reached its maximum about the year 1855; and that this is near the maximum epoch of the secular period of the sun's spots. In Europe the tendency of the same general cause is to make the secular rate the least at the same epoch. In this way, probably, it has happened that the increasing secular rate of the easterly movement there has become nearly constant.'

Observation has furnished the means of testing the explana. tion we have given of the progressive change of declination. Dr. Loyd, in his discussion of the Dublin Observations (between 1840 and 1843), has established that the needle at Dublin has, from the vernal equinox until after the summer solstice, a motion in a direction opposite to the annual progression, and a motion in the other direction from the autumnal to the vernal equinox. The discussions of the observations at Philadelphia, and Toronto, have revealed a similar law at those stations, though the direction of the annual progression is reversed. Now, at Dublin the new currents developed at all seasons tend to give

From our present stand point we may obtain a distinct view of the origin of the diverse luininous phenomena of the Aurora Borealis, as well as of the attendant magnetic phenomena. We may perceive that the Aurora is a combined magnetoelectric and electro-magnetic phenomenon :-that the auroral light results from electric discharges along the lines of magnetic polarization that traverse the masses of solar matter, while passing over from the preceding to the following side of the earth's photosphere: that the discharges are in a great degree due to the demagnetizing action of the electric currents developed by the solar matter impinging upon the preceding side of the photosphere; but in part also to a direct disturbance of the electric equilibrium, along the lines of polarization, by these currents, or by the free electricity in the photosphere. We here allude, especially, to the more conspicuous auroras. It is conceivable that should there be an intermission in the reception of auroral matter from the sun, or the supply feeble, the currents continually excited in the earth's crust by the ether of space, may by augmenting the intensity of the earth's magnetism, originate currents in the photosphere, directed upward instead of downward. Such effects should be especially observable in the regions of greatest directive force. It is to be observed that the tendency of the demagnetizing action accompanying the more conspicuous auroras, with the attendant electric currents, is to disperse the auroral matter, and in this way to occasion its expulsion to an indefinite distance, under the operation of the repulsive force of the earth exerted upon single molecules, or minutely divided masses (see this Journal, vol. xxxviii, p. 70. The decrease of the earth's magnetizing action cooperates in this. There are several important probable inferences that may be drawn from the preceding discussion, which it may be advisable to state here, very briefly.

1. The sun must have become magnetized after the same manner as the earth, by reason of its rotation, and of its motion of rotation combined with its progressive motion through space. As in the case of the earth, there must be a continual development of new currents, tending to exalt its magnetic state. These new currents by this mode of action should condense the auroral matter of the photosphere, along the lines of polarization, and so develop both light and heat. The spots on the sun are probably due to an inverse effect (that is, demagnetizing and dispersing), produced by the electric currents directly developed in the photosphere, by the descent into it of cosmical matter, as the sun moves forward in space. According to this the faculæ and accompanying dark spots, have a similar origin to terrestrial auroras. Upon this theory the dark spots should be wanting at the magnetic equator, and at the poles. They should also be mostly confined to low latitudes (heliographical),

It is probable that a large fraction of the heat by which the temperature of the body of the sun is maintained is the result of the continual recurrence of the pro

the needle an easterly deflection; except near the autumnal equinox when their effect upon the declination will be slight. For the currents will run from S. of the magnetic E. to N. of the magnetic W., except at the autumnal equinox when they will be nearly perpendicular to the needle. In the annual inequality, therefore, the needle should be in its most easterly position at the vernal equinox, when the currents will be most oblique to the needle, and at its most westerly position toward the autumnal equinox. At Philadelphia and Toronto the secular change is due to the excess of the N. to S. currents, from the summer to the winter solstice, over the S. to N. currents from the winter to the summer solstice. Under the influence of these currents the needle should be in its most westerly position near the winter solstice, or near the close of the period during which the N. to S. currents are developed; and at its most easterly position near the summer solstice. The observations at these stations give results in entire accordance with these theoretical conclusions. But for the influence of the currents at other localities the amount of the inequality should be equal to the annual secular change. This was the case at Toronto (each 2', in the cess of magnetization by the impinging action of the ether of space (p. 66). The penetration of cosmical matter into the photosphere is another source of heat.

2. Similar inferences may be drawn with respect to the magnetic and thermal condition of the planets; and an approximate estimate may be made of the comparative condition of the different bodies of the solar system.

3. The continual development of heat in the entire mass of the earth, by the action of the ether, is probably the origin of those subterranean Titanic forces, which have so repeatedly, in past geological ages, fractured and upheaved certain portions of the earth's crust; and whose effects are now observable in earthquakes and volcanic eruptions. Upon this idea there should probably be certain lines of upheaval corresponding to the magnetic currents, in some of their shifting and comparatively stationary positions.

4. The rotating and revolving nucleus of a comet should become magnetized and heated in the same manner as the earth, and the sun, both in its mass and photosphere. In this fact we have the apparent origin of the formation and detachment of successive nebulous envelops, and of the emission of luminous jets from the nucleus;-the process of detachment and indefinite expulsion being the same as already alluded to, as in operation in the photosphere of the earth (p. 76). The same process attends the formation of the solar spots, and originates streams of nebulous matter, seen in the zodiacal light. The residual cometary phenomena, which remain unaccounted for by Olbers and Bessel's theory, as applied and amplified by the author (see this Journal, vols. xxvii, xxix, and xxxii, [2]) may be understood, in their minute details, in the light of the present conception.

5. It may be added, in confirmation of the theory of the continual descent of auroral matter, derived from the sun, into the earth's photosphere, that the diurnal variations of the electric tension near the earth's surface, are in accordance with the idea that free atmospheric electricity, for which no adequate terrestrial cause has yet been ascertained, is derived from the auroral matter thus received. Also, the diurnal variations of the barometer are other observed effects that should result, on mechanical principles, from the same general cause.

Again, the diminution in the hourly fall of the temperature, during the latter part of the night, for which no sufficient meteorological cause can be found, would seem to afford direct evidence of the heating effect that has been attributed to the resisting impulses received from the ether of space.

years from 1845 to 1851). At Philadelphia the annual progression, in 1843, was (4'4); more than double the annual inequality (2). This must be attributed to the preponderating action of the currents traversing those localities at which the needle was turning toward the west.

Unequal Magnetic Intensities of the two Hemispheres.-This has its origin in the unequal absolute velocities of the earth, near the equinoxes, resulting from the progressive motion of the solar system. A calculation from the most reliable data gives for the ratio of the maximum velocity (March 4,) to the minimum velocity (Sept. 6), 1.29. Now the ver. equi. currents determine the magnetic intensity of the southern hemisphere, in high latitudes, and the aut. equi. currents that of the northern hemisphere; and the ratio of intensities at the poles (dip 90°) should be nearly equal to that of the max. and min. velocities (129). According to Gauss's charts, its actual value is 1.32.*

[To be concluded.]

ART. XII.-The Distribution and Migrations of North American Birds; by SPENCER F. BAIRD, Asst. Sec. Smithsonian Institution. (Abstract of a memoir presented to the National Academy of Sciences, Jan., 1865.)

It is well known to all students of Natural History, that the zoology of America or the new world is very different from that of the old world, and that with these two grand divisions, there are in each various subdivisions of greater or less importance. To Dr. Sclater' is perhaps due the merit of having been the first clearly to define the "Regions" into which the animal life of the terrestial globe, the birds especially, may be divided, and to point out approximately their relative magnitude and boundaries as well as their comparative richness in species of birds. Some of his details have been corrected and improved by Mr. Wallace,' but the conclusions of Dr. Sclater are in the main those which have received the support of most naturalists of the present day, and his details will ever mark an era in the science of zoological geography.

Dr. Sclater, in the article above alluded to, presents the follow

It should have been stated in the text (p. 67) that the rotation of the earth virtually shifts the point of normal impact of the ether to the east of the 6 a. M. meridian; and so delays the morning critical hours.

We propose to discuss, very briefly, in the next No. of this Journal the remaining topic of our memoir,-Chemical Action.

'Journal of proceedings of the Linnæan Society: Zoology, ii, 1858, 130. (Read June 16, 1857.) Ibis, 1859.

2

ing scheme of the arrangement of "regions" as best illustrating their relationship.

The boundaries of these regions, as defined by Dr. Sclater with Mr. Wallace's corrections embrace the following countries. I. Palearctic Region.-All Europe and Africa north of the Sahara, and all continental Asia north of about the parallel of 30° N. lat. including the whole mountainous country and plateaus of Central Asia, as well as Japan and the Kuriles. The Aleutians, assigned by Dr. Sclater to this region, appear to belong more to North America.

II. Ethiopian Region.-This embraces all of Africa south of the Sahara, and on the eastern side all south of about 30° N. lat., as well as most of Arabia, except the portion along the Indian ocean and the Persian gulf. It includes also Madagascar, and the adjacent islands as Mauritius, Bourbon, etc. The Sahara Mr. Wallace considers as belonging to neither the Palearctic nor the African region, but to occupy the position of a sea, and to be essentially destitute of land species.

III. The Indian Region. This includes the low lands of continental Asia, about south of 30° N. lat. and the portion of Arabia excluded from the Ethiopian region, as well as Ceylon, Sumatra, Java, Borneo, and the Philippines. It is the country washed by the Arabian Sea, the Persian Gulf and the China Seas, and its southeastern limit passes between the islands of Bali and Lombok, between Borneo and Celebes, and between the Philippines and the Moluccas.

IV. The Australian Region.-This includes Australia, New Guinea, Tasmania, New Zealand and Polynesia, also Lombok, Celebes, the Moluccas, and the Sandwich Islands. Mr. Wallace calls attention to the fact of the very great dissimilarity between the fauna of Bali and Lombok, and of Borneo and Celebes, although geographically very near each other, while islands of the Indian region, as well as of the Australian, are respectively very closely allied, although much more remote from each other than those just contrasted. The explanation of this difference he finds in the comparatively slight depth of

water between islands of the same region, while the channel separating those of the different regions is almost unfathomable. By an elevation of 50 fathoms, all these islands of one region would almost become joined to the main land of their respective regions, while the channel separating the latter would still constitute a physical barrier. Hence he infers that subsequent to the original peopling of the Indian and Australian regions, a subsidence into the sea and the consequent production of islands, while it ultimately modified the minor characters of the faunæ, left the broad outlines unchanged.

V. North American Region.-Dr. Sclater divides this from the South American somewhere in Mexico, the line reaching farther north on the coast, and more to the south in the central mountainous portion. Wallace draws the line about the parallel of 220, or near the Tropic of Cancer. To the north it includes Greenland.

VI. South American Region.-This embraces, according to Sclater and Wallace, the rest of continental America, the West Indies, the Galapagos, the Falklands, etc., while Wallace even includes (very erroneously, however,) the Sandwich Islands.

Of the regions thus sketched out, I propose to confine myself to the two last mentioned, or those of the new world, and more especially the portion included in the United States and north of it, and to point out the minor subdivisions and peculiarities of the ornithological fauna of the same. Before proceeding however to this subject, I may premise that I cannot quite agree with Dr. Sclater in referring the West Indies to the South American Region, but prefer to consider it as having independent rank as:

VII. West Indian Region.-In winter a large proportion of the inhabitants of the islands are visitors from North America, but the summer fauna is very distinct. The islands nearest to North and South America have of course an impress of the characteristics of these continental areas respectively, but as a general law it may be stated that of the species of land birds peculiar to the West Indies, exclusive of the diurnal Raptores and Columbida, a large proportion belong to genera found equally in North and South America, as Vireo, Turdus, Mimus, Polioptila, Dendroica, Tyrannus, Myiarchus, Contopus, Myiadestes, Progne, Petrochelidon, Icterus, Sturnella, Colaptes, etc.: an almost equal proportion belong to genera peculiar to the West Indies, and characterizing several islands, as Gymnoglaux, Mimocichla, Spindalis, Phonipara, Tachornis, Loxigilla, Saurothera, Blacicus, Todus, etc. or else more or less peculiar to one island respectively as Teretristis, Melopyrrha, etc., to Cuba, Siphonorhis, Polytmus, Glossiptila, Hyetornis, Laletes, etc., to Jamaica, Dulus, etc., to

3

Todus Mexicanus of Lesson is a Porto-Rican species.