are well known and constant visitors in the region of the Great Slave Lake. Several species of water birds that belong to the winter fauna of the Pacific coast resort to the Slave Lake region and north of it to breed, crossing the Rocky Mountains for the purpose. Among them may be mentioned Larus Californicus and brachyrhynchus, Colymbus Pacificus, Bernicla nigricans, Anser Rossii, etc. This, however, may be in consequence of their migrations being along a meridian line, or north and south; the meridian of the westernmost point of California and even of Vancouver's Island passing east of the mouth of the Mackenzie River. In any investigation into the reasons why the eastern province is of so much greater extent than the others, and exhibits such a trend westward in British America as to reach and even cross the Rocky Mountains, we will be greatly aided by the examination of Prof. Guyot's Wall Map of North America. On this map the country, not exceeding 800 feet in height, is colored green, and this portion is almost exactly coincident with the limits of the eastern province just defined reaching west of the Mississippi, almost to the edge of the fertile plains (the true zoological boundary), passing up the Mississippi via St. Paul to the Winnipeg valley, involving the whole shores of Hudson's Bay, thence in a northwesterly direction, a little south of Slave Lake to the foot of the Rocky Mountains, and north to the Arctic ocean on both sides of the Mackenzie. Within this vast country are "islands" of more elevated land; the whole Appalachian range, from New Brunswick to Central Georgia and Alabama; the height of land between Hudson's Bay and the St. Lawrence system of waters (nearly parallel with the latter), the plateau of Iowa and Northern Wisconsin, and that east of Slave Lake," etc, being more or less completely encircled by the lower level referred to. The highlands within this region have to a certain extent a peculiar fauna, characterized by the presence of such species to a considerable degree even in summer, as Junco hyemalis, Perisoreus Canadensis, Chrysomitris pinus, Curvirostra Americana (more rarely leucoptera), Pinicola Canadensis, etc., most of which are known to breed in the high mountain region of Georgia. These highlands do not, however, materially alter the summer distribution of our birds, especially in the interior, and there is no physical obstacle, not even that 10 This region, bounded west by Coppermine river, Slave, Athabasca, and Wollaston lakes, and south by Churchill river, is known as the Barren Grounds of Arctic America, and is a great granitic or azoic region, more or less barren of vege tation, destitute of large trees, and having few inhabitants. It is, however, the especial home of the Musk Ox, the Barren Ground or Small Reindeer, the Barren Ground Bear, the Polar Hare, and other species. of temperature, to interrupt or affect their passage by way of Rupert's land to the shores of the Arctic ocean." The southern division of the eastern province is also quite well outlined by Prof. Guyot's limits of the cotton-producing region, although running much farther to the northwest in Arkansas and the Indian Territory than there indicated. The much greater tendency of the southern birds, or those belonging to the cotton region, to go northward in the Mississippi valley than along the Atlantic slope is explained not only by the ascent there of the isothermal lines, but by the absence of any such obstacle to their journey as is furnished by the Appalachian range. The great central plateau region of Prof. Guyot's map corresponds quite closely with the middle ornithological province, reaching north to the Saskatchewan and west to the Pacific slope. The close relationship of the western province to the middle is illustrated by the fact that the region of country exceeding 800 feet in height, extends quite to the Pacific in most places, leaving only a few narrow borders and perhaps the valley of the San Joaquin and the Tulare lakes below that level. It is a fact not without its significance that the depressed lowland area of eastern America is characterized by the existence of certain genera of fishes and reptiles not found in its Appalachian "island." Thus we have Amia, Lepidosteus, Micropterus (Grystes), and various other forms of fishes throughout the Mississippi valley as far north as the Great Lakes, while in the Atlantic slope they do not pass the James or Lower Potomac except as stragglers. The soft shelled turtles, and the great mass of the "The Appalachian Region towards the north and northeast passes into a well marked subdivision, called by Prof. Verrill in his paper on the birds of Norway, Maine, the "Canadian." This he correctly characterizes by the presence of certain species during the breeding season, replacing certain near allies, in what, with Prof. Agassiz, we may term the Alleghanian subdivision. Some of the characteristic and more or less parallel species of birds in these two subdivisions he considers to be the following: Alleghanian. Dendroica discolor, Canadian. Perisoreus Canadensis, The Canadian sub-province includes especially the highlands between Hudson Bay and the St. Lawrence waters and across them into Northern Wisconsin, the higher portion of the Adirondack, Green, and White Mountains, Northern Maine, and, according to Prof. Verrill, the coast region from Mt. Desert to the southeastern part of New Brunswick, including the islands in the Bay of Fundy. Even far to the south, the high mountain regions of the Alleghanies to Georgia have the same fauna, their most characteristic species of bird being the common blue snowbird, Junco hyemalis. Emydida belong to the same low region also, as well as most of the American Perennibranchiate Amphibia, Menopoma (more rarely Menobranchus) alone penetrating into the Appalachian region, while Siredon belongs exclusively to the high central plateau, being found from the Missouri plains to the Cascade mountains of Oregon and south to the city of Mexico. The Unionidae and Melaniadae seem likewise to belong more especially to the depressed portion of eastern North America. I may also mention in this same connection that as might be expected, the entire eastern province is characterized by its abundance of Chelonians and Amphibians; the middle and western, by their Saurians. Among fishes the Etheostomoids, Esoces, Siluridae, the fresh-water Ganoids, (Amia, Lepidostei, etc.), the fresh-water Percoids, etc., are peculiar to the eastern province, while the great abundance of unusual forms of the Cyprinida is equally distinctive of the middle and western. As regards the fishes, however, the boundaries of the provinces are considerably changed, the eastern including all the waters emptying into the Missouri river and Gulf of Mexico, the middle embracing the region of the Great Basin and the drainage of the Colorado river, and the western, the waters discharging into the Pacific. The following tables present the species of birds most characteristic of each province-the selection having been mainly confined to what may be considered as representative species, or those which would formerly have been considered as identical. The isolated species of each province have not been included. To sum up in brief the conclusions reached in the preceding remarks, it may be stated that the ornithological provinces of North America consist of two great divisions of nearly equal size in the United States, meeting in the vicinity of the 100th meridian, the western half divisible again into two, more closely related to each other than to the eastern, though each has special characters. These three sections form three great provinces to be known as the western, middle, and eastern; or those of the Pacific slope; of the great basin, the Rocky mountains and the adjacent plains; and of the fertile plains and region generally, east of the Missouri. A northern or sub-arctic fauna mixes with and melts into the three, extending far to the south (even into Mexico) along the Rocky mountains. The middle and eastern provinces have each a southern subdivision, the one bordering on Mexico, the other on the Gulf and the Atlantic, and each of these also exhibits a differentiation, the former having a special "Found also in the middle province. "Extends also to the Rocky Mts. "Found all the way across to the Pacific. 15 Found also at Fort Tejon? AM. JOUR. SCI.-SECOND SERIES, VOL. XLI, No. 121.-JAN., 1866. subdivision again into Cape St. Lucas, and the latter into Florida. Northward the eastern province extends more and more westward reaching the Rocky mountains and even west ward of them towards the Yukon. The southern boundary of the middle province of North America may be arbitrarily established as a straight line, drawn from the mouth of the Rio Grande to that of the Yaqui near Guaymas on the Gulf of California, thus throwing into North America the whole of Florida and Lower California. [To be continued.] ART. XIII.-Experiments on Mechanical Polarity; by PLINY EARLE CHASE. M.A., S.P.A.S. [Continued from vol. xl, p. 316.] C. APPARATUS-POLARITY. FRICTION and the jarring of the apparatus, modified by the degree of velocity imparted to the ring, produce a polarity of their own which should be carefully estimated, and due allowance made for its influence in all delicate and doubtful experiments. In order to determine the directivity of the normal vibrations, independent of any mere current influence, the needle was shielded by a glass, as in the ordinary surveyor's or mariner's compass. 27. When the axis is in the meridian, the polarity appears to be meridional. 28. With the axis in the equator, the polarity is also meridional. 29. If the northern extremity of the axis is inclined to the west, the needle declines to the east. 30. Giving the axis an easterly inclination, the needle declines to the west. The declination is, therefore, from the axis in all cases, and we may infer that the earth's rotation exerts a constant tendency to increase the normal declination of the needle. 31. In all positions of the axis there appears to be a slight disposition in the needle to decline to the east, independent of the motion produced by the mere vibration of the apparatus. If this disposition is owing to terrestial currents, it is probable that the declination would be westward in the southern hemisphere, in accordance with Ferrel's law, that, "in whatever direction a body moves on the surface of the earth, there is a force arising from the earth's rotation which deflects it to the right in the northern hemisphere, but to the left in the southern.” (Math. Monthly, i. 307.) 'From the Proceedings of the American Philosophical Society, vol. x, pp. 155–161. |