The Mackenzie River, or, as Dr. Richardson has preferred naming it, the Hare-Indian Dog, is of small size and slender make. Its muzzle is narrow, elongated, and pointed; its ears broad at the base, pointed at the tip, and perfectly erect; its legs rather long and delicate; and its tail thick, bushy, and curved slightly upwards, but not by any means with the decided curl of the Esquimaux. Its body is covered with long straight hairs, the ground-colour of which is white, marked with large irregular patches of grayish black intermingled with various shades of brown. The ears are covered on the outside with short brown hair, which becomes blackish towards the margin and at the base; that of the inside is longer and white. On the muzzle the hair is white and very short, as also on the legs, but becomes thicker and somewhat longer on the feet, and is continued to, the very extremities of the toes. Dr. Richardson suspects that this variety of the Dog "was perhaps formerly generally spread over the northern parts of America; but being fitted only for the chase, it has, since the introduction of guns, gradually given way to the mongrel race sprung from the Esquimaux, Newfoundland and this very breed, with occasional intermixture of European kinds." It seems at present to be peculiar to the Hare-Indians and other tribes frequenting the banks of the Mackenzie River and Great Bear Lake, in the neighbourhood of which our enterprising countrymen, Captain Sir John Franklin and Dr. Richardson, wintered with their party, previously to setting forth on their late hazardous but eminently successful expedition to explore the northern coasts of the American continent. A pair of these graceful and elegant animals were brought away by the travellers on their return, and presented to the Zoological Society soon after their arrival in England, where the third was whelped. These, we believe, are the only individuals of the race that have ever been seen in Europe. Their air of frank and unsuspecting confidence is combined with an unusual share of gentleness and good temper. They seem perfectly at their ease, and soon become familiar even with strangers. In their native country they are never known to bark, and this peculiarity is still retained by the elder dogs; but the younger one, which was born in this country, has learned to imitate the language of its fellows. They appear to be extremely valuable to the Indians by whom they are bred, who subsist almost entirely on the produce of the chase. "The Hare-Indian Dog," says Dr. Richardson, "has neither courage nor strength to fit it for pulling THE WHITE-CHEEKED MARTEN. Mustela Flavigula. Bodd. Inferiour in predatory character to the Cats alone, to which they bear a close resemblance in many points of their organization, the Weasels constitute one of the most strongly marked families among the Carnivora. In slenderness of form, sleekness of fur, and agility of motion, they are excelled by none. Their long narrow cylindrical bodies are supported by short muscular legs, which are usually bent beneath them in such a manner that their bellies appear almost to glide along the ground; while the head and neck, the latter of which is unusually elongated, are of nearly equal diameter with the rest of the body. The upper and anteriour part of their heads is flattened and has a somewhat triangular form; their ears are small and rounded; their eyes of moderate size, with round or transversely elongated pupils; their nostrils seated at the extremity of a moist glandular muzzle; their tongues clothed with raised sharp horny papillæ; and their toes, of which there are five to each foot, armed with long, slender, sharp, curved, semiretractile claws. These claws. although sharp at the points, want the cutting edges possessed by the same organs in the Cats, and are besides but ill calculated by their want of strength for seizing on their prey. They are also incapacitated by the latter circumstance for burrowing in the earth, like those of the Dogs and Bears; and they seem rather to be of use in climbing trees, a feat which these animals execute with great dexterity, travelling among the branches with such rapidity as to seem rather to fly than to run. They usually remain during the greater part of the day asleep in their retreats, but towards night they begin to rouse themselves and prowl abroad in search of the living victims on which they chiefly feed. In uninhabited districts these are commonly found among the smaller animals of the Rodent Order; but a still more plentiful supply is frequently derived in cultivated countries from the farm-yard, in which the poultry forms the principal object of their nocturnal incursions. Their visits are sometimes attended with the most extensive devastation, their sanguinary dispositions impelling them to the commission of wholesale destruction for the gratification of their excessive thirst of blood. In the more typical groups of the family, constituting the major part of the Linnæan genus Mustela, the dentition is nearly uniform, and consists most commonly of six incisors and two canines in each jaw; of two false molars, one lacerator, and one tubercular tooth in the upper jaw, and of three false molars, a lacerator, and a tubercular tooth in the lower. The group, however, for which M. Cuvier has retained the generick name of Mustela, are distinguished from the rest by being furnished with an additional rudimentary false molar in either jaw. Their muzzles are consequently somewhat more lengthened than those of the other divisions. They have also a small tubercle on the inner side of the lower lacerator; and these two characters indicate a trifling diminution in their carnivorous propensities. Their walk is digitigra le, but less completely so than in the Dogs and Cats; and their fur is, generally speaking, remarkable for its length, its fineness, and its gloss. The fine species which forms the subject of the present article is the largest of the group. It is an animal of extreme rarity, having been well described and figured for the first time by Dr. Horsfield, in the Zoological Journal, about six years ago, under the name of Mustela Hardwickii, from a skin presented by General Hardwicke to the Museum of the East India Company. It had, however, escaped the researches of that excellent zoologist that the living animal had been seen by Pennant so long ago as the year 1774, and was described by him in the first edition of his History of Quadrupeds, published in 1781, briefly indeed, but in terms sufficiently precise not to be mistaken. From this description of Pennant, the only writer previous to Dr. Horsfield who appears to have had any personal knowledge of the animal, it was adopted into the compilations of Boddært and Shaw; the former of whom gave it the appellation of Mustela flavigula, and the latter designated it as the Viverra quadricolor. It seems to have been either passed over, or regarded as doubtful, by all the other compilers of general lists of the Mammalia. It is a native of India. ears both within and without, and a patch surrounding each of the eyes, are of a dusky black. Notwithstanding the apparent capacity of their cranium, the dogs of this tribe are by no means remarkable for their intelligence. They are, however, eminently faithful, and as courageous as they are powerful. They are consequently chosen in preference to all others for house-guards and watch dogs, and are also in much request, wherever such sports are encouraged, for bull fights and other similar exhibitions of brutality, For their legitimate purposes they are a most useful race. CHYMISTRY. ON SOLUTION. It is about two feet in length, with a tail of nearly equal dimensions. The head, nose, and upper lip, the sides of the face including the ears, the back of the Solution is the result of an affinity between neck, the tail and adjacent parts of the body, and the bodies in different states with regard to cohesion. In limbs, both within and without, are of a deep shining this case liquids are called solvents; and they can act black. The chin and lower jaw are pure white, and upon, or hold in solution, either solids or aeriform fluids. the throat is of a bright yellow, blending on the sides We have already alluded to instances of the solution with the brown of the back, the whole of the upper and of solids as illustrations of the general subject of affinfore parts of which, together with the belly, are uni-ity; and we have shown that the power of cohesion is formly of the latter colour, except on the shoulders opposed to this action. Between some liquids and where the hairs are tipped with yellow. The tail is solids there appears to be no attraction whatever; or, perfectly cylindrical and clothed with long and some- if any, it is inferiour to the attraction of cohesion by what rigid hairs. The pupils are round; the ears short; which, the homogeneous particles of the solids are the whiskers moderately long; the palms of the fore united; thus rosin is wholly insoluble in water, but feet large and of a dusky colour; and the claws of all readily unites with alcohol. nearly white. THE CUBAN MASTIFF. Canis Familiaris. Var. And here we may remark, that chymical attraction, in general, may be exerted in different degrees between one body and several others. There is, as we have seen, a mutual affinity between alcohol and water, whereby they are capable of mixing; there is also a This fine pair of Dogs which were presented to the mutual affinity between alcohol and rosin, whereby London Zoological Society by Captain Marryatt, the former is capable of dissolving the latter; and who obtained them from Cuba, partake of the char- there is no affinity between water and rosin. Now if, acters of the Spanish Bull-dog and English Mastiff, to a solution of rosin in alcohol, water be added, it will and seem to be completely intermediate in form be- be found that the rosin will resume the solid form: tween the two. They are larger than our common the attraction between the particles of alcohol and Bull-dogs and smaller than the Mastiff, well made and rather stout in their proportions, moderately high upon their legs, muscular and powerful. Their muzzle is short, broad, and abruptly truncate at the extremity, with somewhat of an upward curve; the head broad and flat, and the lips elongated and so deeply pendulous as to overlap the margins of the lower jaw. The ears, which are of a middling size, are also partly pendulous, but not to such an extent as to lie flat upon the sides of the head. The tail is rather short. cylindrical, and turned upwards and forwards towards the tip. Their hair is throughout short, close, and even. On the upper parts it is of a bright brown, becoming somewhat paler beneath. The muzzle, lips, those of water, is greater than between the particles of alcohol and those of rosin; the consequence is, that the alcohol quits the rosin, and combines with the water, and the attraction of cohesion being no longer opposed, resumes its ascendancy. This has been called elective attraction, because the alcohol may figuratively be said to exercise a choice between the substances with which it is capable of combining. This resumption of the solid form of a substance, previously dissolved in a liquid, is termed precipitation; although the term can only be strictly applied where the solid, set at liberty, falls to the bottom of the vessel. Unlike the case of mixture, there is a limit to the power of solution; and liquids cannot combine with more than a certain definite quantity of any solid or aeriform body: thus water will only take up a certain known weight of alum, or alcohol of rosin. The point at which the action between the two bodies ceases, is called the point of saturation. Up to this point the two bodies may combine in any proportions. Carbonick acid, or that aeriform substance, formerly known by the name of fixed air, which most persons are acquainted with, as given off from bottled beer or soda water, is capable of being absorbed by water; which liquid, under ordinary circumstances, will take up rather more than its own bulk of this air (or gas.) As in the case of solids, the attractive power of cohesion, at a certain point, balances the action of the solvent, so, in aeriform bodies, the repulsive power of elasticity sets similar limits to its exertion. It is only to a certain point that the solvent power of water can counteract the elasticity of the carbonick acid; and beyond this point of saturation it cannot unite with it. The influence of heat upon the power of solution, corresponds with the difference between cohesion and elasticity. Upon solid bodies it generally increases the power of the solvent, by diminishing their cohesion. Upon aeriform bodies it diminishes the power, by adding to their elasticity. Water may be saturated with alum at the common temperature of the atmosphere, and if heat be afterwards applied, will dissolve an additional quantity; if the solution be then allowed to cool, the attraction of cohesion will resume its ascendancy, and the second portion of the alum will be deposited in solid and regular forms. If, on the contrary, a saturated solution of carbonick acid in water be heated, the gas will escape from its combination; for the heat increases the repulsive power of the particles of the gas, and the affinity of the solvent is no longer able to counteract it. A solvent that has been saturated with one substance, is often capable of combining at the same time with others; thus water which has taken up its full proportion of salt petre, will further dissolve a considerable quantity of common salt. The process of the solution of a solid in a liquid, is very frequently accompanied by a diminution of temperature; and great degrees of cold may be produced by dissolving certain proportions of different salts in water. A reduction of 170 is produced, by merely saturating water at common temperatures with nitre; and nitrate of ammonia will, in the same way, lower the thermometer from 50° to 4°. The solution of gases, on the contrary, is generally accompanied by the production of heat. The properties of bodies are not changed by solution any more than by mixture; and the characters of such combinations are intermediate between those of their ingredients. The most universal solvent in nature is water; and as the characters of that liquid are very neutral, i. e. distinguished by no very energetick or active properties, aqueous solutions, in general, possess in an eminent degree the properties of the solids or gases with which they are combined. cohesion, as well as the repulsive power of elasticity, are in various degrees opposed even to this power; and till reduced or modified, often prevent its action altogether. The state of liquidity is consequently most favourable to its efficiency. The union of bodies in this intimate manner only takes place in definite proportions, which are invaria ble in the same compound, and 1 is commonly accompanied by a total change of their sensible properties. Great alterations of temperature almost always accompany the act of combination; and when the action is most energetick, light and heat are given off in abundance, and often with violence. If copper filings and sulphur be mechanically mixed together, they will exhibit no tendency to unite at the common temperature of the atmosphere; but if heat be applied, as soon as the latter melts, a violent action will take place; the copper will become red hot, and a black, brittle body will be produced, with properties totally different from those of its two ingredients. This compound is often found ready formed in mineral veins; but whether the product of nature or of art, as above described, its composition is definite and invariable; and it is found to consist of sixty-four parts of copper to sixteen parts of sulphur: or 100 parts contain eighty copper and twenty sulphur. Our reason for preferring the statement of the proportion in the former numbers will hereafter appear. It often happens, however, that a body will unite in this manner in more than one proportion with another; the composition in each case being no less definite and fixed: but the proportion of one of the ingredients of the resulting compound is always some multiple or sub-multiple of that in the first compound; that is to say, it is double or treble, or half, and so on. Thus a second combination of copper and sulphur is known, which, although it cannot be produced by the direct union of the two bodies, is of very common occurrence, and constitutes the important ore from which nearly all the copper of commerce is derived. The proportions of this compound are sixty-four copper to thirty-two sulphur; that is to say, the copper is combined with exactly double the proportion of sulphur which exists in the first combination. The compounds which mercury or quicksilver forms with some other bodies, are well calculated to exhibit the striking difference of character which are the results, not only of chymical composition, but of composition in different proportions. If this brilliant, white, fluia metal be agitated for a long time in contact with the common air, it will unite with the oxygen of that mixture, and will be converted into a black, insipid, insoluble powder; which consists of 200 parts of mercury to eight of oxygen. If, instead of being agitated at common temperatures with the air, it be kept heated with it to nearly its boiling point, it will be converted into a red, shining mass, also a compound of the metal and oxygen; but which is endued with an acrid, metallick taste, is soluble in water, and poisonous. It consists of 200 parts of mercury, and sixteen of oxygen. Mercury also combines with sulphur in two proportions: by long-continued trituration (or rubbing in a mortar) the two bodies unite, and form a black, tasteless compound, which contains 200 parts of mercury to Solvents may be separated from the bodies with which they are united by alterations of temperature, which change their state of cohesion. If a solution of alum be strongly heated, or boiled, the liquid will assume the state of vapour, or of an elastick fluid, and flying off, the solid will remain. If a solution of car-sixteen of sulphur. bonick acid in water be frozen, the gas will escape, and the water remain in the solid state. The affinities, however, of some gases for water are so strong, that they rise in union with its vapour, and cannot be separated by evaporation. CHYMICAL COMPOSITION. Composition is the result of the highest degree of chymical attraction; which may take effect between bodies whose particles are under every modification of cohesive attraction. The attractive force, however, of If mercury be poured into melted sulphur, and strongly heated, a compound will be formed, which rises in vapour, and concretes, on cooling, into a brilliant red substance, known by the name of cinnabar or vermillion. It is composed of 200 parts of mercury, and thirtytwo of sulphur. Again, the well-known medicine called calomel, is a compound of mercury, and an aeriform substance, which we shall hereafter describe, called chlorine. This, compound is white, crystalline, very heavy, tasteless, and nearly insoluble in water. It may be 392 taken in doses of several grains without any effect, but | new adjustment of the various affinities: that is to say, Mercury is capable of combining with a further portion of the same gaseous body; in which case it is proconverted into a semitransparent, white mass, of an acrid, nauseous, metallick taste, soluble in water and alcohol, and highly poisonous. It is well known by the name of corrosive sublimate, and is composed of 200 parts of mercury, and seventy-two parts of chlorine. Thus substances, comparatively inert, may produce, by their union, compounds of highly active properties; and a compound of two bodies, which, in one fixed proportion will, if taken internally, have but a slight effect upon the animal frame, if united in a different proportion, will prove destructive to life. Highly active bodies of opposite properties will also produce by their combination substances of mild character, and they are then said to neutralize each other. Sulphurick acid, or oil of vitriol, to which we have before referred as a well-known liquid, for the purpose of illustrating the nature of chymical mixture is highly corrosive, and possesses an intensely sour taste. If brought into contact with a substance stained with the delicate colour of any blue vegetable, such as that of violets or litmus, it instantly changes its tint to bright red; a property which belongs to all acids. There is another substance, also well known, and commonly to be met with, called Barilla, or carbonate of soda. It is a solid, soluble in water, of a hot, acrid, bitter tase. It changes the blue colour of vegetables to green; a property which belongs to a class of bodies denominated alkalies. Between these two bodies a strong affinity subsists. If into a solution of the latter we carefully drop a portion of the former, a brisk effervescence will ensue, and carbonick acid, or fixed air, will be given off, as from soda water. If the experiment be performed with care, and the dropping in of the acid stopped, the moment the effervescence ceases, the solution will be found to be warm, and to be possessed of properties totally different from those of the acid and the alkali from which it has been formed. It will not be sour, corrosive, acrid, nor hot. It will have no action upon blue vegetable colours, and all the active properties of the original bodies are said to be neutralized--they have neutralized one another. The product is slightly bitter, saline, and cooling. If part of the water be driven off by heat (or evaporated,) a solid will be deposited in regular forms, which was previously held in solution by the water which escapes. This substance is known by name of Glauber's salt, or sulphate of soda, and is extensively used in medicine. That power of affinity which produces chymical composition may, as in the case of solution, exist in a body in different degrees towards other bodies; and if to a compound of two bodies a third be presented which has a stronger attraction for either of the two ingredients than they have for each other, decomposition of the original compound will take place, and a new compound will result. Barilla, or carbonate of soda, to which we have just referred, is a compound of a highly caustick, alkaline substance, called soda and carbonick acid. In the experiment above alluded to, it is decomposed; the sulphurick acid expels the carbonick acid, which escapes in effervescence, and takes its place with the soda. If a solution of this substance in water be boiled with caustick lime, the carbonate of soda will be decomposed, the carbonick acid will quit the soda and unite with the lime and carbonate of lime, or chalk, and caustick soda will be the result. This action is called, for the reason already explained, single elective affinity. If two compounds be brought together in solution, it will not unfrequently happen that a process of double decomposition and composition will take place from a The substance known by the name of sugar of lead, White vitriol is composed of sulphurick acid and zinc. is a compound of vinegar, or acetick acid and lead. Now if, in a solution of the former substance in water, we suspend a piece of metallick zinc, we shall have an example of single elective affinity. The attraction of therefore abandon the lead, which will resume its vinegar for zinc is greater than for lead; the acid will metallick form, and unite with the zinc. The experiment is very beautiful as the lead is precipitated upon the zinc in an arborescent form. But if a solution of acetate of lead be mixed with a solution of sulphate of to unite with the zinc; but at the same moment, the zinc, the acetick acid will, as before, abandon the lead, sulphurick acid will attract the lead, and form with it an insoluble compound, which will be precipitated in action has been distinguished by the name of double the form of a heavy white powder. This compound elective affinity. effected by single elective affinity may often be produDecompositions which cannot be ced by double elective affinity. acetick acid which originally was combined with the Now we may remark, that the same quantity of lead, is exactly sufficient to enter into combination with acid which entered into composition with the zinc, the zinc; and also that the same quantity of sulphurick exactly suffices for the lead: none of the ingredients are found in excess, and the proportions of each are equivalent to each other in their power of combining. This observation exemplifies another fundamental law of chymical composition; namely, that bodies not only combine together in proportions which are fixed with regard to each other, in any given compound, but are also definite with regard to every other substance with which they are capable of entering into composition; so that there are certain determinate proportions of all bodies which are equivalent to each other in their powers of combining with all other bodies. Thus sugar of lead, or acetate of lead, is a compound of fifty parts of acetick acid and 112 parts of lead in the state (which will be hereafter explained) of an oxyde. White vitriol, or sulphate of zinc, is composed of forty parts of sulphurick acid, and forty-one parts of zinc, also in the state of oxyde. Now these proportions are all equivalent to one another; and if we write their numbers against the different substances as follows, will unite in any new combination. we can at once perceive the proportions in which they Sulphurick acid 40 41 50 112 double decomposition above referred to, that the white Thus, from such a table we may anticipate, in the powder or new compound of sulphurick acid, and lead, precipitated, must consist of forty parts of the former and 112 of the latter; and likewise that the combination of zinc and acetick acid, left in solution, must be in the proportion of fifty parts of acid and forty-one parts of zinc: and this exactly agrees with the results of experiment. lent numbers, or their multiples, are preserved in every We shall hereafter find that the same equivapossible combination with other bodies; and that similar numbers may be attached to all the known substances of the chymical catalogue. Moreover, when any body is compounded of two simple substances and enters into combination with another body, the sum of the equivalents of the two elements will give the numHaving endeavoured to convey a general idea of this ber, denoting the proportion in which it will so combine. universal law of chymical composition, it does not enter into our plan to pursue the subject further in this The attraction of cohesion is opposed to the highest degree of chymical attraction in the same way as to the inferiour degrees. Barilla or carbonate of soda is capable of acting strongly upon pounded flint, and produces, by its combination with it, the well-known substance, crown-glass: but before the attraction of cohesion in the flint is diminished by pounding, the chymical affinity between them is not efficient. place: its full developement will only be found in the | of the globe and its parts. These representations emcomplete body of chymical facts. brace either the whole earth, or a part of the world, or a single country. In the first case they are called maps of the world, and when they have a circular form, hemispheres; those of the second class are called general maps; the others are special maps. Among the special maps, some represent a province on a large scale, with all its remarkable places; these are chorographick maps. If the designer has entered into all the details of the nature of the ground, or has even traced out insulated habitations, and the direction of roads and rivers, they are topographical maps. Geographical maps, properly so called, are also distinguished from those that are appropriated to a particular use; such are hydrographick charts, destined for mariners, mineralogical maps, and others. The minor degree of affinity by which solution is effected has also a strong influence over the power of composition. It acts chiefly by counteracting cohesion and repulsion, and thus bringing the particles of solids and aeriform fluids within the sphere of mutual action. Sugar of lead and white vitriol, in their solid forms, have no action upon each other; but balance their powers of cohesion by dissolving them in water, and the double elective affinity is immediately at liberty to act in the way which we have pointed out. There is another circumstance, mechanical in its The figure of the earth, prevents the possibility of nature, and the influence of which is somewhat obscure, giving a general picture in which the distances of which sometimes interferes with chymical composi-places, and the relative extent of regions, might be pretion; that is, quantity: for, in comparing the attraction of two bodies for a third, a weaker affinity in one of the two is found to be compensated by increasing its quantity. If one part of common salt (which may be considered as composed of muriatick acid and soda) be mechanically mixed with half its weight of red lead (oxyde of lead) and water, to the consistency of a thin paste, no decomposition of the salt will ensue: the soda has a stronger attraction for the acid than the oxyde of lead. If, however, the weight of the red lead be increased to three or four times that of the salt, after standing some time, the strong taste of the soda will be perceptible; proving that the larger quantity of the oxyde has the power of detaching a considerable portion of muriatick acid from the soda, notwithstanding the stronger affinity. served in their mutual relations. There are curved surfaces, which can be extended on a plane without rent or duplication, and which for this reason are called developable surfaces; such are those of cones and cylinders: but others like those of the sphere and spheroids, cannot be so extended. The earth being a spheroid, its surface cannot coincide rigorously with a plane; and thence results the impossibility of making on a map at the same time, and in their natural relations, the extent of countries, the distances of places and the simiade of configurations. Geographers are obliged to have recourse to various constructions, to represent at least in an approximate manner, each of these relations in particular. The influence of temperature upon the highest degree of chymical attraction, is various: sometimes it These constructions have received the name of favours its operation by counteracting the cohesion of solids; sometimes it opposes it by increasing the re-projections; a name applied in general to designs, the pulsion of aeriform fluids. An increase of heat fre- object of which is to indicate on a plane the dimensions quently increases directly the energy of affinity, and of space, and of the bodies it contains. They are of determines combinations which would not otherwise take effect; and different degrees of temperature often produce opposite effects. We have shown that, by raising the temperature of quicksilver or mercury to nearly its boiling point, a combination is determined between it and oxygen, one of the mixed gases of the atmosphere: if this compound be more strongly heated still, it will be decomposed, and oxygen and the metal will be reproduced. If a spirit lamp be supplied with ether instead of alcohol, it will inflame upon approaching to it a body in a state of inflammation; but if instead of a body of so high a degree of heat, a coil of platina wire, heated to redness, be laid upon the wick, the ether will still be consumed, and the wire will continue to glow, but no flame will be produced. The products of these two species of combustion will be totally different, and each is determined by the degree of temperature at first communicated, and which is maintained without variation, by the heat evolved in each process. Chymistry will be continued in the third volume, commencing with Chymical Decomposition. MATHEMATICAL GEOGRAPHY. GEOGRAPHICAL MAPS. two kinds: some are real perspectives of the globe, or of parts of its surface, taken from different points of view, and on different planes; the others are only a kind of developements, subject to approximating laws, and appropriated to the relations which it is wished to preserve in preference. Projection, signifies the representation of an object on the perspective plane, or, it is the pictorial delineation of an object on a plain or flat surface. Orthographick projection is that where the surface of the sphere is represented by a plane which cuts it through the middle, the eye being placed vertically at an infinite distance from the two hemispheres. It will be observed, that the rays by which the eye sees at an infinite distance are parallel. Stereographiek projection is that where the surface of the sphere is represented on the plane of one of its great circles, the eye being supposed at the pole of that circle. In the stereographick projection the globe is considered as a transparent solid. The hemisphere represented is that which is opposed to the hemisphere in which the eye is supposed to be. Besides the orthographick an 'stereographick projection, there is a third projection in perspective called central. It is obtained by placing the point of view at the centre of the sphere, and taking for the picture a plane tangent Large globes are costly and inconvenient instruments; small ones do not exhibit sufficient details. It became necessary, therefore, to have recourse to pictures, which, on a plain surface, might give a representation to its surface. VOL. II. 50 |