require some skill in walking not to sink in them; delights to the botanist, for their beauty far exceeds nay, even in some of the greatest thoroughfares, that of our northern plants; besides which, they are there is nothing on which the foot passenger can evergreens, and are exquisitely beautiful even in pass but a narrow path winding near the houses; winter. Of these heaths, one species grows to the and as all the carts keep as near to the houses as height of six feet, and, when in bloom, is entirely possible, in order to take the horses out of the deep-covered with red flowers, presenting a most lively est part of the mud, it often happens that the unfor- appearance; yet, notwithstanding all this profusion tunate passenger receives all the dirt and filth which of beauty, these solitary tracts soon become irksome is thus most lavishly splashed about. But the night to the traveller; for where the romantick and subis even worse; for though formerly the city was lime are wanting, no beauty of country can long be lighted, yet lately this practice has been laid aside; pleasing, unless intermingled with cultivation. and as it is the custom to close the window-shutters at an early hour, there is no light whatever to diversify these scenes of dirt and desolation; to which we must add the annoyance of whole troops of half-starved dogs, that are suffered to wander about like so many hungry wolves, and are often almost as dangerous as the ragged banditti who are suffered by the police to commit their depredations unmolested. The unfortunate stranger, too, is constantly pestered with whole hosts of beggars, a trade which seems not confined to any particular class of society, but is practised under various pretences by all:— one species of it is for the relief of souls in purgatory, for which purpose the religious fraternities are permitted to collect alms, the greater part of which they are said to apply to their own account.

Wretched as is the interiour of this proud city, yet its environs have a striking peculiarity of appearance; for the whole vicinity, to a considerable distance from Lisbon, is covered with large gardens, surrounded with lofty walls, between which it is most tiresome to travel even for leagues, in some directions, without being able to see any other object, and being in continual danger of mistaking the

road.

This taste, which is universal, has been justly distinguished as selfish and morose-oriental and Moorish and may probably have had its origin in their constitutional jealousy, which prompts them to choose a close fortification in preference to an open garden.

These extensive enclosures are called quinta, and they are often very large, and laid out rather for profit than for pleasure, containing within their walls plantations of orange and olive trees, and sometimes even corn-fields; they have, in general, a large garden-house situated at one end, where their owners and families are accustomed to spend part of their summer in almost monastick seclusion.

When the traveller penetrates into the interiour of the country, he soon observes that the great part of the eastern districts consists of extensive heaths, which have an undulating appearance, from the number of small hills with which they are intersected. The soil in most places is sandy, and swampy tracts are seldom found, as, in general, the extreme aridity of the soil is the cause of the great barrenness of these wide-extended plains and hills.

THE FIVE SENSES.

THE SENSE OF SIGHT.-No. 3. LAWS OF VISION. 6. DIRECTION OF VISIBLE OBJECTS.

The mind, in perceiving any point A of an object, (that of the pen's point, for example,) receives the

rays by which it is made visible at different degrees of obliquity; but notwithstanding the difference of these degrees, the object is seen only in the direction of the central ray A B; and this is always perpendicular to the retina. Now the surface of the retina being of a spherical form, it follows, that these rays being perpendicular to it, must invariably pass through a point which is the centre of the curve of the retina, and which is therefore called the centre of visible direction. This centre is a fixed point in the vitreous humour, and as it never changes its place, however great may be the rotation of the eye, it is evident that it must be the same with the centre round which the eye rolls when it is in motion. It results from this coincidence of the two centres, that the unvarying stability of the objects at which we look is preserved.

7. CAUSE OF ERECT VISION.

The humours of the eye acting like a convex lens, a picture of the object is painted on the retina in an inverted position. To young and uninformed persons this inversion of the image makes the cause of erect vision a subject of much difficulty and by some of the old philosophers it was considered as But the law of one of the mysteries of nature. visible direction makes the whole a matter of easy comprehension. It will be observed, that the rays of visible direction cross each other at the point or centre of visible direction; those from the lower part of the picture go to the upper part of the object, Notwithstanding this want of fertility and cultiva- and those from the upper part of the picture go to tion, it is extremely pleasant to traverse this part of the lower part of the object; and thus when the the country in the spring, when the beautiful varie- mind would perceive the top of an object, it refers ties of the heath plants, and the charming cisti of from the bottom of the picture upwards, and when it these southern regions are all in their highest bloom, would perceive the bottom of an object, it refers and the mild exhilarating atmosphere is filled with from the top of the picture downwards, whereby a innumerable perfumes. This variety of shrubs is true notion of the erectness of objects is obtained indeed uncommonly great, and presents a thousand (as, indeed, it only can be) by means of an inverted Cisti, (in the plural,) small sunflowers. (Cistus, singular.) picture.

8 ACCOMMODATION OF THE EYE TO DIFFERENT DISTANCES. | eyes lose the power of adjusting themselves to short distances. This afflicting disability usually arises from a flattening of the cornea, and from a relaxation in the structure of the crystalline lens, by which its power of acute refraction is lessened.

The rays by which vision is performed in reading a book, or paper, make, in falling upon the eye, a much greater angle than those would do which fall upon the eye in looking at a distant landscape; and this difference in the obliquity of the rays is followed by a difference of the degrees in which the two sets of rays are converged to a focus. The rays from the "Family Magazine," for instance, as they would form a greater angle, would also be converged to a focus sooner than those from the distant landscape; and consequently, if the retina was so situated as to receive the focus of rays from the book, the focus of rays from the distant landscape would be formed beyond it, and would therefore confound the eye with an indistinct image; but if, on the contrary, the retina was so adapted as to receive the focus of rays from the distant landscape, that from the book would not reach it, and would therefore be invisible. To meet these difficulties, the eye possesses a power of adjusting its different parts in such a manner to the distance of the different objects at which it looks, as always to cause the visual rays to converge to a point on the retina. These adjustments consist chiefly in an alteration of the convexity of the cornea, and a movement of the crystalline lens nearer to, or farther from, the pupil, by which the axis of the eye is made longer or shorter, and the degree of convergence greater or less as the occasion may require. These beautiful operations by use become involuntary, although they still continue under the dominion of the will, and can be performed or not at pleasure, as the reader may at this moment try for himself, by letting his eye, as he looks at the printing, relax into a state of repose, when the letters will immediately become indistinguishable, and appear as they do to an aged person. This state of repose is one natural to the eye, and in which it is adjusted to long sight, a faculty which most old persons possess; for we have observed that they can commonly distinguish all that to the strongest eye is visible, of a ship in the horizon, while at the same time they are totally unable to read the letters of a book.

9. CAUSE OF SINGLE VISION WITH TWO EYES.

11. CAUSE OF 3HORTSIGHTEDNESS. reverse of those which occasion longsightedness, Shortsightedness arises from causes exactly the excessive density in the structure of the crystalline namely, too great a convexity of the cornea, and an lens, by both of which the visual rays from near the retina. Both these distressing maladies have objects are converged to a focus before they reach however been kindly obviated by the direction of Providence in the invention of spectacles, which were first generally used in Holland in the fourteenth century. By these simple and invaluable instruments, longsightedness is corrected by the use of a convex lens, which converges the spreading rays to a focus on the retina; and shortsightedness, in like manner, by a concave lens, which diverges the rays, and prevents them from coalescing in a focus, before they reach the retina.

H

A

E

B

F

is prevented by the convergence of the visual rays to foci, at C, before they reach the retina at D.

A, a shortsighted eye; B, an arrow which it attempts to perceive, but

E. the same eye, similarly situated, showing how, by the intervention of a concave lens, G, the rays are diverged, and the image of the arrow, F, accurately converged to the retina at H.

MOTIONS OF THE EYE.

In looking at a telescope, our attention is arrested by the ease with which it is turned, at the will of the operator, from one object to another, and we readily perceive that without the aid of a number of adjusting wheels and screws, by which its motions are effected, the instrument itself would have been comparatively useless. It is just the same with the eye. We have seen that it is admirably contrived in all its parts for the production of vision, and we shall presently find that it is no less admirably furnished with the necessary apparatus for making its powers constantly available to our wants and wishes. Dr. More, in his "Antidote against Atheism," has quaintly, but prettily said, that "the eye in its structure is so perfect, that the reason of an atheist ought easily to have rested in the exhibition of its marvels, and without further inquiry, have passed from admiration of the contrivance, to worship of the Divine Contriver." But willing to accumulate the argument, he goes on to observe that "man being able to move his whole body upward and downward, and on every side, might have unawares thought himself sufficiently well provided for; but Nature hath added muscles also to the eyes, that no perOld persons are usually longsighted: that is, their fection might be wanting; for we have often occasion

Much time has been wasted and great ignorance exhibited, in the discussion of this subject; but as we now live in an age when an appeal to facts alone is allowed in the settlement of a proposition, it becomes one of very easy solution. By the aid of the straight muscles of the eye, we can direct the axis of each eye, so that when prolonged they may meet in any desired points beyond the distance of about six inches. Let this desired point be a lighted lamp at the end of a dark gallery, and let us direct our eyes to the lamp-a picture of it would then be formed on the retina of each eye; but because the lines of visible direction from any two corresponding points of the pictures meet on the one real point of the object, the two pictured points must of necessity be seen as one point; and the collection of points forming the picture of the lamp in one eye, will exactly coincide with the collection of points forming the picture in the other eye.

10. CAUSE OF LONGSIGHTEDNESS.

fying straight depressing muscle of the eye. Arises Side view of the Muscles of the Eye, in their natural from the spheroidal bone in the bottom of the chamber of the eye, and passing forwards and downwards, is inserted into the sclerotick coat, at the bottom of the eyeball. It will be observed that the direction and insertion of this muscle are exactly the opposite!

interesting in the body; and, as it offers a brilliant | "Nothing," he says, "can be more manifestly an example of the mechanical wisdom of the CREATOR, act of contrivance and design than the muscles of the demands our closest attention. It arises from the eye, admirably adapted to move it any and every margin of the whole in the bottom of the orbit which way; upwards, downwards, to this side or that, or transmits the optick nerve between the first and their howsoever we please, or there is occasion for, so as straight muscles. From thence it runs round the always to keep the parallelism of the eye which is neball of the eye, slantwise, to the great canthus, or cessary to true vision. For the performance of inner angle of the eyelids, in the upper side of which which service, the form, the position, and the due there is a cartilaginous ring, called the trochlea, strength of each muscle is admirable. But what is through which it passes like a rope over a pulley, most to be here noted is the exquisite equilibration and, turning backwards, it proceeds between the of all the muscles, effected partly by the equality of first straight muscle and the ball of the eye, and in- the strength, which is the case of the adductor and creasing in breadth, it is inserted into the sclerotick the abductor, partly by their peculiar origin, or the coat on the back part of the ball of the eye, near the addition of the trochlea, which is the case of attolens abductor. When it acts, it rolls the eye about its and deprimens. By this so curious and exact equiaxis, towards the nose, and at the same time draws libration, not only unseemly contortions, and incomit forwards, and turns the pupil downwards. modious vagations of the eye, are prevented, but also it is able with great readiness and exactness, to apply itself to every object.

"Seeing, then," says Ray, in his Wisdom of God in the Creation, "the eye is composed of so great a variety of parts, all conspiring to the use of vision, whereof some are absolutely necessary, others very useful and convenient, none idle or superfluous; who can but believe that this organ was designed and made purposely for the use for which it serves ?”

ABACUS.

The learned Dr. Paley, in speaking of a muscle of the same structure, which, in animals, assists in drawing a cleaning membrane over the eye to remove dust or other impurities, makes some valuable remarks, which, as they illustrate our subject, we shail quote. He says, after describing its "marvellous mechanism:""a muscle passed through a loop, and inflected, as if it were round a pulley. This is a peculiarity, and observe the advantage of it. A single muscle, with a straight tendon, which is the common form, would have been sufficient if it bad had power to draw far enough. But the contraction necessary to draw the membrane over the whole eye, required a longer muscle thar, could lie straight at the To give our readers an idea of the general conbottom of the eye. Therefore, in order to have a greater struction of these machines, and of the principles on length in a less compass, the cord of the muscle makes which it proceeded, we will select for explanation an angle, which perfectly answers the required end." that of Pascal, the earliest. Of those which have Now this is also strikingly true of the great oblique since been contrived, there are some which have muscle of the human eye-the end, and the means been considered to possess advantages over that in used for its accomplishments, being, in both cases, practice; but as the first of its kind, and as one precisely the same; for Cowper, in his Myotomia which may have served as a model to many of its Reformata, has remarked-"When any of the successors, it is the object of our preference on the straight muscles contract, they would draw the ball of the eye inwards by some equal force," which is exactly what the great oblique muscle, assisted by its lesser companion, which we shall presently describe, is admirably qualified to perform. The superiour strength of the straight muscles acting, be it observed, rectilineally, and with a short distance, is thus beautifully counterpoised by a simple mechanical arrangement, in which the power of a weak muscle is doubled, and the disadvantages arising from the obliquity of its course and the awkwardness of its situation, are actually made to assist the very operations which they might have been expected to impede.

2. OBLIQUUS INFERIOR OCULI, or the small sloping muscle of the eye. It arises from the lower edge of the orbit, on the side next the nose, and passing obliquely and somewhat transversely backwards, it slips under the deprimens, and, spreading into a flat tendon, is inserted into the back and outer part of the sclerotica, directly between the abducens and the optick nerve. Its office is to roll the eye about its axis from the nose, and, at the same time, to draw it forwards, and direct the pupil upwards.

EQUILIBRIUM OF THE MUSCLES OF THE EYE.

This subject has been so concisely and pithily discussed by Durham, in his Physico-Theology, that we shall content ourselves by simply extracting a a portion of his remarks:

present occasion.

The accompanying illustration exhibits a general view of the instrument with the operator at work at it, who has one hand employed in putting into motion one of the moveable wheels of the apparatus, and the other engaged in connecting the operations of the machine with the figures contained on the paper by his side. It consists of a box covered with a plate of metal, pierced on one side with several square holes, as represented in the figure On the

single pound on the divided circle of the next train. Notwithstanding the skill and contrivance bestowed upon instruments of a nature similar to that we have just described, their power is necessarily but very limited, and they bear no comparison either in ingenuity or magnitude to the grand design conceived, and nearly executed, by Mr. Babbage. Their very highest functions were but to perform the operations of common arithmetick; Mr. Babbage's engine, it is true, can perform these operations, it can also extract the roots of numbers, and approximate to the roots of equations, and even to their impossible roots; but this is not its object. Its function in contradistinction to that of all other contrivances for calculating, is to imbody in machinery the method of differences, which has never before been done; and the effects which it is capable of producing, and the works which, in the course of a few years, we expect to see it execute, will place it at an infinite distance from all other efforts of mechanical genius. Great as the power of mechanism is known to be, yet we venture to say, that many of the most intelligent of our readers will scarcely admit it to be possible, that astronomical and navigation tables can be accurately computed by machinery; that the machine can itself correct the errours which it may commit; and that the results, when absolutely free from errour, can be printed off without the aid of human hands, or the operation of human intelligence. "All this, however," says Sir David Brewster, in his entertaining Letters on Natural Magic, "Mr. Babbage's machine

opposite side of the plate are a number of toothed wheels, each moveable, and turning freely about its own centre. The first to the extreme right has 12 teeth; the second, proceeding from right to left has twenty, and all the others have 10. About each of these wheels an outer rim or circle is described on the surface of the plate, which circle is divided into the same number of equal parts as there are teeth in the wheel which it surrounds, and which is moveable, as it were within it. The figures corresponding to each of these points of division are inscribed on all the fixed circles, commencing with O at that portion of each which is nearest to the extremity of the side of the box on which they are placed, and proceeding round in the direction of from left to right. Passing over at each of these zero points of division, and attached to the surface of the plate, is a small tongue of metal which projects slightly over the enclosed wheel, so as not, however, to rest on or be in contact with it, but simply for the purpose of arresting the progress of the rod held in the hand of the operator, as seen in the preceding illustration, when engaged in imparting motion to any one of the wheels. From the number of teeth which we have given to those wheels, it is evident that the one to the extreme right, which contains 12, is intended for what may be termed a pence wheel; the second, which has 20, for a shillings wheel; the third, which has 10, for the units of pounds; the fourth, for tens; the fifth, for hundreds; the sixth, for thousands; the seventh, for tens of thousands; and the eighth, for hundreds of thousands. By en-can do; and, as I have had the advantage of seeing larging the machine, this number might be increased, and the power of the instrument extended.

We may now proceed to point out the internal arrangement of the machinery. Motion is communicated by the wheel and axis a b, which is furnished with a contrite wheel c. This actuates the next in the series which is placed in the opposite direction. On the same axis are placed two similar wheels de, the last of which gives motion to the wheel and barrel fg. There are two apertures in the upper plate A B, through which the figures on the barrel may be seen, so that the person who moves the wheel a may readily register the amount of motion, by observing the figures as they pass these apertures.

it actually calculate, and of studying its construction with Mr. Babbage himself, I am able to make this statement on personal observation." It consists essentially of two parts, a calculating, and a printing part, both of which are necessary to the fulfilment of the inventor's views, for the whole advantage would be lost if the computations made by the machine were copied by human hands and transferred to types by the common process. The greater part of the calculating machinery, of which the drawings alone cover upwards of 400 square feet of surface, is already constructed, and exhibits workmanship of such extraordinary skill and beauty, that nothing approaching to it has hitherto been witnessed. In the printing part, less progress has been made in the actual execution, in consequence of the difficulty of its contrivance, not for transferring the computations from the calculating part to the copper, or other plate destined to receive them, but for giving to the plate itself that number and variety of movements which the forms adopted in printed tables may call for in practice.

The practical object of the calculating engine is to compute and print a great variety and extent of astronomical and navigation tables, which could not otherwise be done without enormous intellectual and manual labour, and which, even if executed by such In the complete machine there are several of these labour, could not be calculated with the requisite actrains of wheels, and they communicate with each curacy. Mathematicians, astronomers, and navigaother by a small lever h, shown in the diagram. Now, tors do not require to be informed of the real value if we suppose the first of these barrels to have made of such tables; but it may be proper to state, for the an entire revolution, the two connecting bars ii, will information of others, that seventeen large folio have raised the lever and moved the communicating volumes of logarithmick tables alone were calculated wheel of the next train one tooth forward in its under the superintendance of M. Prony, at an enorcourse. If, for example, it be the barrel which re-mous expense to the French government; and that presents shillings, it will by this means indicate a the British government regarded these tables to be