VALUE OF AUSTRALIAN LONGITUDES. 
197 
(# x ) Port Darwin to Melbourne.— Observers: Mr. E. J. White at 
Melbourne, and myself at Port Darwin. The operations were exactly 
similar to those described in the two preceding intervals. Time 
signals were exchanged on four nights — viz., February 15, 23, 26, 
and March 2(1883), the individual results being very fairly accordant. 
The personal equation between the observers was determined before 
and after the expedition — (6) page 22. 
The value (#,) ought to be equivalent to the sum of (#) and (y). 
We have, in fact — 
h. m. sec. 
sec. 
Adelaide to Port Darwin (x) ... ... 0 30 57*80 ± 0*041 
Melbourne to Adelaide ( y ) ... ... 0 25 33*84 ± 0*050 
Melbourne to Port Darwin, indirect ... 0 56 31*64 
Melbourne to Port Darwin (pc$ direct... 0 56 31*66 ± 0*044 
(z) Sydney- Melbourne . — This interval was measured five times by 
direct connection of the observatories between the years 1861 and 
1884. The operations consisted, as usual, in the automatic exchange 
of clock-beats, producing chronographic records at the two observa- 
tories, and in time determinations made with the transit circles of 
these institutions, the whole under the direction of the respective 
Government astronomers. An indirect determination was made in 
1868 through the longitude station at the western boundary of 
Victoria, of which more hereafter. 
The last indirect measurement took place in 1887 through 
Mr. John Tcbbutt, private observatory at Windsor, New South Wales. 
Mr. Tebbutt made bis time determinations with a small transit 
instrument: sent his signals by hand from the local telegraph office, 
which is at a distance of (?) miles from his observatory, using a mean 
time chronometer, and observing the incoming signals by coincidence 
of beat. Ills operations were conducted with great care, and gave 
very satisfactory results. 
The astronomers at Melbourne give great weight to the value of 
1861, and to those of May and August, 1884. The mean of the five 
independent values is 24 min. 55*408 sec. The mean of the last two 
is 24 min. 55*395 sec., and that of 1861 is 24. min. 55*38 sec. The 
value 24 min. 55*40 sec. was adopted in (6) page 24 as the most 
probable. W e may now conclude the longitudes of the three principal 
observatories east of Greenwich on the evidence of the telegraphic 
method alone, as follows, viz. : — 
Longitude of Port Darwin, IX. 
Port Darwin to Adelaide Observatory (x) 
Longitude of Adelaide Observatory, X. 
Melbourne- Adelaide (y) 
Longitude of Melbourne Observatory ... 
Longitude of Port Darwin, IX. 
Melbourne to Port Darwin (x,) 
Longitude of Melbourne Observatory, XI. 
Sydney-Melbourne (z) 
Longitude of Sydney Observatory, XII. 
h. 
8 
0 
9 
0 
9 
8 
0 
9 
0 
10 
43 22*34 ±0152 
30 57*80 ± 0-041 
14 20*14 ± 0*157 
25 33*84 ± 0*050 
39 53*98 ± 0*165 
43 22*34 ±0*152 
56 31*65 ± 0*044 
39 53*99 ± 0*158 
24 55*40 ± 0*091 
04 49*39 ± 0*182 
m. sec. sec. 
