PEOCEE DINGS OE SECTIONS. 
Section A. 
ASTRONOMY, MATHEMATICS, AND 
PHYSICS. 
l.—ON THE MOST PROBABLE VALUE AND ERROR OF AUSTRALIAN 
LONGITUDES, INCLUDING- THAT OF THE BOUNDARY LINES OF 
SOUTH AUSTRALIA WITH VICTORIA AND NEW SOUTH WALES. 
Bit PIETRO BARACCHL , F.R.A.8. 
Since the issue of the Report on Australian Longitudes, in 1885, 
further information has become available through the publication of 
various works, especially Vol. I, of the Annals of the Cape Obser- 
vatory, and Yol. III. of the Dunecht Observatory Publications, relating 
to certain longitude determinations, upon which the Australian results 
partly depend.* 
It was not expected that on this account the adopted values would 
have suffered any material modification ; and even if such were found 
to be the case, the new values could hardly have been taken as final, 
knowing that several links in the long chain of connection between the 
prime meridian and Australia are regarded as weak, or at least capable 
of being strengthened. 
On the other hand, opportunities for making fresh measurements 
along this chain seem remote, and we may probably have to be satisfied 
with what we have for some years to come. 
This latter consideration induced me to examine the whole of the 
existing materials bearing on the subject, in order to form the most 
probable values of these longitudes, which may claim as their basis 
the full amount of evidence made known to the present dale. 
Since the telegraphic method was first introduced by the coast 
survey of the United States, its superiority to the older ones depen- 
dent on the motions of the moon, transportation of chronometers, 
&c., has been generally admitted. It is remarked by Professor Asaph 
Hall : (1) u The real probable error of a longitude found by means 
of moon culminations uuder the best conditions — that is, when the 
moon is compared with stars at both stations — amounts to two or three 
seconds of time.” 
Again, it has been shown by Dr. Gould (2) that the longitude of 
Washington, determined by transportation of chronometers across the 
Atlantic, and also by observations of moon culminations, oceultations, 
and eclipses, which gave apparently consistent results, was found to he 
more than four seconds of time in error when compared with the 
telegraphic determination of 1867. 
Note. — For list of works consulted, see Appendix II. 
