Burrard and Lennox- 
Conyngham, which gives a value for the longitude of Madras 
differing by —0-308s. (4:62”) from the value, 5h. 20m. 59:42s., 
used for fixing the Australian longitudes. New measures of this 
kind, of course, affect the Sydney longitude, and must be taken 
into account whenever a re-discussion of the subject takes place, 
but any alteration at present, to accord with these later determina- 
tions, is to be deprecated ; in fact, considering the many and 
remote causes of error in longitude observations over long lines, it 
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