Dec. 21, 1882] 
NATURE 
al77 
at none of the lower stations gave indications of the 
ascensional and descensional movements of the atmo- 
sphere to which attention is here directed. 
We observe from a circular we have before us, signed 
by the Duke of Richmond and Gordon, President of the 
Scottish Meteorological Society, that the Society has 
obtained from Mrs. Cameron Campbell of Monzie, a 
suitable site for the proposed observatory on the top of 
Ben Nevis, that the grounds and buildings are to be 
invested in the Royal Society of Edinburgh, and that the 
charge and management of the observatory will be in the 
Council of the Scottish Meteorological Society, in con- 
junction with two representatives of the Royal Society of 
Edinburgh, and one representative of the Royal Society 
of London, the represeutatives of the former Society 
being Prof. Tait and Prof. Chrystal, and that of the 
latter Sir William Thomson. 
It is satisfactory to learn that a good beginning has 
been made towards raising the 5000/. required to esta- 
blish the observatory, by a number of noblemen and 
gentlemen, who have intimated handsome subscriptions 
to the fund. Since, however, a large sum remains yet to 
be subscribed, we earnestly hope that in the interests of 
science the remaining balance of the 5o000/. will soon be 
subscribed, so that next summer may see the Ben Nevis 
Observatory an accomplished fact. 
NOTES ON THE GEOLOGY OF HONGKONG 
RITING in 1843, Dr. Abel determined the main 
structure of the island to be of basaltic trap, 
granite, siliceous and schistose rock. Mr. Kingsmill in 
1865, in his excellent papers on the Geology of the 
Kwangtung Province, was the first to notice the trachytic 
porphyry of Victoria Peak (1823), the summit of which 
overlooks the town. This trachytic rock has been appa- 
rently forced upwards through the granite after the over- 
flowing and partial hardening of the trapon the west side 
of the island. It was Mr. Kingsmill also who explained 
the nature and formation of the pseudo-boulders, with 
which the island is so plentifully covered. Towards the 
extreme south-east, near Cape d’ Aguilar, these pseudo- 
boulders assume very large dimensions, and their weather- 
beaten aspect proves that the chemical action of water 
and plants, which forced them from the parent rock, 
occurred a long time ago. Indeed the island must have 
undergone great changes in course of time: the hill 
beyond Shekko, for instance, must have been originally 
nearly or quite as high as Victoria Peak, whereas its 
present elevation is not more than 500 feet. The rapid 
action of the heavy rains and rich vegetation is nowhere 
more apparent than in the high hill (directly back of the 
peak from which the colony takes its name) known as the 
Hog’s Back, or High West. Its eastern slope is literally 
covered with pseudo-boulders, rendering the ascent from 
that side not a little dangerous, and in the rainy season 
large masses of rock are borne down into the valley 
beneath. 
Now that the population of the isl.nd has increased, 
amateur geologists and mineralogists have become toler- 
"ably plentiful, and frequent excursions are made, hammer 
in hand, to the less known and wilder portions of the 
island. In this manner traces have been tound of not a 
few minerals and several interesting rocks. Silver has 
been observed in small quantities, also galena, lead, and 
iron pyrites ; slate near Aberdeen, syenite and dolorite 
on a cliff overlooking that one-time piratical rendezvous, 
Saiwan, feldspar and grey mica abundant. 
One of the most interesting finds is that of molybden- 
ite, near the village of Sau-ki-van. Molybdenite, molyb- 
denum glance MoS,, was not known hitherto to be among 
the mineral products of China. Germany, Sweden, and 
Cornwales are the chief localities for this rare mineral, 
and it has been found in several parts of the United 
ee SSS et 
States. The South China specimens show all the well- 
known characteristics of European molybdenite—colour, 
lead-grey, streak the same; thin foliated hexagonal 
plates, closely resembling graphite ; flexible, non-elastic 
lamine, H.=1-2, G. 4, 5. A local chemist corroborated 
the determination by analysis, and found the composition 
to be— 
Sulphur ... = 40°0 
Molybdenum = 60°0 
Molybdenum sulphide =100'0 
It will be seen from this analysis that there is a slight 
decrease in the quantity of sulphur, compared with Euro- 
pean molybdenite. Dana gives the composition of 
American molybdenum sulphide as follows :— 
Sulphur = 410 
Molybdenum ="59'9 
100°0 
The mineral was found in small lumps imbedded in 
the granite. F. WARRINGTON EASTLAKE 
Hongkong, November 
TRANSIT OF VENUS, 1882—B8RITISH 
EXPEDITIONS 
AS operation which requires for its success the collec 
tion of nearly simultaneous astronomical observa- 
tions over widely separated portions of the earth’s surface 
must always be liable to great risks of failure. These 
risks may be diminished bya careful selection of stations, 
and an increase in their number; but they can never be 
entirely removed. 
The telegrams already received show, however, that 
the British expeditions have been most fortunate; and 
the success of the work is now assured. 
This is not the proper place for a technical discussion 
of the different methods which may be adopted for the 
determination of the sun’s distance from a discussion of 
observations of Venus in transit; but it is desirable that 
some facts should be stated which may enable the reader 
to form some conception of the strength of the method 
which has been relied upon in the organisation of the 
British expeditions, and the probable accuracy of the 
sun’s distance which may be deducible from a careful 
discussion of the observations which have been collected. 
On December 6, 2h. 20m. G.M.T., the sun was distant 
from the earth about 90,620,000 miles, whilst at the same 
time Venus was distant only about 24,330,000 miles. 
The ratio of these two numbers is very accurately known, 
but the expression of either of these two distances in 
terms of any unit of length which is directly known to us, 
as a mile, is a point of great difficulty on account of the 
small dimensions of our earth, of which the diameter is 
only about 7912 miles, in comparison with such dis- 
tances as those of Venus and the sun. 
The greatest possible displacement of Venus, as seen 
projected on the sun’s disc from any two places on the 
earth’s surface is only about a twenty-ninth part of the 
solar diameter. It is from such displacements that the 
relation between the distances of Venus and the sun and 
the separation of the observers, which is known in miles, 
is established ; but the maximum displacement is never 
practically available. 
These displacements may be measured in many 
different ways: we can take photographs of the sun’s 
disc at the different stations, and afterwards measure 
from the photographs the distances between the centres 
of the planet and the sun, as seen at the different sta- 
tions; or the distances between the centres may be 
directly measured with a heliometer or any equivalent 
instrument ; or we may avoid the difficulties and errors 
