both these contrivances, and from every optical instrument with which I am acquainted, the kaleidoscope appears to differ essentially both in its effect and in the principle of its construction.

"As to the effect, the thing produced by the kaleidoscope is a series of figures presented with the most perfect symmetry, so as always to compose a whole, in which nothing is wanting and nothing redundant. It matters not what the object be to which that instrument is directed; if it only be in its proper place, the effect just described is seen to take place, and with an endless variety. In this respect the kaleidoscope appears to be quite singular among optical instruments. Neither the instrument in Bradley, nor the theorem in Wood's book, have any resemblance to this. Next as to the principle of construction, Dr. Brewster's instrument requires a particular position of the eye of the observer of the object looked at in order to its effect. If either of these is wanting, the symmetry vanishes, and the figures are irregular and disunited.

For these reasons, Dr. Brewster's invention seems to me quite unlike the other two."

Perhaps we could scarcely have a stronger proof of the novelty of the invention than the effect which it produced when it was first exhibited in London; both the scientific and the unscientific were equally amused and surprised at its effects; and although the principle on which it acts was easily perceived to be one with which we were familiar, yet the mode of its application was what no one had before witnessed.

The Editors have also received the following notice respecting the kaleidoscope, which they subjoin, as tending to complete the history of this curious instrument, and to show what approaches had been made to the invention by the older writers.

On the Kaleidoscope.

In Kircher's Ars Magna Lucis et Umbræ, published at Rome in 1646, there is an account of the experiment, which has of late created so much amusement, under the name of the kaleidoscope. At p. 890 of that work is a description of the appearance of the circle divided into its aliquot parts (which Dr. Brewster's tube so beautifully exhibits), by means of two plane mirrors, which are set at the angles of 120°, 90°, 72°, &c. &c. with one another. He afterwards goes on to describe the multiplication of images by reflections from mirrors, set in different situations with one another, and expressly mentions the variety of combinations which may be produced by changes in the objects which are reflected. Kircher claims the experiment as his own, saying that he had not heard of its having occurred to any one before him.

S.

ARTICLE XVI.

ANALYSES of Books.

Transactions of the Geological Society. Vols. III. and IV.

THE interest and importance of these volumes demand a far more extensive analysis of their contents than is consistent with the plan of our journal. We trust, therefore, that our readers will consider the following abstracts as intended rather to excité than to satisfy their curiosity.

1. Vol. III.-A_Sketch of the Mineralogy of Sky. By J. M'Culloch, M.D. F.L.S. &c.

7. Vol. IV.-Corrections and Additions to the Mineralogy of Sky. By the Same.

The longitudinal extent of this island is from S.E. to N.W. and its general figure is very irregular, being indented deeply on every side by bays and sea-lochs. The south-eastern extremity (consisting chiefly of the district of Sleat) is composed of gneiss, passing by insensible gradations into chlorite state, and of micaceous schistus. The beds rise to the N.W. at an angle varying from 30° to 50°, or even more. At Loch na Daal they pass into the sea, and may be observed to emerge at Glen Elg, on the main land of Scotland, precisely in the prolongation, to the N.E., of their line of run. To the N.W. of these beds, and extending beyond them in a N.E. direction to the extremity of the island, is a series of beds, which, where they touch the gneiss, are nearly vertical; they then become irregular, and, as their distance from the gneiss increases, rise on the whole towards the S.E. but with various local irregularities. This series consists of red sandstone, of an indurated sandstone, generally blue or grey, but occasionally brown, and sometimes including grains of felspar, of greywacke schist, and, in one place, of pure, compact quartz. The sandstones and schist repeatedly alternate. The red sandstone is the predominant member of this series, and in mineral characters corresponds with the red sandstone, which in Scotland occupies an interme diate place between the primary rocks and those which contain organic remains. Near the Point of Sleat, however, according to Dr. M. this series of slate and of red sandstone passes by degrees into a variety of gneiss, the former of these beds becoming a green, glossy, chlorite slate, and the latter assuming the appearance of a compact quartz containing grains of red felspar.

The newest beds of the sandstone just described, that is, those which lie the furthest to the N.W. rise at an angle of not more than 10°, and are covered by a deposit of limestone rising like them to the S.E. but at an angle not exceeding 5o. The outburst of the limestone may be traced in a direction N.E. and S.W

from Broadford to Loch Eishort. This limestone deposit consists of numerous alternations of limestone, shale, and sandstone, and contains gryphites, ammonites, and belemnites; it is, therefore, probably the same as the lias of England, and of the N.E. coast of Ireland. In many places these beds are penetrated, and more or less covered by sienite and other trap rocks. Where this is the case, remarkable changes appear to have taken place in the strata, for which no obvious cause exists except the proximity of the trap. The limestone becomes more crystalline, the organic remains become more rare, and where the utmost change has been effected, a perfect granular marble, without any visible organic remains, is the result, not differing in its external characters from that highly crystalline limestone, or marble, which geologists have been in the habit of considering as one of the primary rocks. The sandstone undergoes analogous changes, being converted into quartz more or less compact; and the shale becoming hard, compact, and brittle, is converted into lydian-stone.

The limestone deposit is covered by calcareous white and grey sandstone, which at Strathaird is intersected by a multitude of vertical dykes of trap without having its stratification materially disturbed.

The northern and western part of the island, as far as it has been examined by Dr. M. consists chiefly of trap, amorphous, tabular, or columnar, and resembling greenstone in composition, except that augite, instead of hornblende, forms one of its constituent parts. In many places it is amygdaloidal, and contains, besides the more common minerals of the zeolite family, magnificent specimens of laumonite and needlestone. On the northeastern coast it is combined with the lias and other stratified rocks in an infinite variety of ways, the study of which is highly instructive, as it throws much light on many disputed points. "All these irregularities occur in a mass, which, taken in a general view, has the character of a stratified trap, since, notwithstanding these irregularities, it bears a strong parallelism to the already parallel strata with which it is associated. It is abundantly plain that the appearance of stratification in the trap is here the result of the forms of the rocks on which it is placed, or among which it has intruded, in the former case surmounting them, and in the latter appearing to alternate with them. The instances of this apparent alternation are highly interesting, from their great extent, as well as from the perfect conviction which they present of the fallacious nature of this supposed connexion. In many cases the alternations of trap are as regular, as decided, and as evenly parallel as those of the stratified rocks themselves, the sandstone and limestone among which it lies. Yet in no instance does it not happen but that at some point or other the alternating bed of trap will detach an intersecting vein, unite itself to the superincumbent mass, or,

quitting the interval between two given beds of limestone, or sandstone, make its way across the one immediately above or below, and then proceed with a regularity as great for another long space between some other pair of proximate strata. In one or more instances I have observed this to happen after more than a mile in extent, throughout all which space not the minutest irregularity had appeared to indicate any thing else than a perfectly conformable and alternating stratification."

The middle district of the island lying between the trap and the stratified rocks already mentioned, contains the Cuchullin hills, the most lofty and remarkable in their outline of any of the mountain groups of Sky. The spiry forms of their summits, their hard, serrated outline, the huge, and somewhat curvilinear sheets of rock, that extend from their base to their summit, almost unalterable by time and weather, and absolutely barren, point out, even at a distance, that the rock of which they are composed is very different from the surrounding and adjacent trap and sienite. On a near inspection, it is found to consist of hyperstene, in grains or crystals, mixed in some parts with compact, green felspar, and in others with crystallized, white felspar, somewhat glassy.

3. On the Geological Features of the North-eastern Counties of Ireland, extracted from the Notes of J. F. Berger, M.D. &c. with an Introduction and Remarks by the Rev. W. Conybeare. Descriptive Notes, referring to the Outline of Sections presented by a Part of the Coasts of Antrim and Derry, collected by the Rev. W. Conybeare, with Observations by the Rev. W. Buckland, Reader in Mineralogy to the University of Oxford.

A right line drawn from Dundalk to Londonderry, and the curve of the coast from Londonderry back again to Dundalk, will include somewhat more than the district described in these papers. It may be considered as composed of three systems of mountains. Of these, one occupies the country lying south of the Belfast River and Loch Neagh. The Mourne mountains are its most elevated summits, and consist principally of granite. Hornblende rock and primitive greenstone appear on the skirts of the granite; and at a greater distance from the central nucleus, the greywacke formation is the prevailing rock.

The second system has for its eastern boundary a line drawn nearly N. and S. from the mouth of Loch Foyle to the parallel of the northern extremity of Loch Neagh, and extends westward to Donegal Bay, including the whole line of coast from Loch Foyle to Donegal. This tract consists principally of mica slate.

The third system occupies the whole country lying east of a line. drawn from the entrance of Loch Foyle to the southern extremity of Loch Neagh. The prevailing rock in this district is basalt; but other rocks, from mica slate upwards to chalk, make their appearance, especially on the coast; and from their various relations with the basalt, throw much light on the history

of this latter rock. The most important of these beds are the lias and the chalk.

The lias here, as in England, consists of beds of slate clay, alternating with thin beds of bluish, argillaceous limestone. Its characteristic fossils are ammonites, gryphites, and the columnar joints of the pentacrinus. In many places it may be clearly be observed emerging from below the green sand, and rests on red marl containing gypsum. At the peninsula of Portrush it comes in contact with tabular and prismatic greenstone, being covered by, and appearing to alternate with, this rock. Under these circumstances it assumes the appearance of a very compact and highly indurated, flinty slate, retaining, however, numerous impressions of ammonites, which sufficiently identify it with the slate clay of the lias, altered by the action of the greenstone.

The beds of oolite and calcareous standstone, &c. which in England intervene between the lias and the green sandstone, have not been observed in this district; the latter rock, therefore, rests immediately on the lias. It is not materially different from the green sandstone of the English series.

The chalk of this district, although perfectly identified, geologically speaking, with the chalk of England, by its relative situation in the series, and by the organic remains which it encloses, differs, in the following particulars, from the usual appearance of this substance. It is harder, and its texture is more compact. It is covered, and often intersected by basalt; in the latter case, and near the plane of contact, the chalk is converted into a dark-brown, crystalline limestone, which, as it recedes from the basalt, becomes more fine grained, then of a sandy aspect, afterwards porcellanous, and at the distance of eight or ten feet from the basalt is not to be distinguished from ordinary chalk. The flints in the altered chalk usually assume a grey, yellowish colour, and the chalk itself, when exposed to heat, is highly phosphorescent.

(To be continued.)

ARTICLE XVII.

Proceedings of Philosophical Societies.

ROYAL SOCIETY.

April 23.-Dr. Wollaston communicated a paper by Dr. Andrew Ure, entitled, New Experimental Researches on some of the leading Doctrines of Caloric, particularly on the Relation between the Elasticity, Temperature, and latent Heat of different Vapours, on thermometrical Admeasurement, and on Capacity.

April 30.-The reading of Dr. Ure's paper was finished. It