this change in the circulation, rather in the face than elfewhere, he cannot pretend to fay; - which naturally re minds a reader of the great humility and ingenuoufnefs of the most ingenious men, and of the honeft fimplicity of Horace

in his

Quae non didici planè nefcire fateri.

This doctrine of a ftimulus is fo obviously extendible to the actions of the organs of generation in both fexes, that we may well dispense with a further enumeration, or even abridgement, of them.

In his feventh very curious and diffufe fection, of the motions of the pupil and muscles of the internal car, after obferving the neceffity of contracting and dilating the pupil, in order to diftinct vifion, and an accurate defeription of the circular and radiated fibres of the iris, which answer thofe purposes, he remarks, that dilatation is the natural ftate of the pupil, as the longitudinal fibres are evidently ftronger than the circular; the contracting power of which is excited by the ftimulus of light, and augmented or remitted by the various degrees of it. This however he does not attribute to the immediate effect of light on the fibres of the uvea or iris, but in confequence of its affecting the very tender membrane of the retina; a certain proportion of light being neceffary to produce its regular function, and an extreme degree impairing it, and exciting an uncafy fenfation in it This doctrine is confirmed by fome very curious, eafy and fatisfactory experiments; and accounted for from an observation, that the optic nerve, and the nervous fibrills of the uvea, arife from different parts of the brain, and have no communication in their progrefs to the eye; whence the light, that affects the retina, cannot affect the pupil from any commerce between their nerves, but the uneafy fenfation in the retina, from too much light, may excite the fentient principle, ever prefent and ready to act at the origin of the nerves, to determine the nervous influence into the sphincter pupilla, to mitigate the offending caufe, by a contraction of it; as in a fainter degree of light it ceafes to act this mufcle, and allows the curtain of the pupil fuch an aperture from the natural action of its longitudinal fibres, as admits a commodious quantity of this fubtile fluid. And this difpofition, or faculty, of the fentient principle our author illuftrates, by the experiment of placing a lighted candle before the eyes, when, upon covering one, the pupil of the other is imVOL. VI. mediately

mediately dilated. This he obferves to be inexplicable upon mechanical principles, as their nerves and blood-veffel's have no other connexion, than in iffuing from the fame brain and the fame aorta; and the candle, the mechanical caufe of its contraction, acts with undiminished force. But admitting the contraction of the pupil from the energy of the mind, in confequence of the fenfations excited in the retina, it follows, that the mind no longer excited to contract the pupil covered from the light, and then in its natural dilated ftate, the pupil of the eye expofed to the light is dilated from the meer force of that conftant habitude of our moving both eyes alike, and contracting their pupils at the fame time. For tho' the motions of thofe organs be voluntary, the mind may, according to his eighteenth principle, lofe the power of moving the voluntary mufcles, except in a particular way. This principle, however, is to be admitted with fome reftriction; fince, tho' there is a remarkable uniformity between the motions of each pupil, that exposed to the light is obferved to be fomewhat lefs than the other; tho' neither is as much contracted, as if both were equally affected by light.' But however our author terms the motions of our eyes voluntary, it seems that the great contraction of the pupil depends principally on the timulus of light, as we fuppofe no one can look up at the fun, or any very luminous object, with a dilated pupil, whatever inclination he has to do it; for in this cafe the force of the fimulus muft operate more potently than our contrary volition.

Dr. Whytt, after employing fome pages in pointing out the errors of fome writers on the causes of the motions of the pupil, confirms his own theory by a remarkable hiftory, and fome judicious reflections on it.

Our learned author next afferts, that the motions of the pupil are as neceflary to the diftinct vifion of objects at different diftances, as to adapt the eye to different degrees of light. This he illuftrates by feveral curious and eafy autoptical experiments, many of which a reader may obferve in his own eyes, as probably the doctor did. He affirms, that in order to the diftinct vifion of near and lefs luminous objects the contraction of the pupil is neceflary; and this contraction refults principally from an effort of the mind; tho' in the viewing of diftant objects, the dilatation of the pupil is entirely determined by the quantity of light applied to

the

the eye. In short, as he had before premifed, the motions of the fibres of the uvea are of the mixed kind, being involuntary with regard to the ftimulus of light, and fometimes moderated by the intervention of the will, tho' not al-ways attended with a confcioufnefs of volition.

In obferving the greater dilatation of the pupil in infants, from the lefs tranfparence, and greater thickness and flatness of the cornea, thro' a deficience of the aqueous humour, whence the rays of light are lefs tranfmitted to the retina, he takes no notice of that exquifite membrane, the velum pupillae, which has been demonftrated to exift in foetuffes, and which perhaps is not wholly effaced very foon after the birth, but may remain for fome little, time to defend the exquifitely tender and medullary retina from the ftimulus of light.

He obferves next, that in a paralyfis of the longitudinal fibres of the uvea, while the circular ones retain their ufual force, the pupil will be always greatly contracted; whence the patient, being able to fee only in a great light, will have the nuspazi,a remarkable inftance of which the doctor fubjoins. And on the contrary, if the circular fibres are deprived of their energy, the pupil thence being much dilated, the eye will not be able to bear a great light, and being ufeful only in a faint one, the patient will fee beft in the fhade, or by a candle, which is that morbid affection of the fight termed by the Greeks νυκταλοπια.

The motions of the mufcles of the internal ear follow, as a fhort appendage to the section of the motions of the pupil. And here our author obferves, that the ear must have been incapable of diftinguishing a diverfity of founds, were not fome of its parts capable of various degrees of tenfion; for as a mufical chord of a certain length and tenfion can vibrate harmonically but with one particular found, if there was no mechanifm, by which the membranes of the tympanum and feneftra cvalis could be variously stretched or relaxed, they could be harmonically affected but by one found, and have only a more or lefs confufed perception of others. As the doctor very justly obferves, it may well appear wonderful how the ears fhould be fo adapted, by the actions of its mufclee, to fuch a vaft variety of founds; but with what exquifite fkill and amazing wifdom, fays he, is every thing in the animal frame adjufted! Here the ftimulus of found on the auditory nerves excites the mind to adapt,

by the influence of the nerves, the mufcles of the ear to fuch a contraction of its membranes, as fhall vibrate harmonically with the found; as the ftimulus of light excited it to an analogous action of the pupil: yet tho' the fentient principle thus fuperintends and adjufts these motions, the motions themselves, as he obferves, are not only unattended with confcioufnefs of volition, but are altogether neceflary and involuntary; as we cannot move these muscles when found does not ftrike the ear, nor prevent their action when it does.

[To be concluded in another article.]

K.

ART. XXIII. The Hiflory of the Portuguefe, during the rein of Emmanuel: containing all their difcoveries from the coaft of Africk to the farthest parts of China; their battles by Sea and Land, their fieges, and other memorable exploits : with a defcription of thofe countries; and a particular account of the Religion, Government, and Customs of the Natives. Including alfo their difcovery of the Brazils, and their wars with the Moors. Tranflated from the latin of Jerome Oforio, bishop of Sylves. By James Gibbs. 8vo. 2 vols. IO S. Millar.

IT

T feems almoft incredible how far the human mind is capable of being dilated, and the virtues of magnanimity and courage improved, by a feries of fuccefs; while a train of misfortunes, on the contrary, feldom fails to fink its faculties, even below contempt. Whoever doubts the truth of this obfervation, may read the Hiftory we are now to give an account of, where he will find the Portuguese acting like heroes of the first rank, and performing exploits not eafily, at firft view, to be credited. What shall we think of an handful of adventurers routing numerous armies, and a few hundreds putting many thoufands to flight? Nothing animates a people more than fending out colonies, and making new fettlements. The undertakers are often under

a neceffity of enduring the greatest hardships, and obliged to exert the utmost efforts of valour; and being thus inured to look down on dangers with contempt, they not only attempt, but perform actions, the very thoughts of which, in other circumstances, would have filled them with terror.

One can hardly read this hiftory, without calling to mind the fabulous ages of antiquity, when every thing was full of the marvellous. Befides, is it not reafonable to fuppofe, that the Portuguese would relate their own exploits in a man

ner

ner the most favourable to themselves? and we kewife with the good bishop of Sylves, may not appear to have complied a little with the legendizing fpirit of his religion : But be this as it will, there is, however, no doubt that the Portuguese were, during the reign of Emmand, in the meridian of their glory.

We fhall now proceed to lay before our readers a fummiry of the tranfactions of this reign, the fubject of the two volumes before us. We fhall fay nothing as to the merit of the prefent tranflation, which the reader will be fully apprized of from the extracts to be given.

As to method and difpofition, the whole is fubdivided into twelve books, fix to each volume, which ve fhall confider in order. The first book, after a judicious and appofire exordium, fets out with narrating the death of John II. of Portugal, in 1495. who, according to the character there given of him, must have been a prince of great ability, penetration, and fpirit. To him fucceeded Emmanuel, a prince of equal capacity, and rather more enterprizing than his predeceffor. Emmanuel began his reign with fettling the affairs of his kingdom, and regulating the courts of juice. He likewife gave a proof of his humanity, by reftoring the Jews to liberty.

As the war carried on by the Portuguefe in Africa, makes a confiderable part of the tranfactions of this regn, it will be proper to inform our readers of the ftate of their affairs, and the footing they had there. Ever since John the first had taken Ceuta, a very frong town in Barbary, fituate upon the freights of Gibraltar. His fucceffors never allowed. the war against the Moors to lie long dormant. Alphonfo, grandion to John I. and father to John II. had likewife taken the city of Tangier, together with Arzila, not far diftant from thence. And John too, after his father's death, tho' he was involv'd in great difficulties, always perfifted in a firm refolution of carrying on that war: and Emmanuel, following their example, embarked in it with vigour and fpirit.

The right revd, author of this hiftory relates many exploits of his countrymen during this reign, which, tho' poffible, certainly feem highly improbable. For inftance, that 200 Portuguese horfe might have defeated 2000 Moorish horfe, and 800 fot, we allow; but that they fhould do this without the lofs of a man, can only be credited by thofe, who, like the pious bishop, looked upon this event as a reward from heaven, for Emmanuel's fettling a tenth of the