VALUE OF AUSTRALIAN LONGITUDES. 
199 
h. m. sec. 
Longitudeof Sydney by culminations, with weight 2 10 4 49-10 
„ „ occupations, with weight ! 10 4 50*32 
„ „ absolute methods ... 10 4 49*93 
Longitude of Melbourne, by absolute methods ... 9 39 54*53 
Taking the four values — (i.),(ii.), (iii.),aud (iiii.) — and combining 
them with the weights assigned bv Dr. Auwers, the mean error of the 
result is found to be 0*581 sec. Wo have then — 
h. m. sec. 
Longitude of Sydney by absolute methods ... 10 4 49*93 ±0*581 
Longitudeof Sydney by telegraphic method (xii.) 10 4 49*39+0*182 
which, being again combined with weights derived from their mean 
errors, give us definite longitudes based on all evidence available— 
h. m. sec. 
Sydney 10 4 49*44 (xiii.) 
Melbourne 9 39 54*04 (xiv.) 
The theoretical errors would show* that the amount of uncertainty 
of the two methods is about as 1 : 3, a result not inconsistent with the 
estimation that might otherwise be made of their respective degree of 
accuracy, judging from the nature of the eases and the circumstances 
surrounding them, and not disparaging to those able astronomers who, 
by long and patient observations of the moon, gave to Australian 
longitudes values so closely accordant to those obtained by the easier 
and simpler system of galvanic signals. 
EASTERN BOUNDARY OF SOUTH AUSTRALIA. 
Boundary Line between South Australia and Victoria . — As the 
business of this paper is limited to assigning the most probable value 
and error to the longitude of the line actually marked on the ground, 
and proclaimed in the South Australian Gazette of 23rd December, 1847, 
to be the common boundary of tho two colonies of South Australia 
and Victoria, it will not be necessary here to recapitulate the history 
relating to the determination of its geographical position. Suffice it 
to say that, in 1839, Mr. C. J. Tyers assigned a certain longitude to a 
point on the eastern entrance of the liiver Glenelg, based upon the 
longitude of the Parramatta Observatory (the only known longitude 
at the time), and determined differentially by transportation of 
chronometers to Melbourne, and by triangulation from Melbourne to 
the Glenelg, checking his work by lunar observations made with a 
sextant at Portland Bay; that in 1846 Mr. Surveyor Wade deduced 
from i yers’ determination what would be the position of the 111st 
meridian of east longitude from Greenwich, and actually marked 
this meridian on the ground, from the sea shore in latitude 38° 4' 3 7 to 
latitude 36°, and that the marking of the same line was continued 
northward to the Diver Murray, in 1849-50, &c.— (17). 
r l wo points near the southern end of this line — viz., Pile No. 3 
and Pile No. 4— were connected by Mr. A. C. Allan with the Trigono- 
metrical Station at Mount Buskin, whose geodetic longitude is deduced 
