in its dissimilar molars, the types of two genera: the molars of its upper jaw represent those of both jaws of Ctenomys; those of its lower jaw correspond with the molars of both jaws of Poephagomys. The characters distinguishing the new species of Ctenomys are chiefly those of colour. The Cten. Brasiliensis is described by M. de Blainville as being shining rufous above, and reddish white below. The new species may be characterized as the Ctenomys Magellanicus. Captain King states that this "little animal is very timid; feeds upon grass; and is eaten by the Patagonian Indians. It inhabits holes, which it burrows, in the ground: and, from the number of the holes, it would appear to be very abundant." A second animal exhibited appears, like the preceding, to represent in the more southern latitudes of South America a genus whose type was originally observed in Brasil. Mr. Bennett regarded it as a second species of Kerodon, F. Cuv., chiefly distinguishable from the one discovered by Prince Maximilian of Wied by its more uniform colour. Excepting a slight dash of white behind the ear, and a longer line of the same colour marking the edge of each branch of the lower jaw, the animal is entirely grey; the upper surface being distinguished from the under by a greater depth of tint, and by the intermixture of a free grizzling of yellow and black. The crowns of the molar teeth, as in the typical species, consist of bone surrounded by two triangles of enamel, the bases of which are connected together by a short line of enamel passing from the one to the other: all the lines being slender and sharply defined. For this species Mr. Bennett proposed the name of Kerodon Kingii. The third animal exhibited was remarked on as constituting a new species of Cavy, distinct from all those that were previously known, including the two which have recently been described by M. Brandt in the Nouveaux Mémoires de l'Académie Impériale de St. Petersbourg.' Mr. Bennett characterized it as the Cavia Cutleri, King MSS. The general form of the animal is probably similar to that of the restless Cavy, Cavia Cobaya, Gmel., popularly known as the Guineapig. It is covered universally by long, smooth, glossy, black hairs, which are slightly tinged with brown. Its ears are rather large, broadly expanded, and hairy; and between them the hairs are longer than those on the adjoining parts, occasioning a slight appearance of a crest. On the middle of each cheek the hairs radiate as from a centre, almost in a similar manner to that in which they spread from around the crown of the bonneted Monkeys, and the skin is consequently left in the middle point almost bare. The dentition is altogether that of the restless Cavy, and the incisors, as in it, are white. The skull is rather more expanded laterally, which gives to it an appearance of comparative flatness. "This animal was known, on the survey, by the name of the Peruvian Cavy. The specimen in the Society's collection was presented to one of the officers of the Beagle by an American sailing-master, of Stonington, U.S., a very intelligent person, to whom we were much indebted. The trivial name which I have proposed for it is in recollection of the benefit we derived from his experience and knowledge of the intricate navigation of the south-western coast of Patagonia, which was freely imparted to us on several occasions.". P. P. K. The collection also contained specimens of a Mouse, for which Mr. Bennett proposed the name of Mus Magellanicus. Specimens were exhibited of several Marsupialia, on which Mr. Ogilby made the following remarks. "A small collection of Marsupial Quadrupeds, which Mr. Gould lately received from his brother-in-law, Mr. Coxen, contains two or three interesting species, which the usual kindness of Mr. Gould enables me to notice. They were all procured, as I am informed, in the country beyond the Hunter River, about eighty miles north of Sydney in New South Wales. The most remarkable is an undescribed species of Phalanger, which I propose to call Phalangista Canina. It is similar in size and general proportions to Phal. Vulpina, and the two allied species described in the Proceedings' for 1830-31, page 135, (Phil. Mag. and Annals, N.S., vol. xi. p. 133.) but is easily distinguished from them all by the small size and round form of the ears, as well as by the distribution of the colours. All the upper parts of the body, the head, cheeks, back, sides, and outer face of the arms and thighs are of a uniform grizzled brown; the throat, breast, belly, and interior of the members dirty ashy grey with a slight shade of yellow. The ears are only an inch in length and about the same in breadth, being thus little more than half as long as in Phal. Vulpina. They are naked within, but covered with deep coffee-coloured fur on the outside; the nose, and the paws, both before and behind, are dark brown; and the tail is bushy and entirely black to within about 2 inches of its root, which is of the same colour as the back. All these circumstances distinguish the present species from Phal. Vulpina, with which alone it can possibly be confounded, and in which the backs of the ears, and the cheeks and paws are yellowish white, whilst the black colour occupies only the latter half of the tail. Both these animals have long black vibrissæ, and a tuft of similar stiff hair on the cheek, about an inch below and behind the eye. The whole length from the nose to the root of the tail is 2 feet; the length of the tail 134 inches. Phal. Cookii. I notice this species merely to observe that the present specimen is the only certain evidence we possess of this animal being an inhabitant of Continental Australia. Cook observed it in Van Diemen's Land, and I had never been able to ascertain the precise locality from which the various other individuals I had formerly examined, were obtained. Macropus Eugenii. This specimen agrees with M. Desmarest's description, and is interesting as coming from a very distant part of the country. Perameles obesula. An adult specimen of the same size as the full-grown Per. nasuta. I notice it to mention that the teeth are, in all respects, similar to those of Per. nasuta, both in form and number. The collection contains besides, two very fine specimens of Petaurus Taguanoides; one of Pet. Sciureus; one of Hydromys chrysogaster; and a young Koala."-W. O. PROCEEDINGS AT THE FRIDAY EVENING MEETINGS OF THE MEMBERS OF THE KOYAL INSTITUTION. March 25.-Mr. Goadby on Insect Anatomy. April 15.-Sir James South on Astronomical Observations as carried on in the fixed Observatory. April 22.-Sir James South. The same (concluded). May 6.-Mr. Daniell on a new and constant Voltaic Battery. May 13.-Dr. Lardner on Steam communication with India (concluded). May 20.-Professor Mayo on some of the uses of Sensation. June 3.-Mr. Beamish on the present state and prospects of the Thames Tunnel. Jnne 10.-Mr. Faraday. Considerations respecting the nature of Chemical Elements. CAMBRIDGE PHILOSOPHICAL SOCIETY. [Continued from vol. viii. p. 431.] A meeting of the Philosophical Society was held on Monday evening, April 18th, Dr. Clark, the President, in the chair. The Astronomer Royal (lately Prof. Airy) read a communication on the intensity of light in the neighbourhood of a caustic. One object of this investigation was to determine what must be the circumstances of the rainbow on the undulatory theory of light. Afterwards Mr. Hopkins gave an account of the agreement between the results of his theory of elevatory geological forces, and the phanomena of faults, as observed by him in the strata of Derbyshire. A meeting of this Society was held on Monday evening, May 2nd, Dr. Thackeray, Vice-President, in the chair. A memoir was read by S. Earnshaw, Esq., St. John's, "On the Integration of the Equation of Continuity of Fluids in Motion;" also a memoir by Professor Miller on the Measurements of the Axes of Optical Elasticity of certain Crystals. This memoir contained various determinations, from which it appears that the law concerning the connexion of the crystalline and the optical properties of crystals suggested by Professor Neumann, namely, that the optical axes are the axes of crystalline simplicity, is false; but that it is true, in many of the cases hitherto examined, that one of the optical axes coincides with the axis of a principal crystalline zone. Afterwards Mr.Webster, of Trinity College, made some observations on the periodical and occa sional changes of the height of the barometer, and on their connexion with the changes of temperature arising from the seasons and from the condensation of aqueous vapour. A meeting of this Society was 'also held on Monday evening, May 16th, Dr. Thackeray, V.P., in the chair. A letter from A. De Morgan, Esq., to the Rev. George Peacock, was read, containing a sketch of a method of introducing discontinuous constants into the arithmetical expressions for infinite series. Also a memoir by P. Kelland, Esq., of Queen's College, on the mathematical results of a mixture of elastic fluids (as air and vapour in the atmosphere), and on the theory of heat. With regard to the latter subject, the object was to show that there is a translation backwards or forwards of the calorific particles, consequent on and varying in intensity with the transverse vibration. Mr. Hopkins made some statements respecting experiments recently made on the temperature of mines and the doctrine of central heat. Mr. Airy gave an account of observations of temperature made during the great solar eclipse of May 15th. XV. Intelligence and Miscellaneous Articles. ON THE FEEBLE ATTRACTION OF THE ELECTRO-MAGNET FOR SMALL PARTICLES OF IRON AT SHORT DISTANCES. To the Editors of the Philosophical Magazine and Journal. GENTLEMEN, THE its HE enormous sustaining power of the electro-magnet has for some time been exhibited as a matter of great curiosity, but very feeble attraction for small particles of iron at short distances is not, I believe, very generally known. This fact was first mentioned to me by Mr. Clarkę, magnetical instrument-maker, which since then I have frequently noticed myself. I am not aware that any explanation of this seeming anomaly has as yet been given; I have therefore ventured to offer one, which, if considered satisfactory, and of interest sufficient to deserve a place in your valuable Journal, I shall be obliged by its insertion. It will be necessary first to observe the phænomena which take place when a piece of soft iron is under the influence of the ordinary horseshoe magnet. When the armature s'n' is brought near to the magnet NS, magnetism is induced in s'n'; and according to the law of magnetic induction each extremity of s'n' has its state of polarity opposite to that of the adjacent pole of the magnet NS, and a tendency to approach each other immediately takes place, and if the force of attraction be sufficient to overcome the inertia of s'n', contact will instantly follow. n S n' If the armature be sufficiently massive to receive all the mag netism N S is capable of inducing, the magnet will not be able to sustain any more, and consequently a limit to its inducing power must exist. The reaction of the armature upon the magnet will also strengthen the adhesion between them: probably the effect of this reaction will be influenced by the facility with which magnetism permeates the steel of which the magnet is made, and be greater in the softer kinds of steel. If this view be correct, the sustaining power of a common magnet cannot be considered as an exact measure of its magnetic intensity. When a piece of soft iron is placed at a short distance from the poles of an electro-magnet, under the influence of a galvanic current, a comparatively trivial effect is produced, showing that the magnet thus induced is but of feeble magnetic intensity. This is owing, probably, to the facility with which soft iron is permeated by magnetism, and consequently any considerable accumulation prevented. But when the iron is in contact with the poles of the electro-magnet, the magnetism, instead of escaping, will induce in the armature polarity, and the armature reacting powerfully on the soft iron of the electro-magnet, and receiving continuous additions of magnetism from the galvanic current, will be attracted by the magnet with increasing force until the attraction between them becomes immense. If the galvanic action be discontinued, the keeper will remain applied to the electro-magnet, though less firmly; and after it has been removed nearly all the magnetism escapes. If this explanation be correct, it will be obvious that the electromagnet will not be well adapted for the construction of magnetoelectrical machines, in which the armature is made to rotate rapidly in front of the poles of the magnet without actual contact. I am, &c. No. 1, Maze Pond, Borough, May 7, 1836. GEORGE RAINEY. OBSERVATIONS ON THE SOLAR ECLIPSE OF MAY 15, 1836; AND ON THE AURORA BOREALIS OF APRIL 22. To the Editors of the Philosophical Magazine and Journal of Science. GENTLEMEN, I am well aware that you must have received various accounts of observations made during the late eclipse; nevertheless, I beg to trouble you with one or two made by myself at that time upon the possibility of seeing the lunar mountains on the round or unbroken side of the moon, although it may be presumed that an account of the singular appearance at the time of the annular phase has been transmitted to you. I saw the roughness of the moon's edge from the beginning of the eclipse; but at the time of the ring becoming nearly equal on the eastern and western sides its narrowest part was divided directly across in two places, the light of the sun passing between the mountains. This affords an excellent method of calculating the heights of the lunar mountains; for it may be readily |
