of a similar agency, in opposition to the opinions of other observers, who had referred the formation of some to the decomposing action of the atmosphere on granite (aided in some instances by human agency), of others to the effect of glaciers, &c. 2. "On the Copper-mines of Namaqualand." By R. N. Rubidge, Esq., M.B. In a letter to Sir R. I. Murchison, F.G.S. On his examination of Namaqualand, in 1854, Dr. Rubidge found that the conditions under which the metalliferous rocks occur there differed from any which he had previously known, and that they did not take the character of lodes, as usually understood. On the contrary, he found that all the runs of ore, in at least the more southern part of this mining district, present externally an ironstained surface, the rock being different from the gneiss on either side, and that the general south dip of the rocks changes in the centre of the run to the opposite direction, and then recovers the former direction for a variable distance from half a mile to twelve miles, when similar changes of dip occur, with or without metalliferous indications. These linear alterations of dip, or axes, present two chief varieties, termed by the author, respectively," axes of change," and "axes of disturbance." Some of the axes appear to be branched. The surface of the metalliferous runs is much cross-fissured and decomposed; the rocks are stained of a bright green colour by silicate of copper, and lumps of oxide of copper are scattered on the surface, or in the fissures. When these are followed downwards, they often widen at first into largish veins, which at depths varying from 4 to 25 feet generally contract, sometimes terminating abruptly. At a greater depth purple sulphuret of copper occurs, and still lower copper-pyrites, either in fissures between masses of slightly decomposed granite, or diffused in grains throughout the granite. Dr. Rubidge described the relations of the Springbok, Koperberg, Concordia, Hoeklip, Rietburg, and other mines, to the several metalliferous axes, as far as his opportunities had enabled him to form an opinion; and then offered some remarks on the probable origin of the succession of the ores observed in the axes, several of the facts connected with them pointing, in his opinion, to the agency of water, and perhaps of magneto-electrical force as having produced many of the phænomena. The mines to the northward, near Henkries and Pella, present different conditions of the metalliferous rocks to those of Springbok and the southern mines. In the Orange River county, hornblendic, micaceous, and other schistose rocks are penetrated by granitic dykes and masses; and the copper-ores occur in small masses, disseminated through the crystalline veins, and sometimes in the rocks themselves. CAMBRIDGE PHILOSOPHICAL SOCIETY. [Continued from vol. xii. p. 403.] March 10, 1856.—A paper was read by L. Barrett, Esq., "On the Distribution of the Mollusca on the Coast of Norway." (Vide Annals of Nat. Hist. May 1856.) In this the author observed, that when the fauna of the coast of Norway is compared with that of the other side of the North Atlantic, a great difference will at once be perceived, not only in the number of species, but also in the different distribution of northern and southern types; the Mollusca of Greenland being peculiarly arctic, those of Scandinavia a mixture of southern and northern species. In the southern part of Norway we find the species living on our coasts abundant; but they become rarer as we go north, their place being supplied by arctic forms. Many of the northern species have a great geographical range, at which we need not be surprised when we consider their great antiquity, many of them having existed since the pliocene period; and, in the author's opinion, whenever we find a species with a great geographical range, we may at once infer that it has continued to live from a remote period. It is extremely difficult, according to the present state of the currents in the northern seas, to account for the wide distribution of arctic shells on this side of the North Atlantic; but when we consider that at not a very distant period the temperature and other conditions of this area were totally different, that a cold climate prevailed, certainly accompanied by a current setting from the north (as is fully proved by the fact that boulders are always found nearly south of the mountain ranges from which they have been originally transported), and that many of the shells are found fossil in the Sicilian tertiaries, this wide distribution may be fully accounted for. As these frigid conditions were gradually altering to more genial ones, those species requiring a lower temperature would gradually die out, and only continue to exist in higher latitudes. The littoral and shallow water species would be most affected by such an alteration of climate; and while the fauna of the littoral and laminarian zones would be entirely changed,-the shells composing that fauna replaced by other species, those living in the deep sea would continue to exist, perhaps at a greater depth, mingled with the species brought in with the new physical conditions of the area. This we know to be the case; for while the northern littoral shells, such as Mya truncata, &c., are found only fossil in Sicily, many of the deep-sea arctic species that existed there when those fossils were alive are still found living in the deeper parts of the Mediterranean. The same thing occurs on our coasts, where the arctic littoral or shallow-water shells, as Astarte arctica, Tellina proxima, Natica helicoides, &c., which are found in shallow water on the Scandinavian or Greenland coasts, are now rare as deep-sea shells, and that in the same area in which they were formerly abundant as shallowwater species. Some species are capable of enduring great differences of climate, the Mytilus edulis being found as abundantly on the coast of Greenland as on our own shores. It is not difficult to account for the presence of the southern species on the coast of Norway, as the Gulf-stream sets directly along the coast, warming its waters, and rendering them habitable for species requiring a moderately high temperature. The great abundance and wide distribution of these species show that the present order of things has continued for a great length of time. The gradual extinction of northern shells on our coasts is still going on; the number of living specimens of Pecten danicus is very small, while dead shells are very abundant, and fresh dead specimens of Pecten islandicus are frequently dredged, though a living specimen has not yet occurred. It is probable that this species has died out very recently. On the eastern shores of Davis's Straits the Mollusca are about half as numerous as on the coast of Norway. The fauna differs in the prevalence of arctic types and the total absence of southern. At a former period the fauna was of a mixed character; species now inhabiting more southern latitudes are found fossil in the raised beaches at Disco Island, which species are no longer found living on the coasts. Nov. 6.-A paper was read by Dr. Donaldson "On the Structure of the Athenian Trireme, considered with reference to certain difficulties of Interpretation." The author's intention was to show in this paper that the arrangements for seating the three tiers of rowers in the trireme, which Dr. Arnold has called "an indiscoverable problem," may be adequately explained by an examination of the terms which are used to discriminate the rowers, and of other words referring to the different parts of the war-galley. The name of the zygitæ, or rowers of the middle tier, implies that they sat on the Zvyá, or transverse planks connecting the opposite sides of the vessel, also called oéλuara, and in earlier times Anîdes. The thalamita, or rowers of the lowest tier, must, in accordance with their name, have had their seats attached to the ribs of the vessel in the Oáλapos, or hold. And the thranite, or rowers of the highest tier, sat on Opývves, or benches like low stools, extending for seven feet along the alternate vyά. The epibatæ, or marines, whether as working the supernumerary oars, or as fighting, occupied platforms running along the bulwarks. This view of the matter explained the fact that there was a gangway from the stern to the prow for the passage of the officers, &c. along the oλuara or (vyá, between the ends of the stools on which the thranitæ sat. This gangway was called the reλis, and the same name was given to the passages leading down to the orchestra from the upper part of the theatre between the rows of seats occupied by the spectators. Hence was derived a philological explanation of the words in Aristoph. Equites, 546: αἴρεσθ ̓ αὐτῷ πολὺ τὸ ῥόθιον, παραπέμψατ' ἐφ ̓ ἕνδεκα κώπαις for there were eleven tiers of seats between each diazoma of the theatre, which were divided again by the selis; so that the spectators would represent eleven banks of oars, seated, as in the trireme, with the lower rows in advance. In the same way, the use of the selis in a trireme, as the gangway for the officers, &c., explains the lines in the Agamemnon of Eschylus, 1588-9: σὺ ταῦτα φωνεῖς νερτέρᾳ προσήμενος κώπῃ, κρατούντων τῶν ἐπὶ ζυγῷ δορός ; for if the zygitæ had been intended, they must have been described as τῶν ἐπὶ ζυγών. The same view of the σέλματα, as the proper place for the officers, was used to explain another passage in the same play (v. 1413), where Agamemnon's companion is described as ναυτικών σελμάτων ἱστοτριβής. And the risk of passing along these planks, with intervals between them, was considered to explain the proverbial warning that we must take care not to miss our footing and fall into the hold (Eurip. Heracl. 168). Other points were incidentally noticed. Nov. 10.-The Master of Trinity read a paper "On the Platonic Theory of Ideas." In this, he first stated the Platonic theory of ideas as given by the late Professor Butler of Dublin, in his 'Lectures' (vol. ii. p.117); he then remarked that this theory had evidently, for one of its objects, to explain the possibility of necessary, and therefore eternal truths; and thus was an attempt to solve the problem, often debated in modern times, of the grounds of mathematical truth; an attempt especially called out by the Heraclitean skepticism of Plato's time. The doctrine of ideas which belong to the intelligible, not to the visible world, and which are the basis of demonstration, did really answer its purpose, and account for the existence of real and eternal truths; and at the same time, by the tenet that sensible things participate in those ideas, accounted for the securing of truth respecting the sensible world. But when Plato goes on to speak of ideas of tables and chairs and the like, he gives an extension of the theory which solves no difficulty, and for which no valid reason is rendered. The arguments against this extension of the theory are given with great force in the Dialogue entitled Parmenides, and are not answered there, nor in a satisfactory way, in any part of Plato's writings. Moreover, throughout this Dialogue, Parmenides is represented as having, in his conversation with Socrates, vastly the superiority, not only in argument, but in temper and manner; and Socrates and his friends, after a little show of resistance, assent submissively to all that Parmenides says. On this ground the writer maintains that the Dialogue is not Plato's, but anti-Platonic, written probably by an admirer of Parmenides, and tending to represent Socrates and his disciples as poor philosophers, conceited talkers, and feeble disputants. This view was further confirmed by arguments drawn from the external circumstances of the Dialogue. Nov. 24.-An account was given by Professor Miller, of the restoration of the Standard of Weight (vide Phil. Mag. vol. xii. p. 540, and p. 194 of the present volume. Phil. Mag. S. 4. Vol. 13. No. 85. March 1857. Q Dec. 8.-Mr. Humphry read a paper "On the relations of the Vertebrate Skeleton to the Nervous System." He pointed out that the central parts, both of the skeleton and of the nervous system, are composed of segments placed in front of, or above one another: those of the former being called "vertebræ," those of the latter "ganglia;" that the vertebræ correspond with the ganglia, each vertebra having its appropriate ganglion; and further, that the processes, or nerves, emanating from the central ganglionic portion of the nervous system correspond with, and accompany the processes, or bones, appended to the central portion of the skeleton, so that the bones appended to any particular vertebra are generally accompanied by the nerves emanating from the ganglion connected with that vertebra. Hence, where a difficulty is found in referring a bone to its vertebra, assistance may often be derived from a reference to the nerve or nerves which accompany that bone. Following the guide thus indicated, Mr. Humphry would refer the upper extremity, not to one-the occipital-vertebra, according to the plan of Professor Owen, but to several cervical vertebræ, forasmuch as it derives its nerves from a considerable tract of the cervical portion of the cord. For the like reason, the lower extremity may be regarded as appertaining to several lumbar and sacral vertebræ. The relations of the bones of the face to their respective cranial vertebrae were pointed out in accordance with the distribution of the cerebral nerves. It was shown, that although the size and shape of the skull are proportioned to the size and shape of the brain, yet that, as a general rule, the thickness and weight of the skull are in an inverse ratio to the size of the brain. A comparison of the different nations of mankind proves, moreover, that the size of the whole skeleton, as well as that of the skull, is usually proportioned to the size of the brain; a well-developed physique being the natural associate of an ample cerebrum. XXXI. Intelligence and Miscellaneous Articles. THE TELESCOPIC STEREOSCOPE. To the Editors of the Philosophical Magazine and Journal. GENTLEMEN, SINCE sending you the account of the stereoscopes proposed by myself and Mr. Waterston for uniting large binocular pictures, my attention has been called to a description, contained in Sir David Brewster's Treatise on the Stereoscope, of an instrument so nearly resembling what I have called the telescopic stereoscope, that, had it not entirely escaped my recollection, I would never have spoken of mine as new. The only difference, beyond unimportant details, is that the instrument described by Sir David Brewster appears to have been intended only for small pictures near at hand, while mine was designed to unite large pictures viewed at a distance. The latter object alone being that which I had in view, and recollecting no description of any instrument for that purpose in Sir David's work, it did not occur to me to search the volume again before sending you my account, although I endeavoured in every other way to ascertain if such a |