When I simply looked sensationally on this scene, the lower fog line on the water seemed like a distant water horizon, and all above seemed but a cloudy sky. So strong was this impression, as not to be essentially impaired by seeing, half buried in the fog, the sails of a river sloop, which looked as if resting in the cloud sky. This illusion seemed to lift the hill on which I stood, to a height greatly exceeding its actual elevation. The strong likeness of the fog boundary to a sea horizon rotated the apparent horizon, so as to make it dip much below the real one, towards the west; thus overcoming both my gravity sensibility and a familiar knowledge of the locality.

4. A few weeks since, in an early morning, when standing on the bow of a sail-boat in Newport harbor, I observed, during a thick fog, a singular apparent distortion of the water surface. The boat seemed to rest in a bowl or hollow of water, some four rods in radius. This bowl seemed bounded by a gently curved swell, which ran tangent to the apparent remote horizon. Thus the water around me seemed some four or five feet lower than the horizon water. This appearance I suppose to have resulted from the fog line along the water, looking like a dim distant horizon, and thus bringing the apparent limiting horizon circle much too near. This would make the apparent horizon dip below the true, and would thus give a false apparent level to the water as far in as to that point, where in looking down on it, the true level could be distinctly seen. The true and delusive levels seemed joined by a curved swell, the curve evidently depending on the height of the eye and the density of the fog. This observation, like the preceding, illustrates the power of our idea of a water horizon.

5. If we look at the moon when a little above the horizon, its apparent enlargement may, by the simple act of shading with the hand all objects below the moon, be proved to be due in great part to the effect of intervening objects in magnifying our idea of its distance. The disc seems then to undergo a striking contraction of size. On dropping the hand, the moon seems again rapidly to enlarge. I think the effect of this masking is to give an apparent diameter not quite so small as when the moon is on the meridian, but it does not lack very much of this result. It will be noticed too, that when we see the sun or moon in the horizon, through forest branches, especially when we are travelling in a railroad car, they seem remarkably dilated. The great number of intervening branches and trunks is clearly the direct cause of this illusion.

This reasoning applies directly to explaining the apparently ellipsoidal form of the sky dome. Seeing along the horizon many objects on which the binocular or perspective sensibility fastens to elaborate the sense of distance, the horizontal axis is

much elongated in appearance, while the vertical axis, having no intervening objects to aid, is seemingly shortened. Doubtless the cause assigned by Euler, or the absorption of light by its oblique passage through the lower or misty strata in the vicinity of the horizon, may have a considerable agency in this phe

nomenon.

6. I was once of a party to observe Saturn through the West Point equatorial, and the several persons observing declared that the apparent size of the disc was, according to one, the size of an orange, according to another, as large as a cart-wheel, &c. In this case, the lack of perspective makes the visual angle the sole guide, except the obscure sense of focalization by which the instrumental pencils may affect the eye. Hence the utter vagueness of all estimates of apparent size, which must depend on a baseless imagination as to distance.

7. In sailing on Boston harbor, I have twice seen the phenomena of diverging and converging rays, or what is commonly called "the sun drawing water," both towards the sun in the west and towards the point symmetrically below the horizon in the east. Clear as it was rationally, that these two ray systems were but the opposite perspective views of the same parallel beams of light, I could not by any effort make them seem so sensationally. The opposite ray systems would not blend and I could not make them seem connected. The visual thinning of each beam near the perpendicular made the connection wholly invisible and so completed the illusory projection of the beams on the sky-dome. Hence an apparent widening of each beam, as it receded from the sun or from the opposite point. This whole appearance shows a complete subjection of the mental to the apparent or pictorial.

8. The great power of the two eyes to determine distances by the convergence of their axes, was strikingly shown when I was observing the reflection of a gas-burner globe from a street window of the room in which I was during the decline of day in New York. When looking with both eyes, this reflection seemed firmly established just by a branch of a tree, some ten feet outside the window. On closing one eye, I found it easy to transfer the image entirely across the street, by a mere exercise of imagination. In fact, when using only one eye, the rigid stability of the binocular vision was gone entirely, and the apparent distance seemed almost to become the subject of direct volition.

9. If in looking out over a landscape, we, by lying down or otherwise, bring the line of the two eyes into a vertical position, the scene will be found to undergo some remarkable changes. Hills will seem to recede into the distance, so as to look like far off mountains. The perspective will be found to lose very much of its relief and we seem rather to be looking at a picture on a

huge panoramic canvas, than on an actual receding perspective. Our sense of the horizon is quite impaired and a strange whimsicality of look becomes conspicuous, if we observe thus steadily for some time. In looking thus over a sheet of water, bordered by land varying from 3 to 20 miles distant, I noticed the same hollowing of the water near by, as before mentioned in the case of fog on the water. This was clearly due to the same apparent recession of near objects towards the horizon bound, and a consequent dip of the apparent horizon. It is clear too that by bringing both eyes into the same vertical, the interocular base becomes nullified for distance gaugeing in the horizontal direction. Hence objects seem to recede to one general cylinder around you, and the perspective perception is exceedingly impaired. The case is thus almost one of monocular vision. The study of these changes of scenery by our simple rotation of the interocular base, is very interesting and instructive. It shows, not only the influence of this base in forming our perspective distribution of distances, but that our sense of the horizon is very dependent for its firmness and precision on our gravity sensibility in our ordinary erect position.

Various other facts illustrative of the general views presented might be instanced, but the above must now suffice.

ART. XXXV.-Biographical Notices of Edward Forbes and others; by WILLIAM JOHN HAMILTON, Esq.*

Gentlemen.-It now becomes my duty, in accordance with the practice uniformly adopted by my predecessors in this chair, to address to you some observations on the losses we have sustained during the past year, and it is with unfeigned sorrow that I have first to allude to one whose name can never be mentioned in these rooms without emotion. I need not say that I allude to Edward Forbes, who was endeared to us by every tie of social friendship and scientific merit, and who has been snatched away from us at the moment when he had reached the highest position his ambition could have coveted, or his admiring countrymen could have bestowed on him. Scarcely had a few short months intervened since he had been called by the universal voice of the science of Great Britain to fill the chair of Professor of Natural History in the University of Edinburgh, during which we were still regretting his departure from the metropolis, before we were astounded and overwhelmed by the unexpected announcement of his death. We felt not only individually that we had lost a valued friend, but that

From the Anniversary Address of the President of the Geological Society of London, of Feb., 1855.

those anticipations of a brilliant scientific career, justified by the position he had attained and by the opportunities placed within his reach were doomed to bitter disappointment. These reflections are most painful, and, were I to follow my own inclinations, I would willingly forego all further allusion to the subject; but such a course would be a betrayal of duty towards our departed friend, and would disappoint the justly-founded expectations which you entertain of hearing a more detailed account of the distinguished and amiable man whose loss we so deeply deplore.

EDWARD FORBES was born in the Isle of Man, in the month of February, 1815. He evinced, at a very early age, an unusual taste for the study of natural history, and began to form a small museum when scarcely seven years old. A few years later he commenced his geological studies with the perusal of Buckland's 'Reliquiæ Diluvianæ,' Parkinson's 'Organic Remains,' and Conybeare's 'Geology of England,' exhibiting at the same time a more than usual taste for drawing.

He visited London at the age of sixteen, and was then engaged in studying drawing under Sass, but this was not enough to occupy his eager and ardent mind. He proceeded in 1831 to Edinburgh, where he devoted his whole time and energies to the pursuit of his favorite subject of natural history, while professing to overcome his repugnance for the study of medicine, the ostensible object of his matriculation. But medicine as a profession had no charms for one whose whole soul was filled with a love of the beautiful, and with an intense admiration of the works of Nature in every varied form. He cultivated his taste for natural history under the able teaching of such men as Professors Jameson and Graham. He delighted particularly in the botanical excursions of the latter, who was accustomed periodically to lead forth his pupils to the Highlands; thus making Nature herself, in her truest and loveliest garb, afford the practical illustrations of the teaching of the class-room.

At this period of his life, scarcely a year passed without some botanizing or dredging excursion, and long before he arrived at manhood, he had made himself well acquainted with the Fauna of the Irish Sea, on the shores of his native island. At the age of eighteen, in company with a fellow student, he made an excursion to Norway, where he spent some weeks exploring the wild and romantic districts of the country, adding to his zoological and botanical observations. Already at this time Edward Forbes began to direct his attention to botanical geography, the forerunner of those deep and philosophical views respecting the geographical distribution of the Flora and Fauna of the world which he subsequently developed, and which constitute one of the most interesting and leading features of all his writings.

In 1835, Edward Forbes visited the Alps; in 1837 he was prosecuting his studies at Paris under Beudant, Prévost, Geoffroy St. Hilaire, and De Blainville, and in May of the same year we hear of him at Algiers; the result of this expedition was an account of the land and freshwater mollusca of Algiers and Bougia, published in the Annals of Natural History' for May, 1839.

With the same view of prosecuting his researches in natural history, he visited Styria and Carniola in 1838, his remarks on which were published in the 'Proceedings of the Botanical Society.' In the summers of 1839 and 1840 he delivered at Edinburgh, whilst still a student, a course of scientific lectures on zoology, as well as one of a more popular nature, in which he pointed out the bearings of zoology on geology. I mention this as a subject of peculiar interest to us, as indicating the commencement of those views which, by their subsequent development and their growing importance in the hands of Edward Forbes, have exercised such a beneficial and practical influence on the study of geology.

The time was now fast approaching when Edward Forbes was to find a wider sphere for the exercise of his brilliant genius. In 1841 he published his 'History of British Star Fishes and other Echinoderms,' a delightful volume, charmingly illustrated by his own pencil and from his own designs. There are many in this room who will recognize in these illustrations the same ingenious and playful fancy, and the same ready pencil which never allowed a sheet of paper to lie unused before him, while he had a chance of transferring to it the humorous and graceful forms which he realized without an effort, and almost without a thought. In this same year he obtained the appointment of naturalist to H. M. surveying ship Beacon, Captain Graves, then employed in completing the survey of the coast of Asia Minor and the adjacent islands: an appointment more suited to his tastes and to his talents could not have been devised. He had here full play for the prosecution of his favorite pursuits of botany, zoology, and geology. Already well acquainted with the flora and fauna of the European Continent and their geographical distribution, he had now an opportunity of tracing their further extension to the East, and of examining the first appearance of the Oriental facies which they put on in the eastern portions of the Mediterranean. Nor was Edward Forbes the man to neglect such an opportunity. During this and the following year he pursued his botanical and zoological researches with unwearied energy, assisted by Captain Graves, who omitted no opportunity of enabling his scientific friend and companion to avail himself of every occasion for observation which the service afforded. It was during his various excursions in the Beacon and her boats, that Edward Forbes followed out those researches with the dredge, amongst the islands of the SECOND SERIES, Vol. XX, No. 60.-Nov., 1855.

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