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this stone into crystalite. The fire applied to the crucible, containing fragments of the glass, had been raised very slowly, which I know to have been the case by some circumstances of the experiment. The glass had softened by the first application of heat, but had cryftalized again as the heat gradually rose; so that the subftance consolidated, while still fo viscid as to retain the original shape of the fragments; at the same time it acquired such infusibility as to resist the application of higher degrees of heat during the rest of the process.” P. 49.
The second part of this paper contains an examination of various specimens of lava, from different volcanos ; namely, 1. Lava of Catania ; 2. Lava of Sta. Venere; 3. Lava of la Motta di Catania ; 4. Lava of Iceland ; 5. Lava of Torre del Greco ; and, 6. Lava of Vesuvius, eruption 1785. But the narration of the experiments is preceded by a statement, with quotations, of the opinions of Dolomieu and Kirwan, relatively to the formation of lavas. These two gentlemen agree in believing, that lavas have never been acted upon by a heat of sufficient intensity to produce complete fusion, and endeavour, each by an hypothesis peculiar to himself, to account for their fluidity.
Sir James Hall's experiments were performed upon specimens collected by himself; not from the superficial scoria of lavas, but from their interior and more compact parts.'
“When," says he, “these solid lavas are compared with our whinftones, the resemblance between the two classes is not only striking at first sight, but bears the closest examination. They both confift of a ftony basis, which frequently contains detached cryftals of various sube ftances, such as white felspar and black hornblend. The analogy between the two classes seems to hold ihrough all their varieties; and I am confident that there is not a lava of Mount Ætna to which a coun. terpart may not be produced from the whinstones of Scotland.
6. This resemblance in external character is accompanied with an agreement no less complete in chemical properties." P. 57.
After the recital of the experiments, which we hope are accurately stated, this author proceeds to apply their resulıs to the explanation of various geological facts; and, lastly, concludes his paper with a table of the various degrees of fulibibilty of different specimens of lava,
IV. A Chemical Analysis of Three Species of Whinstone, and Two of Lava. By Robert Kennedy, M. D. F. Å. S. and F. A. S. Edin.
« On the oth of August last,” this author says, “ I announced to the society that I had discovered soda in several varieties of the whinstone of Scotland, and also in lava from Mount Æina ; but did not describe the various experiments to which these substances had been subjected in my examination of them."
The account of those experiments, with all the necessary particulars, forms the contents of the present paper. It appears from their results, that the contents of 100 parts of the basalt of Staffa, are, Silex
• 48 .
The ingredients of 100 parts of whin of Salisbury Rock, are,
1. - 3.5
98.5 The ingredients of 100 parts of whin from thé Calton Hill, mear Edinburgh, are, Silex
- 50 Argil :
- • - 4
98.25 The ingredients of 100 parts of the lava of Catania, Æina, are, Silex
= = = 9.5
- 4 Muriatic acid, about
. The ingredients of 100 parts of lava Sta. Venere, Piedimonyo, Æina, are, , 3 .
- 50.75 Argil .
• 17.50 Oxyd of iron
- 14.25 Lime
97.5 “ The results of these analyses show, that whins, and a certain class of lavas, taken from remote quarters of the globe, confift of the same component elements, united in each, nearly in the same proportion. The only circumstance in which they materially differ, is the loss of fome volatile matter in the fire, which is peculiar to the whins alone.
" We need not be now farprised at the facts mentioned by Dolo. mieu, and others, of soda being found about volcanos, or upon the surface of lavas; as it has thus been shown to exist in these substances in combination with their earthy bases,” P. 94.
After the account of those analyses, this author relates a va. siety of facts, which tend to prove, that whins and lavas are not the only stones which contain soda ; but that this alkali is widely diffused through the mineral kingdom.
V. A New Method of resolving Cubic Equations. By James Ivory, Esq.
As it is not practicable to abridge the contents of this paper, so as to convey a clear idea of the methods therein contained, we can only in general inform our readers, that this author divides cubic equations into two species ; namely, thofe which have three real roots, and those which have only one seal root ; and that their solutions depend upon the properties of certain geometrical lines.
This publication of the Royal Society of Edinburgh, contains only one plate,
Art. V. Memoirs relative to Egypt, written in that Country
during the Campaigns of General Bonaparte, in the Hears of 1798 and 1799, by the learned and scientific Men who accompanied the French Expedition. Published in Paris by Authority. . 8vo. 459 pp. 8s. Phillips. 1800.
IT is well known, that when Bonaparte undertook the com.
mand of the army of Egyp:, he induced a number of men of science to accompany him in that bold and memorable ex
pedition. Some of them were men of established celebrity; such as Bertholet and Dolomieu ; but by far the greater part were not distinguished in the annals of the learned.
When this is known, and when it is also considered, that the business and fatigue of war allow litile leisure for observations, experiments, or discoveries, and that a free communication with the inhabitants was cut off, and that it was even dangerous to go beyond the lines of the army, we shall not only be led to be moderate in our expectations as to the early acqui. fitions of these scientific adventurers, but hall also judge with candour and indulgence the part they have performed. .
The work before us consists of a fiumber of memoirs on different subjeds. These were brought by Bonaparte to France, presented by him to the National Institute, and gleaned, are ranged, and published by that body. The papers are numesous. They relate to objects of natural bistury, arts, antiquities, and the manners of the modern Egyptians. Some of them are interesting and well-written ; these we shall notice. Others are too hallily drawn up to prove satisfactory; and fome are below criticism. Our readers will doubtless pardon us for passing over these in silence.
The first of those papers which are interesting is by An, dreofly, on the preparation of gunpowder. In this we are informed, that the saltpetre, which is there obtained from trenches cut in the land, is very pure. The gunpowder is formed by means of manual labour, and is composed of 8 parts sals, petre, 2 of sulphur, and 2 of charcoal. This material is trie iurated in stone mortars. Each mortar contains 15 pounds of the material. It is grained by pressing it through a grating. To this paper succeeds one by Shulkonski, relative to the road from Cairo io lsalchkych ; and another, from the Physician in Chief to the Army, Desgeneties, to the medical men, recommending them to draw up a physico-medical topography of Egypt.
In the report on Pompey's Column, which follows, there is nothing interesting.
The next paper, which is by Monge, relates to a singular optical illusion, frequently met with in Egypt, called the mirage, of which the following description we hope will be ac. ceptable.
« The country of lower Egypt is nearly a level plain, which loses itself, like the sea, in the clouds at the extremity of the horizon : its uniformity is only interrupted by a few eminences, either natural or factitious, on which are Gtuated the villages, thus kept out of the reach of the inundations of the Nile ; and these eminences, less usual on the kirts of the desert, more frequently to be seen on the side of the Delta,
· and which appear like a dark line on a very transparent ky, are ron
dered still further visible by the date trees and sycamores, oftener to be met with in such firuations than elsewhere.
“ Both morning and evening the aspect of the country is exactly as it ought to be; and between you and the last villages which present themfelves, you perceive nothing but land; but when the surface of the earth is sufficiently heated by the rays of the sun, and indeed until it begins to get cold towards the evening, the land no longer seems to have the same extension, but to be terminated, to within the distance of about a league, by a general inundation.
« The villages placed beyond that, appear like so many islands ftationed in the midit of a great lake, from which the spectator is feparated by an extent of land, more or less considerable, according to circumstances. You chen behold the image of each of these villages reflected exactly as if it were exhibited on a clear surface of water, with only this difference, that as the representation is at a considerable distance, the smaller objects are invisible, and the masses alone diftinét; in addition to this, the edges of the reversed image are rather ill defined, and such as they would be if the surface of the reflecting medium happened to be a little agitated.
" In proportion as one approaches a village, which appears to be placed in the midst of an inundation, the margin of the water seems » to recede, and the arm of the sea, separating you as it were from the village, shrinks back by degrees : it at length disappears entirely, and the phenomenon which now ceases, in respect to the first village, is instantly reproduced by a new one, which you discover at a due dire tance in the rear. Thus every thing contributes to complete an illufion, which is sometimes cruel, more especially in the desert, becaufe it tantalizes you with the appearance of water, at a time when you experience the greatest want of that element." P. 75. .
The explanation of the phænomenon is not only ingenious, but also satisfactory ; it is too long however to be inserted, and cannot be well condensed.
The next paper is on the Wing of the Ostrich, in which the author, Geoffroy, proves a very great resemblance in general structure and habits between the ostrich and quadrupeds.
Then follows a paper on Opthalmia.
A paper on the mode of dying cotton and flax, by means of the Carihamus, although very short, is by no means uninterest. ing. The difference between the processes employed in Europe and in Egypt consists, ist, in using water, which is in a flight degree alkaline, to extract the yellow colour from the plant; 2ndly, bruising the Carthamus with woud alhes, that is, incorporating an alkali with the colouring matter, by means of mechanical power; and, 3dly, using warm water instead of cold, which is employed in Europe.
The next memoir relates to the Lake Menzaleh, and is written by Andreosly, General of Artillery. It is a long and