TRANSIT OF MERCURY. 
209 
Mr. Stanley; and No. 4230, siderial, by Kullberg, under the care of 
Mr. Cleminson. The first belongs to Mr. Stanley’s observatory ; but 
the others, one of which is the property of the Hon. A. C. Gregory, 
were duly compared with the standard clock at the Brisbane city 
observatory for several days previous, and late on Saturday night, 
immediately before Mr. Cleminson and I transported them to Too- 
wong, the former gentleman finally checked them by meridian stars. 
After the transit had been observed the chronometers were at once 
returned to the city observatory and re-compared. No. 4230 was 
found to have uudergone no change whatever in transit, but there was 
a very slight displacement observed in the rate of the mean time 
chronometer. This recalls to my mind a similar experience at the 
time I was preparing to observe the Transit of Venus at Levuka, Fiji, 
in 1882. On that occasion three chronometers were also rated, 
although only one, the best, was actually used to record the times of 
the observations. Some two weeks before the date of the transit 
they were transported with the greatest possible care for a very short 
distance from the harbour master’s office to the observatory, when it 
was found that a very slight change of rate had taken place.* 
Weather . — Shortly after 5 o’clock the sun rose above a clear 
horizon, free from the slightest trace of haze. The whole sky was 
cloudless, the weather nearly a dead calm, and the atmosphere almost 
phenomenally .steady and agreeably warm. A few preceding days of 
line clear dry weather had happily dissipated the moisture accumulated 
in the atmosphere during previous daily showers, and thus we were 
privileged to conduct the observations under the most favourable 
conditions, in every respect typical. After considerable experience in 
astronomical work, I can honestly state that in no climate have I ever 
conducted astronomical observations under more favourable atmo- 
spheric conditions than those prevailing at Brisbane on the morning 
of 1894, November 11. A fair idea of these may be conveyed by 
stating that from sunrise till shortly before the internal contact the 
planet appeared against the solar surface as a clear and sharply 
defined disc through a small portable telescope which Mr. Stanley had 
placed outside the observatory door; and Mr. C. B. Lethem, observing 
with a 5-inch theodolite at Clayfield, some six miles north-east of our 
position, was able to record the interval of time between internal and 
external contacts, by an ordinary watch, to within seventeen seconds of 
the calculated interval. 1 bavo purposely emphasised this description 
of the weather, having long ago arrived at the conclusion that the 
so-called black drop and other somewhat remarkable phenomena 
associated with the observations of the transits of planets are 
terrestrial causes and not celestial. In other words, they arise from 
unfavourable atmospheric conditions, from telescopic defect, and 
from some peculiarity in the physical condition of observers — either 
one or all combined. This subject has, I may state, been very ably 
elucidated by the distinguished astronomer, Mr. II. C. Russell, in a 
valuable paper upon a previous Transit of Mercury contributed to the 
Royal Society of New South Wales, 7th December, 1881. My own 
experience entirely confirms the views advanced by Mr. Russell. 
* Proceedings and Transactions of the Royal Geographical Society of Australasia, 
Queensland, vol. vii., p. 93. 
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