VALUE OP AUSTRALIAN LONGITUDES. 
191 
The longitude of Aden, reduced to Captain Heaviside’s longitude 
station, may now be derived bv combining the several values shown 
in the foregoing, in the manner adopted by Dr. Gill — (7) pp. 60-62 — 
omitting the value given for Alexandria-Mokattam, viz. : — ■ 
By the British Transit of Venus Expedition By Lord Lindsay's Expedition of 1874 
of 1874, and the Officers of the G, T.S. and Dr. Low. 
of India. 
h. m. sec. sec. h. m. sec. sec. 
(a) 2 05 06-240 ± 0'098 I 1 59 33'846±0'078 
(k) 0 05 06-931 ± 0-103 | {(^) + GO} 0 10 39-000 ±0 082 
(*„) 0 49 42-662 ± 0-060 j {(&) + (£-,)} 0 49 43-742±0'120 
(1) ... - 0 00 00-877 ±0 
A 2 59 55-833 ± 0154 
B 2 59 55-711 ±0165 
h. m. sec. sec. 
A 2 59 55' 883 ±0154 
B 2 59 55-711 ±0165 
Longitude of Aden (Captain Heaviside’s station) 2 59 55'776 ± 0113 
Dr. Gill considered the mean errors of the two values A and B as 
equal, and adopted for the definitive longitude of Aden f (A + B) 
(7) p. 62, viz. : — 
h. m. sec. Probable error. sec. 
Aden E. of Greenwich 2 59 55772 ± 0*079 (should be 0*076?) 
(m) Aden- Bombay . — Observer: Dr. Gill at Aden (Gill’s station). 
The operations at Bombay were conducted under the direction of 
Mr. C. Chambers, Superintendent of the Colaba Observatory. Time 
at Bombay was determined by a transit instrument 5 feet focal 
length. Records made by chronograph. Time signals sent by hand, 
and observed by eye and ear at both stations. These operations took 
place in 1875, on 31st January, concurrently with the determination 
Suez-Adeu by Drs, Gill and Low; the time observations of this single 
night being all that could be secured at Aden. The personal equation 
between the observers not determined — (9) pages 182-195. 
0»x) Aden-Bombay. — Observers: Captain Campbell at Aden, and 
Captain Heaviside at Bombay. This measurement was made with 
the same instruments and methods described in (& It ). The station at 
Aden was the same as that occupied by Captain Heaviside in deter- 
mining the interval (* n ). That at Bombay was 0*134 sec. east of the 
Colaba Observatory transit instrument. The operations were repeated 
on nine nights in 1877— April 30, May 1, 2, 3, 4, 5, 7, 8, and 9— 
giving accordant results. 
The two values (m) and (m t ) are quite independent. The former 
is based on observations and conditions not altogether satisfactory (as 
we have seen), with very limited time and great disadvantages, and 
involving the unknown element of the personal equation of the 
observers. The latter value (m t ) is the result of elaborate operations 
extending over a period of nine nights, and made under the best 
possible conditions ; yet these two results differ only by 0 03 sec. 
(ji) Bombay . — Difference of longitude between Captain Heavi- 
side’s station and the transit instrument of the Colaba Observatory. 
This was determined by a traverse measured under the direction of 
Captain Heaviside (11). 
