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minutes, the heavens in all their serenity. Our eye stretched over a vast extent of country, plunging at once upon the sea in the north, and upon the fertile valley of Caraccas in the south. The barometer stood at 30 inches 7. 6 lines; the temperature of the atmosphere was 13° 7'. We were at an elevation of thirteen hundred and fifty toises. An expanse of sea, of thirty-six Jeagues radius, is embraced in one view. Those who are apt to become dizzy on looking down great depths, should remain in the middle of the small flat on the summit of the eastern cupola of the Silla. The mountain is not remarkably high, being nearly eighty toises lower than that of Canigou ; but what distinguishes it from all the mountains I have crossed, is its immense precipice on the side of the sea. The shore forms but a narrow edging; and, in looking from the top of the pyramid upon the houses of Caravellada, the wall-sided rocks, by an optical illusion of which I have often spoken, appear almost perpen-. dicular. The true inclination of the slope appeared to me, by an accurate calculation, 53° 28'. The mean inclination of the Pic of Teneriffe is hardly 12° 30'. A precipice of six or seven miles, like that of the Silla of Caraccas, is a phenomenon much rarer than is imagined by those who traverse mountains without measuring their height, bulk, or declivity. Since the revival, in several parts of Europe, of experiments upon the fall of bodies, and upon their deflexion to the south-east, a wall-sided rock, two hundred and fifty toises of perpendicular height, has been sought in vain throughout all the Alps of Swisserland. The slope of Mount Blanc to the Allée Blanche does not make an angle even of 45°, although, in most geological works, Mount Blanc is described as cut straight down on the south:-p. 608.

It was night when they reached, in their descent, the savanna, which is more than nine hundred toises in height.

* As there is scarcely any twilight between the tropics, perfect day-light is followed by sudden darkness. The moon was in the horizon: her face was covered from time to time by heavy clouds driven by a cold, impetuous wind. The steep declivities, clothed with yellow, withered grass, were at one time wrapt in obscurity, then, suddenly illumined, they looked like precipices which the eye sought to fathom. We proceeded in a long file, endeavouring to assist each other with our hands, to prevent rolling down in case of stumbling. The guides who carried our instruments left us one by one to go and sleep in the mountain. Among those who remained, was a Congo negro, who excited my admiration by the skill with which he carried upon his head a large dipping needle, keeping it always in equilibrium, notwithstanding the great steepness of the rocks. The mist began to clear away from the bottom of the valley. The lights which we saw scattered beneath us produced a double illusion-the steeps seeming still more dangerous than they really were, and, during six hours of continual descent, we constantly fancied ourselves near the farm-houses at the foot of the Silla. We heard, very distinctly, human voices and the shrill tones of guitars. Generally speaking, so strong is the upward propagation of sound, that, in an: aërostatic balloon, the barking of dogs may sometimes be heard at the height of three thousand toises.'--p. 616. This last observation is very just. From the edge of the Table

Mountain,

Mountain, which is three thousand six hundred feet high, and the upper part of which rises perpendicularly at the distance of about a mile from Cape Town, every noise made in the town, and even the word of command on the parade, may be distinctly heard. Shakspeare therefore is probably more correct when he describes the crows and choughs from Dover cliff to shew "scarce so gross as beetles,' than when he says

- the murmuring surge
That on th’ unnumbered idle pebbles chafe,

Can scarce be heard so high.' The volume, concludes with some account of the attempts at: working the gold and silver mines of the Caraccas, which were soon abandoned from the slender indications of these metals, and the high price of labour; but M. de Humboldt thinks that the question whether the province of Venezuela possesses mines worthy of being worked is by no means decided ; and that although in countries where labour is dearer, the cultivation of the soil demands unquestionably the first care of government, the example of New Spain sufficiently proves that the working of metals does not always injure the progress of agricultural industry. "The highest cultivated plains of Mexico, (he says,) those which recal to the recollection of travellers the most beautiful fields of France and the south of Germany, extend from Silao towards the Villa de Leon : they border on the mines of Guanaxuato, which alone produce the sixth part of all the silver of the New World.

We have been copious in our extracts, in order more fully to exhibit M. de Humboldt's manner of treating his subjects. Being less scientific than the former part of the narrative, this volume is better adapted for the general reader; and, as M. de Humboldt knows so well to communicate an interest to every subject which comes under his view, we have very little doubt that his remaining volumes, which will conduct bis readers along the Oronoco, the Cordilleras of the Andes, and the elevated plains of Mexico, will rise in interest with the importance and grandeur of his subjecct.

Art. VII. A practical Inquiry into the Causes of the frequent

Failure of the Operations of Depression, and of the Extraction of the Cataract, as usually performed; with the Description of a Series of new and improved Operations, by the practice of which most of these Causes of Failure may be avoided. Illus

truted by. Tables of the comparative success of the new and old · modes of practice. By Sir William Adams, &c. London. 1817. THERE is less of the art of composition in this book than we

I usually meet with in the present day. The title-page has in 40 inconsiderable degree run away with the preface—and the decation with the subject and the supplement. The periods are,

Practice of great candmportant; "ited it with

in many instances, out of joint; the manner is too diffuse and desultory, and the pronoun of the first person somewhat more frequent in its appearance than is customary in the polished reserve of modern times. With all this, however, the work has a peculiar claim to attention, and we have read it with considerable interest. Its subject is highly important;' its questionable points are discussed with great candour; it is enriched with the opinions and practice of the best and most skilful authorities of every country, not ostentatiously paraded, but fairly brought forward and compared, for the purpose of stating their respective merits and defects, and of showing the necessity of some improvement in the best modes of operating for the cataract which have hitherto beeii devised; and it is rendered still more valuable by the author's ingenuous disclosure of the practice which he is well known to have applied with success to the blind pensioners of Greenwich Hospital, as well as in the private course of his professional engagements.

The definition of the disease called Cataract is thus given in the opening paragraph of the work:

The term cataract is of Greek derivation, and signifies an opacity either of the crystalline lens, its capsule, or the interstitial fluid contained between the lens and capsule, which is called the Humour More gagni, (Humor Morgagni) it having been first discovered by the eminent anatomist of that name. Cataract may exist in any of these parts separately, or they may all be at the same time opaque.' To which the author adds, (p. 4.) the capsule and lens are, however, much more frequently occupied by disease than the humour morgagni.

We suspect that a simple cataract of Morgagni's interstitial fuid is rather a speculative than an actual disease ; one that possibly may exist, rather tlran one that has been actually detected and described. Richter, so far as we are acquainted, is the only writer before Sir William Adams, who has ever noticed this species or variety; for at present we know not how to arrange it. The notice occurs, as in the volume before us, in the initiatory account of the disease, and is never touched upon or referred to afterwards. Nor do we recollect a single case of the kind described as an actual occurrence in any author whatever: and hence Plenck, who has made a very free use of Richter, and followed up the diseases of the eye through little less than six hundred distinct species, (to say nothing of the numerous varieties into which each of these species is still further divided, and who may therefore be conceived to have given all that is needful,' has omitted the interstitial cataract altogether.*

It * His definition being as follows._- Cataracta--est cæcitas, quæ ab opacitate lentis crystallinæ, vel ejus capsulæ, provenit.--Respectû sedis, quanı opacitas tenet, dividitur

cataracta,

It is singular that the term cataract, though, as our author observes, of Greek derivation, and certainly of considerable antiquity, is not to be found either among the Greek or Roman writers; the first of whom called the disease apochysis (ánó xuris) or hypochysis (únó xuris)—and the latter suffusio, which is the name employed by Celsus. Cataracta, however, is in frequent use among the Arabian authors, and is generally supposed to have been invented by Avicenna. That we derived it from the splendid caliphat of Bagdad there can be little doubt. The term cataract, however, does not exactly signify an opacity, as is stated in the definition before us, nor disturbance or confusion of the sense of vision, as is its common interpretation. Cataractes, or catarrhactes, (καταράκτης Or καταρράκτης,) whence tlie Latin cataracta, is a genuine Greek term, importing a gate or door, or the bar which fastens it and proves an impediment to its being opened ; and, as the eyes were called by the Greek philosophers the portals or windows of the mind,

Dicere porro oculos nullam rem cernere posse,
Sed per eos animum ut foribus spectare reclusis,

Difficile est--the elegant fancy of the Arabians applied the term cataracta to the disease before us, as forming a bar or shutter to those windows by which the mind obtains a view of external objects, or an external world.

One of the most difficult species of cataract to detect is that of the lenticular membrane or capsule, (the second of Plenck and of Sir William Adams,) when confined to its posterior part, or that immediately behind the lens itself, and which is hence, in a very considerable degree, concealed by it. From the depth of the opacity, covered by the healthy appearance and natural brilliancy of the lens, it is not surprizing that it should have puzzled many ophthalmists of considerable practice, and been mistaken by others for an amaurosis or gutta serena, and consequently, while admitting of cure, been abandoned as an intractable disease.

• The opacity of the anterior part of the capsule can at all times be easily distinguished; but the posterior opacity is not easily detected, and has been known to elude the careful examination of several very experienced oculists, by whom it has been mistaken for gutta serena; and, although this species of cataract is mentioned by authors, it may be doubted whether they were, in reality, practically, aware of its existence. Indeed, without the assistance of the belladonna, or some other application capable of dilating the pupil, which class of applicacataracta, 1. In crystallinam, si ipsa lens crystallina est opaca. 2. In capsularem, quain alii membranaceam vocant, si capsulæ crystallinæ lamina anterior, vel posterior, vel utraque, opaca redditur. 3. In s tallino-capsularem, si lens crystallina et ejus capsula simul opacagtur:

tions were known to the ancient writers, but have been revived only within these few years, it is difficult, and sometimes impossible, to distinguish it. Richter, Wenzel, and Scarpa, who have written so largely upon cataract, and have published cases of its varieties on which they have operated, have not recorded any instance of this remarkable species : in which the posterior part of the capsule is alone affected with opacity, while the anterior part of that membrane, and the crystalline l'ens, remain perfectly transparent. In this country, at least, there is reason to believe, that it was practically very little known previous to the publication of my work on Cataract, &c. in 1812, in which a case of this kind is detailed at length, in a gentleman who had been blind eighteen years, seven of which he had been under the care of an eminent and experienced oculist, who considered and treated the disease as, Gutta Serena.'-pp. 6—8,

We have no doubt of the correctness of this statement, so far as relates to our own country, and concede to Sir William Adams the merit of having first practically called the attention of the English profession to this peculiar species of cataract, though the quotation we have just made from Plenck is a sufficient proof that the disease had been long known, and its seat distinctly laid down by writers on the continent.

It was formerly supposed, by one or two writers, that the crystalline humour has no proper capsule, and that the only membrane which invests it is a duplicature, or anterior and posterior extension of the membrane which incloses the vitreous humour, and which is commonly described by the name of tunica aranea, or membrana hyaloidea ; but it had altogether escaped our attention that this anatomical mistake, as we must still venture to call it, had been unaccountably revived within the last five years by a distinguished surgeon of this metropolis, in a passage copied by the present writer, and plausibly asserted to be little more than a transcript from Anthony Maitre-Jan's Traité des Maladies de l'Oeil. It is not necessary to enter into the subject : the anatomy of the eye is too well known in the present day to render the point for a moment questionable ; and if it were not, the cloud of authorities brought forward by Sir William Adams, in proof that the lens has a tunica propria, and that the species of cataract before us is seated in the posterior part of that tunic, would impel us to banish all hesitation whatever.

But we mention the fact for two reasons. First, because an error upon this subject is of great iinportance in a practical point of view; and secondly, if the position could be sustained for a moment, that the investing membrane of the lens is nothing more than an extension of the investing membrane of the vitreous humour, no writer has hitherto explained the proper meaning of the term cataract, as technically employed, or the real nature and extent of VOL. XVIII. NO, XXXV. - L

the

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