VALUE OF AUSTRALIAN LONGITUDES. 
189 
The following values were adopted, viz. : — 
(9) page 49 L — h. m. sec. 
By Dr. Copeland ... 1*59*33*807 
(7) page 60 — 
By Dr. Auwers 1*59*33*885 
(8) page 330 — 
By British Transit of Venus Expedition ... 1*59*33*69+0*156 II. 
The values I. and IT. of the longitude of Alexandria are indepen- 
dent. Their difference is 0*156 seconds. 
(g) Alexandria- Suez . — Observers : Dr. Low at Suez, Dr. Gill 
at Alexandria. Instruments for time determination, same as already 
stated above. Galvanic signals exchanged on five nights — viz., 1875, 
February 19, 20, 23, 24, and 25. Signals sent by hand; observations 
made by eye and ear. At both stations the chronometers had to be 
carried for some distance to exchange signals. Result computed by 
Dr. Copeland — (9) page 492. 
(g,) Alexamlria-Sucz. — Same operations as in (y). Result 
deduced by Dr. Auwers — (7) page 60. 
{h) Mokatfam-Suez . — Observers : Mr. Hunter at Suez, Captain 
Brown at Mokattam. The instruments used by these observers have 
already been referred to in (a) and ( b ). The signals were sent by 
hand, and the observations made by eye and ear. Operations repeated 
on four nights — viz., 1874, December 4, 5, 7, and 14. The station 
used by Mr. Hunter was not the same as Dr. Low’s station. The 
former appears to have given trouble on account of its instability. It is 
remarked by Mr. Hunter — (8) page 333 — “The only defect arose from 
the looseness of the soil, causing the level readings to vary a good 
deal.” The samo complaint is also made by the officers of the Great 
Trigonometrical Survey of India, who used this station in 1877 — viz., 
that their observations may be somewhat vitiated "by the unsteadiness 
of their instruments, due to looseness of the soil — (12) page 4 5a. 
(i) Difference of longitude between Dr. Low’s and Mr. Hunter’s 
stations at Suez. 
This was determined by Dr. Gill bv time observations made by 
himself with Dr. Low’s transit instrument mounted at one station, 
and with his altazimuth mounted at the other station, and by trans- 
portation of nine chronometers to and fro. The value thus found 
was 0 32 seconds— (9) page 262-266. 
(&',) The same interval as (i), determined bv a traverse under 
the direction of Captain (now Colonel) Campbell, R.E. ; its value was 
found to be 0*025 seconds — (9) page 491 and (11) Appendix to Part 
II., page 109. The discordance between the two above values is 
0*295 seconds. This may be probably accounted for, or at least 
partly, by the length and complex character of Dr. Gill’s operations, 
when compared with a simple traverse; and also by the circumstance 
remarked in (9) page 262, that “these operations required seven and 
a-half hours of continuous observing, involving great fatigue.” 
We have thus the two following independent values for the 
interval Alexandria- Suez, reduced to Hunter’s station, by adopting 
value (i\), viz : — h. m. sec. 
i {(</) + (/)} + f, ... 0 10 39*025 + 0*082 
(b) + (h) 0 10 39*481 + 0*160 
which differ by 0*456 sec. 
Mean error. 
mean 1*59*33*846 + 0*078 I. 
