« EelmineJätka »
other.” Orange and yellow were selected easily, and appeared very bright to him.
About six years since, whilst in good bodily health and vigour, his sight began to decline, and now, for some months past, he has been quite blind. The present appearance of the internal eye when examined with the ophthalmoscope is shown in figure 2. It is technically called white atrophy—that is, the blood supply to the optic nerve and retina is in some way cut off: in consequence the vessels are very small and nearly obliterated; the choroid coat is sharing the general disorganization.
These are only a few of the facts which have been brought to our knowledge in connection with the very interesting subject of colour-blindness.
EXPLANATION OF PLATE. Fig. 1. An enlarged view of the colour-blind eye free from other defect. The
outer dark-coloured ring is the iris. On looking through the pupil, the circular opening in the iris, with the opthalmoscope, we first see a bright pink background, the choroid coat ; this with the optic nerve constitutes the fundus oculi. The small and nearly centrally situated circular disc observed when the eye is turned a little inwards, is the optic nerve, and from its centre issues the vessels of the retina. Artery and veins closely accompany each other for a short distance, and then divide, first into two branches, one of which, with its vein, is seen to proceed upwards, and another pair downwards ; and after passing the margin of the optic nerve they diverge, and again subdivide, split up into numerous smaller branches, some of which come forward to the ciliary processes. The vascular choroid coat imparts the pink colour to the back of the eye, which is nearly all reflected to the eye of the observer. The only difference observed in the eye of the colour-blind is the paler appearance of the fundus, or choroid coat, and occasionally whitish interspaces indicative of a
small and languid blood supply. Fig. 2. Shows the internal eye in an advanced state of disease, and is drawn
from the eye of Mr. Butcher, who, it will be noticed, suffered from colour-blindness years before his disease deprived him of sight. It cannot, therefore, be supposed that his colour-blindness was in any way owing to the disease which destroyed vision. The pupil is nearly fully dilated, forming a part of the diseased condition ; consequently, a much narrower ring of iris is seen than is given in Fig. 1. The fundus oculi, choroid coat, is very deficient in blood, which gives the mottled appearance, and indicates a state termed atrophy, in which the optic nerve and vessels of the retina is seen to share the supply of blood to retina and choroid, being in some way impeded, or nearly cut off, probably by a tumour forming in the brain in close proximity to the optic nerves. In other respects, the gentleman was in good health, and it is impossible at present to say to what he can attribute his total loss of sight.
THE PHYSICAL GEOLOGY AND GEOGRAPHY OF GREAT
prodigious size. From a few tangible and undoubted facts, geologists have been able to deduce as it were a great scheme, the history of the world's life. It consists, no doubt, in great part, of speculations and theories, many of which, in the advance of science, may prove false ; but by continual observation and unwearied perseverance we are gradually arriving at the truth.
Scarce fifty years have passed since William Smith, “the father of geology,” laid the basis on which all modern discoveries have been founded, and what was once considered a useless and “dry” study, now interests not only the learned in science, but all classes of society, who are eager to obtain some knowledge of the structure and nature of the world they inhabit. The Government has for two or three years past—with great credit to itself-encouraged a taste for science among the working classes, by evening lectures from the professors in Jermyn Street, and the crowded benches of the lecture-hall show how well their efforts have been directed, A course of six lectures on the physical geology of Great Britain, lately delivered to working men by Professor Ramsay, and ably reported by Mr. Mays, is now before us. The subject is treated in a manner at once interesting, instructive, and worthy of the President of the Geological Society. The way in which the connection between the scenery and geography with the geology of our island is shown, forms one of the chief merits of Professor Ramsay's course. Those who have listened to the course, or read the report, cannot fail to find a new interest in the country around them. Go they to the mountains of Wales, the Highlands of Scotland, the downs of the English south coast, or the plains of East Anglia,all have a fresh beauty ; each valley tells its tale of denudation by some roaring sea, or elsewhere by a mountain torrent; here is evidence of a mighty iceberg, there the course of a great river. A pleasure before unknown is now found in climbing the hills of Worcestershire, or the noble
pass of Llanberis; for Professor Ramsay tells us something about each, as he opens to our view the waves that long since surged on Malvern's sides, and the glaciers slowly grinding out their road among the mountains
*“The Physical Geology and Geography of Great Britain.” A Course of Six Lectures delivered to Working Men in the Museum of Practical Geology, Jermyn Street, by Professor A. C. RAMSAY, President of the Geological Society. London : Stanford,
of Wales, leaving as their sole memento in these warmer days, the charming lakes and torrents so well known to the lovers of Cambria. Before, however, proceeding to these generalities, a lecture is devoted to the explanation of the nature of the two great classes of rocks, the Igneous and Aqueous, with the sub-class of Metamorphic rocks, which were changed after deposition by the sudden heat of liquid lava. The nature of denudation is also explained, and, in illustration of the enormous power of running water, Professor Ramsay alludes to the Niagara falls ; thus, “ denudation" in the geological sense of the word means the stripping away of rocks from the surface by some agent, so as to expose other rocks beneath. Now, water running over the surface, wears away the ground over which it passes, and carries away detrital matter, such as pebbles, sand, and mud; and if this goes on long enough, there is no reason why any amount of matter should not in time be removed. For instance, we have a notable case in North America of a very considerable result from denudation now being effected by the river Niagara, where, at the Falls, the river has cut a deep channel through the rocks about seven miles in length. The proofs are perfect that the Falls were once at the escarpment, which is at the lower end of what is now this long gorge ; that the river, falling over this ancient escarpment, by degrees wore for itself a channel backwards and backwards, about a hundred and sixty feet deep, through upper strata that form a great plateau.
Probable calculations show, that to form this gorge a period of something “like ten thousand years has been employed” The manner in which deposits of mud, clay, limestone, &c., have been formed, is carefully described. As an example of the immense amount of mineral matter which water may carry in solution from rocks, the springs near Bath are mentioned, which yield 181,440 gallons of water per day, holding in solution 3402 lbs. of salts, equal to 420 tons per year; a quantity sufficient, if compressed and solidified, to form a column 9 feet in diaineter and 140 feet high. Rivers, too, contain exceedingly large quantities of mineral matters; the Thames at Teddington carrying along in its waters an amount equal to 33,497 tons per annum. The second lecture is devoted to the geology of Scotland, the various phenomena of metamorphisin, and the nature of the igneous rocks. The various strata forming the surface of England and Wales, and their peculiarities of structure, form the subject of the third lecture. A very interesting ideal section is given, from Wales through Gloucestershire to the Eocene beds of Hampshire ; and the bearing of the geological structure of the country along the line of section upon its scenery is described : the clays forming plains; the limestone, hills with escarpments suddenly rising from the flat surface below, their faces being washed away by the geologist's giant “denudation."
Perhaps the most interesting lecture in the series is that in which Professor Ramsay describes, according to a view which he has lately advanced, the origin of the Scotch and Welsh lakes. For this purpose he takes us first to Switzerland. Here he shows us the snow-capped Alps, with their valleys each containing a great glacier. The glaciers are formed by the compression of snow, which accumulates in enormous masses on the mountain sides. Fresh ice is thus continually formed and