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Title
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Scientific. Science Notes.
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Description
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Australasian (Melbourne, Vic. : 1864 - 1946), Saturday 16 December 1899, page 25
SCIENTIFIC.
SCIENCE NOTES.
By PHYSICUS.
THE DRAKENSBERGEN.
About the middle of last year Mr. F. G. Churchill read a paper before the South African Philosophical Society, which gives us a clear idea of the physical structure of the rugged mountains forming the border line-between Natal and the Free State. The parts he visited are likely to have more than a passing interest to us. The scenery he describes as being very beautiful. Leaving the railway at Ennersdale, he passed through undulating country, dotted here and there with flat-topped hills. The rocks are like those round Dundee and Newcastle, namely, light-coloured sandstone and shales, and belong to the Upper Karoo series, which is about the age of the Sydney sandstone. Twenty miles further on he name on the Drakensbergs. The flat-topped hills are capped by what we call bluestone in Victoria, in other words a form of lava. We could, then, match the flat-topped hills on a small scale in Victoria between Dayles ford and Castlemaine, among what are known as the Loddon Outliers. The rock beneath the African lava is, however, in nearly horizontal beds, and it is among such horizontal beds, especially when capped by a hard rock-like lava, that we get a canyon like structure, developed by the ceaseless cutting action of the streams. Again, we can find a well-known Australian parallel, for the Blue Mountains of New South Wales, give us a clear idea of what we should find—precipitous cliffs, rising tier above tier, looking, as Mr. Churchill says, like a succession of camel-backs. In the canyons of the Tugela and Little Tugela, close to the main wall of the Berg, the depth is in some places as much as 2,000ft., and the vertical face of the lava cap 400ft. The area over which the author traced the
lava war some 60 miles by 15. The under lying sandstone is a compact, hard, gritty rock, of a cream or white colour, and. it weathers away in huge masses, leaving ver tical walls, or overhanging ledges. This upper Beries of sandstones is from 200ft. to 500ft. thick, and spreads over a large exr tent of country to the north and south, its top being about 3,000ft. above sea. level, rbe whole series of sandstones and softer beds is about 1,000ft. thick, and' its lower
part is full of caves.
^ Pushing further into the mountains, Mr. Churchill found the volcanic cover to thicken, till at Bushmab's Pass he esti mates the lava sheet to be 2,500ft. thick. \V hen the summit was reached there was a disappointment, from a scenic point of view—a dreary, forsaken wilderness of. rocky hills and desolate valleys, gently sloping into Basutoland. The mountains then, like the Blue Mountains of New South Wales, are mountains of denudation, and are not, from a scientific point of view, a mountain chain at all, but a gently-slop ing plateau, carved, it is true, into terrible gorges and cliffs, and presenting a rugged and broken escarpment facing Natal. The , summit of the plateau is desolate and un inhabited, and extends as a broad strip about 200 miles long from north to south. 1 There seem to be no volcanoes whence the
lava came, and, perhaps, it all welled forth from vast rents in the ground.
At one place, Champagne Castle, the Drakensbergs are 7,000ft. above the valley immediately below, and the canyon below the Tugela Falls surpasses anything Mr. Churchill ever saw in Europe. In places, he says, the gorge is not more than 40ft. wide, and in four miles the river-bed rises 1,200ft. The Tugela Falls themselves, with three steps, are 2,050ft. high. The climate in winter time is very cold, and snow fre quently falls, even during midsummer. If the Boers betake themselves to fastnesses like these the work of rooting them out will be no child's play.
EARTHQUAKES.
Among the reports read and discussed at the recent meeting of the British Associa tion was an interesting one on the present state of earthquake observation. It is stated that 23 stations at home and abroad are furnished with complete earthquake ob serving apparatus, or seismometers as they are called. The most important station in the British Isles is Prof. Milne's station, in the Isle of Wight. This station recorded 103 earthquakes last year; that is to say, vibrations of the earth which are suffi ciently powerful to be distinctly recorded by the instruments, though they may not have been felt without. The extent of ter ritory over which these disturbances were felt may be judged from the fact that 60 per cent, of them were recorded at various places in Germany, Austria, and Russia; while nearly as great a number of them were observed at Victoria, British Colum
bia.
An earthquake, it must be remembered, consists of a series of vibrations of the solid
earth. Bet" up by some meaw a&mt witfbfa we do not in general know very much at present. Even a landslip on a mountain will cause a small local earthquake, but the ordinary earthquake is due to disturb ances on a much greater scale at some dis tance below thesurfaeeof the e&nth. From this foaus, which is probably, miles across, the disturbance is propagated through the earth by wave motion of each of the two principal kinds; that is. to say, partly as longitudinal: waves, like those to wbich we awe the phenomena of sound in. the air; in which each particle moves backwards and forwaras in the line in which the wave progresses, and partly as transverse waves, inie those on the sea, where each particle
moves at right angles to the direction of
motion of. tha wave.
When an earthquake is felt the seismome ters generally show first a number of slight tremors lasting for a few seconds, then tue main shock, consisting of a few oscillations only, and then a number of small vibra tions, gradually dying away again.
The preliminary tremors are supposed to be due. to the longitudinal or compression waves, which necessarily travel faster than the transverse waves. The large 6hock is due to transverse waves which travel along the surface of the earth, and so resemble ordinary sea waves very closely.
By comparing the times at which an earthquake is observed at different places the position of the centre may be roughly determined, or at least of the point on trie surface of the earth vertically above the centre of the shock, the depth of the cenfre is considerably hard to determine.
It is curious to note that the violence of a shock is often less at points nearer the centre than at others further off; thus some earthquakes that originate in Japan give a smaller effect at Victoria (B.C.) than at the Isle of Wight, though tliey have travelled twice aB far to reach the latter place, the water seeminv to have au effect, in general to diminish the strength of the
shock.
Each earthquake seems to have a charac ter of its own, which impresses itself on the record made by the instruments. Gn ac count of this peculiar character it has been possible for Mr. Milne to correctly predict, from examination of his own seismographs, that an earthquake report telegraphed from Japan gave the wrong date by 24 hours.
THE CONSTITUTION OF THE ATMOSPHERE, <
We have explained before the reasons given for the absence of hydrogen and helium from the atmosphere of the earth, and the total absence of atmosphere from tlie moon. The general explanation adopted is that a substance like hydrogen,
consisting of very light molecules, has these , molecules moving with a very high rate ot speed, according to the kinetic theory of
gases, and occasionally some of the mole- j cules are moving in such a direction, and high up in the atmosphere, that they can actually escape from the influence of the earth's attraction altogether.
At the British Association, Mr. Bryan gave some more calculations on this sub ject. He shows that if the earth possessed hydrogen in its atmosphere now, it would he so seldom that molecules would escape the earth's attraction that such an atmos phere would be practically permanent. But a rise of temperature greatly increases the possibility of escape. Thus, at a tempera
tiira'a - -t, take 600,000 years for as much hydrogen to" escape as would form a layer one^ centi meter thick all over the earth, wlule 'the f same amount would escape in 220 yeara it { the temperature was constantly about 80 'Fahrenheit. It follows that if we are
to continue to accept this explanation^ as, however, seems reasonable, we must sup* pose tiie. hydrogen and helium to have dis ; appeared at a time when the earth was in
| w highly heated condition. The disappear
ance of the amount mentioned above would he quite inappreciable to a barometer.
IRISH GOLD.
Though Irish diamonds are not what their name might lead us to believe, namely, true diamonds, but only quartz crystals, yet, as is well known, it is quite otherwise ■with Irish gold, for the existence of. gold in the Wicklow Mountains has long: been known. Gold ornaments of prehistoric: age are still occasionally found in the ancient burial-places, and, though some of" the metal of which they were composed may have been traded from far, yet there is reason to believe that part, at any rate, of the gold was of local origin. In later times, about the year 1795, several families of peasants found the value of the deposits and gold, washing took place in a secret manner. Then the news leaked out, and a rush took place, and in six weeks about 80Goz., with a value of some £3,060, was obtained by the peasantry. The Govern ment then stepped in and took possession. In a recent paper, Mr. V. Ball describes the steps he ha- taken to clear up the his tory of some of the nuggets which were found-about that time. The heaviest re corded is one of about 40oz., but this is shown to be due to a misprint, for the true weight was only some 4oz.
One of the specimens in the collection of the Science and Art Museum is a cast of a nugget said to have weighed about 22oz., and round the original specimen a rich crop of myths has sprung up. One story says that the original nugget was presented to George IV. on the occasion "of his visit to Ireland in 1821, at the instigation of an "officious member of the Dublin Society. Another variant sayE that King George, on seeing the nugget, promptly pocketed it as his own property, which by law it was. There does not seem to have been any foundation for either of these stories, and. the idea of the King so far forgetting him self as to load his pocket with the weight of a 22oz. nugget is rather far-fetched, and,
in fact, a claimant to the fabrication of the story has been unearthed. At the time of the King's visit, a 3oz. nugget was in the collection, and it is there now. The 22oz. specimen seems to have been discovered by eight peasants in 1795, and to have found its way into the hands of the King, having been presented by Abraham Coates, who was rewarded with a Government post, was a J.P., and has a street in Wicklow named after him. Tradition says that George III., who was the recipient, caused the gold to be made into a snuff-box, and Mr. Ball hopes that inquiries at Windsor Castle, hitherto of a negative character, may yet result in finding out what became of the gold. A fair number of mights, ranging from 5oz. down, have been re corded, and several are in various mue<r uins, but the Wicklow gold mines have nofc proved very productive, the matrix has not been found, and the country needs "loaming."
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Date Issued
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1899-12-16
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Creator
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Physicus
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Publisher
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The Australasian
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Links to Trove
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https://trove.nla.gov.au/newspaper/article/138612341
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Location State Territory
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Victoria
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Location Town City
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Melbourne
