VALUE OF AUSTRALIAN LONGITUDES. 
201 
The interval Sydney-Melbourne, as previously mentioned, was 
also determined directly on 3rd April, 1868, bv exchange of galvanic 
signals between the observatories. The signals sent by Sydney to 
Melbourne were transits of fifteen stars (previously selected), observed 
in turn by Messrs. Smalley, Russell, and Todd, with the Sydney 
transit circle. 
These signals were automatically recorded on the chronograph at 
Melbourne, together with the times of transit of the same stars 
observed by Mr. White at meridian passage at the latter place. The 
signals sent by Melbourne to Sydney were simply clock-beats. 
The result of these operations, gave — (17) — 
Interval, Sydney-Melbourne (direct) Ohr. 24 min. 55*81 sec. (D x ) 
The values (C 1 ) and (D J ) differing only by O'llsec., the results 
from the operations of 1868 were readily accepted as entirely satis- 
factory. The adopted longitude of Sydney, from which Mr. Todd 
deduced the position of the 141st meridian, was — (17) — 
10 hr. 04 min. 48*97 sec. 
The boundary between South Australia and New South Wales 
was accordingly fixed at a distance of 2 miles 44 chains 684 links from 
Mr. Todd’s station, measured by him and Mr. A. B . Cooper, Deputy 
Surveyor- General of South Australia, along a line run due east from 
the centre of the Boundary Pier. It was also found that the marked 
boundary between South Australia and Victoria, when prolonged to 
the north of the Murray, intersected this easterly line at a distance of 
25 chains 68 links from the centre of the said pier — (17). 
I must now remark that the values (C 1 ) and (D 1 ) compare 
unfavourably with the other five direct determinations of the interval 
Sydney-Melbourne, being the largest of them all, and differing from 
their adopted mean — (6) page 24 — by 0*55 sec. and 0*4 L sec. respec- 
tively. 
This discordance of more than half a second of time will neces- 
sarily be felt in full in the deduction of the longitude of the Boundary 
Pier, and consequently of the actually marked boundary lines, as the 
most probable value of the interval Sydney-Melbourne, as far as 
can be known at present, and also the one already adopted — (6) 
page 24 — is — 
Ohr. 24 min. 55*40 sec. 
It is much to be regretted that the operations of 1868 were so 
very limited, considering the importance of the results expected from 
them. Value (D‘) rests, in fact, on the observations of a single 
night, made by four different observers, three of whom, as we have 
seen, observed transits with the Sydney transit circle in turn. It 
must also be noted — 1st. The signals exchanged were of a different 
nature, being sent by the observer in one direction, and by the clock 
in the other. 2nd. The constancy in personal equation may have been 
greatly disturbed by the unusual circumstances surrounding the 
observations at Sydney. 3rd. The signals at the boundary were sent 
in one direction only. This may probably involve a very small error 
only ; hut there is no direct proof that such error is negligible. It 
may, indeed, be considerable in the case of the interval Sydney- 
Boundary, with 900 miles of wire, indifferent circuit, and difficulty in 
adjusting the electric apparatus, causing the record of many signals 
