Page images
PDF
EPUB

may be supposed to arise in particles very slightly attached to the disk; this is radiated off chiefly during rotation, and probably does not greatly affect the disk afterwards.

(2) There is a surface gas-effect, which in an aluminium and even in an ebonite disk is conducted into the interior as it arises, so that it does not greatly radiate during rotation of the disk (art. 26). In a paper disk, however, which is formed of a badly conducting material loosely put together, part of the effect does escape as radiation during rotation (art. 27).

(3) There is a residual effect, which is more deeply seated than the gas-effect. And inasmuch as radiation takes place from a perceptible depth, this effect is much more influential than the gaseffect in increasing radiation after rotation. In the case of a paper disk, this deeply seated effect will be less diminished by radiation during rotation than the gas-effect, and therefore after rotation in such a disk we might expect the gas-effect to be peculiarly small (art. 35).

47. In the course of these experiments we have endeavoured to prove that this residual effect is not caused by vibration. The radiation-experiments with aluminium disks of three different thicknesses went, on the other hand, to show that it was of the nature of a surface-effect. This is confirmed by the results derived from tapping; for, in the first place, the experiments of art. 45 show that the two effects (the residual and the gas-effect) are probably distributed in the same proportion, going from the centre to the circumference of the disk. Again, taking the two disks of thickness 05 and 025 of an inch, we obtain the following results :

Thin disk

Effect for hyd.
48 (22 observations).

Thick disk.... . . 29 (20 observations).

[blocks in formation]

Now, allowing for errors of experiment, we see that the residual, as well as the gas-effect, is reduced to about one half for the thick disk.

Again, an experiment of a similar nature gave the effect for hyd. in an ebonite disk of in. in thickness =33, against a result =55 for the thin ebonite disk. Unfortunately it was omitted to make a comparison with these two disks for the gas-effect; nevertheless these results are all in favour of the residual effect being a surface-effect.

48. It might be well to make one remark regarding these experiments. They are not like the radiation-experiments, which required an extremely delicate instrument in order to give a sensible effect. But, on the other hand, the effect obtained by tapping being that due to the mere surface of the disk, is liable to be altered by any thing which affects the surface of the disk. We have come to the conclusion that in such experiments it is unadvisable to use a porous hygrometric surface, such as that of paper, not having its pores filled with paraffin or some other similar substance. It is likewise desirable that all parts of the apparatus should be as nearly as possible of the same temperature; indeed we suspect that some ex

periments made during some very peculiar summer weather were influenced by a want of temperature-equilibrium between the various parts of the apparatus, the result appearing to be that the gaseffect for the ebonite disk was abnormally large.

49. Our conclusion from the evidence before us is, that the residual effect is a surface-effect more deeply seated than the gas-effect, but distributed outwards from the centre to the circumference, very much in the same manner as the gas-effect. The residual effect likewise appears able to penetrate a chamois-leather blind without any perceptible diminution. We regard these conclusions as preliminary, and shall endeavour in our future experiments to procure additional evidence of these properties of the residual effect, as well as to obtain new facts regarding it. In the mean time, as the subject is one of interest, and has been already too long delayed, we have not hesitated to bring these results before the notice of the Royal Society.

In concluding we would desire to express our thanks to Mr. F. Kingdon for his assistance to us in many of these experiments. June 19.-William Spottiswoode, M.A., Treasurer and VicePresident, in the Chair.

The following communication was read :—

"The Diurnal Variations of the Wind and Barometric Pressure at Bombay." By F. Chambers.

The object of this paper is to bring to notice a remarkable relation that has been found to exist between the diurnal variations of the wind and the barometer at Bombay.

The observations made use of are the records of a Robinson's anemograph during the first three years of its performance, viz. from June 1867 to May 1870, and the corresponding hourly observations of the barometer and the dry- and wet-bulb thermometer made at the Government Observatory, Bombay.

The mean results for each hour of the day during the whole period and the mean diurnal variations of each element are tabulated and graphically represented by figures. The diurnal variation of the wind is then investigated, the most influential part of which is attributed to the land- and sea-breezes which blow from E.S.E. and W.N.W., and are shown to follow mainly the same law of progression as the temperature of the air, thus affording confirmatory evidence of the truth of Halley's theory of the trade-winds as applied to land- and sea-breezes.

Some peculiarities of the curve representing the land- and seabreezes are then pointed out, and these, the writer concludes, are due to the superposition of another distinct variation having two maxima and two minima in the twenty-four hours, like the barometer variation; and he supports his views by a reference to the variation of the east components of the wind in the months of July and August, when the land- and sea-breezes have almost disappeared. This is found to exhibit a decided double period. The north components of the land- and sea-breezes are then approximately eliminated from the north components of the whole variation, and the

variation which then remains exhibits a very decided double period in this direction also. These variations with double periods are regarded as indicative of the existence of a double diurnal variation. in the general movements of the atmosphere. Upon this hypothesis typical diurnal variations of the wind are deduced for north and south low latitudes-that for north latitudes exhibiting a double diurnal right-handed rotation, and that for south latitudes a double diurnal left-handed rotation; and from these the diurnal variation of the barometer is deduced.

The movements of the wind-vane at Bombay are then analyzed; and the writer concludes that the greater part of the excess of "direct" over "retrograde" rotation of the vane at Bombay is due to the diurnal variation of the wind.

Extracts are given from observations made at St. Helena, Toronto, and Falmouth, showing the character of the diurnal windvariations at those places, and their greater or less agreement with the deduced typical curves. The writer maintains that these variations afford independently a possible, if not a probable, explanation of that movement of the air which Dove had called the "Law of Gyration;" and, in conclusion, he points to the extent of their applicability in deducing weather probabilities, and to the method of discussing storms.

A postscript is added, giving the mean diurnal variation of the wind at Sandwick Manse, Orkney, and pointing out its general conformity with the results deduced from the Bombay wind-obser

vations.

GEOLOGICAL SOCIETY.

[Continued from p. 77.]

February 26, 1873.-Prof. Ramsay, F.R.S., Vice-President,
in the Chair.

The following communications were read :

:

1. "On the Jurassic Rocks of Skye and Raasay." By James Bryce, M.A., LL.D., F.G.S.

In this paper the author described numerous sections of Jurassic rocks exposed chiefly in the sea-cliffs of Skye and Raasay, indicating the presence in those islands of a complete series of beds ascending from the Lower Lias to the middle of the Middle Oolite. He noticed the occurrence in these sections of fossils belonging to the zones of Ammonites angulatus and A. Bucklandi in the Lower Lias, to the zones of A. Jamesoni, A. capricornus, A. margaritatus, and A. spinatus in the Middle Lias, of Upper Lias fossils, including Ammonites communis, falcifer, heterophyllus, and bifrons, and of others indicating beds belonging to the Inferior Oolite and Cornbrash and to the Oxford Clay. The Loch-Staffin beds were described as an estuarine series, nearly approaching the Oxford Clay in geological age, and including a bed almost entirely made up of the shells of Ostrea hebridica.

The whole series of Jurassic rocks in these islands reposes on the Torridon sandstone of Cambrian age; and the author discussed the

: question whether or not the intervening beds have ever existed in this locality, and came to the conclusion that they probably existed, and have been swept away by denudation. He remarked further upon the resemblance in lithological characters of the beds described to the corresponding deposits elsewhere in Britain. The traprocks intruded between the Jurassic deposits he regarded as of postoolitic date. The paper was accompanied by lists of fossils and descriptions of some new species prepared by Mr. Ralph Tate.

2. "Observations on the more remarkable Boulders of the North

west of England and the Welsh Borders." By D. Mackintosh, Esq., F.G.S.

In this paper the author described the situation and indicated the probable origin of many of the more striking known boulders in Westmoreland, Cumberland, Lancashire, Cheshire, and on the borders of Wales. The northern boulders seem to have originated chiefly from Wastdale Crag, Criffel, Ennerdale, and Eskdale; those of Cheshire chiefly from the Lake district and south of Scotland; and many of those on the Welsh borders from the mountains of Wales. Many of the boulders noticed by the author exhibit glacial striæ. The author also especially referred to the occurrence of boulders at high levels.

March 12th, 1873.-Joseph Prestwich, Esq., F.R.S., Vice-President, in the Chair.

The following communications were read :—

1. "Note on some Brachiopoda collected by Mr. Judd from the Jurassic Deposits of the East Coast of Scotland." By Thomas Davidson, Esq., F.R.S., F.G.S.

In this note the author stated that four species of Brachiopoda collected by Mr. Judd were especially worthy of notice, two of them being quite new, and two new to Britain. Three of them were obtained from the equivalent of the Kimmeridge Clay, which was the more remarkable as the Brachiopoda of that formation are comparatively few. The new species described were Rhynchonella Sutherlandi and Terebratula Joassi, derived, with Terebratula humeralis, Röm., from the Upper Oolite of Garty in Sutherland; the fourth species is Terebratula bisuffarcinata, Schlot., from the Lower Calcareous Grit of Braamberry Hill. This note is intended to form an appendix to Mr. Judd's paper on the Secondary rocks of the east coast of Scotland, and is accompanied by a plate.

2. "On Solfataras and deposits of Sulphur at Kalamaki, near the Isthmus of Corinth." By Prof. D. T. Ansted, M.A., F.R.S., F.G.S.

After noting the traces of volcanic action east of the Pindus chain, the author described the Solfataras and sulphur-deposits of the neighbourhood of Kalamaki as furnishing indications that there is even now a real though subdued volcanic energy in this part of Europe. At this place, about three miles east of the Isthmus of Corinth, there is a series of cream-coloured and grey gypseous marls, broken

by narrow gorges and fissures. These marls, the stratification of which is much disturbed, are loaded with sulphur. In the principal gorge there are several lateral fissures, forming caverns, communicating with the interior by deep cracks; these caverns are completely lined with crystals of sulphur and other volcanic minerals, and are rendered inaccessible by the large body of hot stifling vapours constantly emitted through them. The temperature of this vapour, where it can be reached, is about 100° F.; but the floor of the caverns is too hot to stand on, even near the entrance. The author is of opinion that the rocks in this gorge might be profitably worked for sulphur. Similar phenomena occur in several other places within about a mile of the ravine described; and the author was informed that this was the case also several miles further to the east.

The author adverted to other signs of volcanic action to the west of these solfataras, and especially to the structure of the Acropolis of ancient Corinth, and inferred that lines of volcanic action parallel to the spurs of the Alps of which Etna and Vesuvius and Santorin are the modern vents, ranged far to the north at no distant period.

3. "On the Origin of Clay-Ironstone." By J. Lucas, Esq., F.G.S.

The author commenced by giving a general view of the varieties, chemical composition, and mode of occurrence of Clay-ironstone, and suggested that the formation of all the bedded varieties may be explained by the supposition that they originated in peaty or nonpeaty lagoons on the alluvial flats of the deltas of the Carboniferous formations, which would present semiterrestrial conditions-that is to say, a surface exposed to the air, but subject to be covered by floods. Carbonic acid (formed in the lagoons from decomposing vegetable matter) meeting with protoxide of iron in solution, would unite with it to form carbonate of iron, which, with the mud of the lagoon, would produce Clay-ironstone. Thus, in the author's opinion, the beds of Clay-ironstone, like Coal-beds, mark terrestrial horizons. The author supported his views by reference to various sections, and also cited the occurrence of what he regarded as an analogous phenomenon on a small scale in some mud obtained from the shore between Redcar and Saltburn.

4. "Note in vindication of Leptophlæum rhombicum and Lepidodendron gaspianum." By Principal Dawson, LL.D., F.R.S., F.G.S. This note accompanied some photographs of the remains of plants referred to, and was in opposition to the identification of these remains with the Lepidodendron nothum, Unger, as proposed by Mr. Carruthers in his Appendix to Mr. Daintree's paper on the Geology of Queensland. The author maintained that his Lepidodendron gaspianum is distinct from Unger's species, although nearly allied to it, and that his Leptophloum rhombicum differs from both generically and specifically. He tabulated as follows the characters of his two species::

« PreviousContinue »