It appears from the investigations of M. de Humboldt, that between the tropics the monocotyledonous plants, such as grasses and palms which have only one seedlobe, are to the dicotyledonous tribe, which have two seed-lobes like most of the European species, in the proportion of one to four; in the temperate zones they are as one to six; and in the Arctic regions, where mosses and lichens which form the lowest order of the vegetable creation abound, the proportion is as one to two. The annual monocotyledonous and dicotyledonous plants in the temperate zones amount to one-sixth of the whole, omitting the Cryptogamia (N. 214); in the torrid zone they scarcely form one-twentieth, and in Lapland one-thirtieth part. In approaching the equator, the ligneous exceed the number of herbaceous plants, in America there are a hundred and twenty different species of forest trees, whereas in the same latitudes in Europe only thirty-four are to be found.

Similar laws appear to regulate the distribution of marine plants. M. Lamouroux has discovered that the groups of algæ, or marine plants, affect particular temperatures or zones of latitude, though some few genera prevail throughout the ocean. The polar Atlantic basin, to the 40th degree of north latitude, presents a well-defined vegetation. The West Indian seas, including the Gulf of Mexico, the eastern coast of South America, the Indian Ocean and its gulfs, the shores of New Holland, and the neighboring islands, have each their distinct species. The Mediterranean possesses a vegetation peculiar to itself, extending to the Black Sea; and the species of marine plants on the coast of Syria and in the port of Alexandria differ almost entirely from those of Suez and the Red Sea, notwithstanding the proximity of their geographical situation. It is observed that shallow seas have a different set of plants from such as are deeper and colder; and, like terrestrial vegetation, the algae are most numerous toward the equator, where the quantity must be prodigious, if we may judge from the gulf-weed, which certainly has its origin in the tropical seas, and is drifted, though not by the gulfstream, to higher latitudes, where it accumulates in such quantities, that the early Portuguese navigators, Colum

bus and Lerius, compared the sea to extensively inundated meadows, in which it actually impeded their ships and alarmed their sailors. M. de Humboldt, in his Personal Narrative, mentions that the most extensive bank of sea-weed is in the northern Atlantic, a little west of the meridian of Fayal, one of the Azores, between the 25th and 36th degrees of latitude. Vessels returning to Europe from Monte Video, or from the Cape of Good Hope, cross this bank nearly at an equal distance from the Antilles and Canary Islands. The other bank occupies a smaller space, between the 22d and 26th degrees of north latitude, about eighty leagues west of the meridian of the Bahama Islands, and is generally traversed by vessels on their passage from the Caicos to the Bermuda Islands. These masses consist chiefly of one or two species of Sargassum, the most extensive genus of the order Fucoideæ.

Some of the sea-weeds grow to the enormous length of several hundred feet, and all are highly colored, though many of them must grow in the deep caverns of the ocean, in total or almost total darkness; light however may not be the only principle on which the color of vegetables depends, since M. de Humboldt met with green plants growing in complete darkness at the bottom of one of the mines at Freyberg.

It appears that in the dark and tranquil caves of the ocean, on the shores alternately covered and deserted by the restless waves, on the lofty mountain and extended plain, in the chilly regions of the north and in the genial warmth of the south, specific diversity is a general law of the vegetable kingdom, which cannot be accounted for by diversity of climate and yet the similarity, though not identity, of species is such, under the same isothermal lines, that if the number of species belonging to one of the great families of plants be known in any part of the globe, the whole number of the phanerogamous or more perfect plants, and also the number of species composing the other vegetable families, may be estimated with considerable accuracy.

Various opinions have been formed on the original or primitive distribution of plants over the surface of the globe; but since botanical geography became a regular

science, the phenomena observed have led to the conclusion that vegetable creation must have taken place in a number of distinctly different centers, each of which was the original seat of a certain number of peculiar species, which at first grew there and nowhere else. Heaths are exclusively confined to the Old World, and no indigenous rose-tree has ever been discovered in the New; the whole southern hemisphere being destitute of that beautiful and fragrant plant. But this is still more confirmed by multitudes of particular plants having an entirely local and insulated existence, growing spontaneously in some particular spot and in no other place; for example, the cedar of Lebanon, which grows indigenously on that mountain, and in no other part of the world. On the other hand, as there can be no doubt but that many races of plants have been extinguished, Sir John Herschel thinks it possible that these solitary instances may be the last surviving remnants of the same groups universally disseminated, but in course of extinction; or that perhaps two processes may be going on at the same time; "some groups may be spreading from their foci, others retreating to their last strongholds."

The same laws obtain in the distribution of the animal creation. The zoophyte (N. 215), occupying the lowest place in animated nature, is widely scattered through the seas of the torrid zone, each species being confined to the district best fitted to its existence. Shell-fish decrease in size and beauty with their distance from the equator; and as far as is known, each sea has its own kind, and every basin of the ocean is inhabited by its peculiar tribe of fish. Indeed MM. Peron and Le Sueur assert, that among the many thousands of marine animals which they had examined, there is not a single animal of the southern regions which is not distinguishable by essential characters from the analogous species in the northern seas. Reptiles are not exempt from the general law. The saurian (N. 216) tribes of the four quarters of the globe differ in species; and although warm countries abound in venomous snakes, they are specifically different, and decrease both in numbers and in the virulence of their poison with de

crease of temperature. The dispersion of insects necessarily follows that of the vegetables which supply them with food; and in general it is observed, that each kind of plant is peopled by its peculiar inhabitants. Each species of bird has its particular haunt, notwithstanding the locomotive powers of the winged tribes. The emu is confined to Australia, the condor never leaves the Andes, nor the great eagle the Alps; and although some birds are common to every country, they are few in number. Quadrupeds are distributed in the same manner wherever man has not interfered. Such as are indigenous in one continent are not the same with their congeners in another; and with the exception of some kinds of bats, no warm-blooded animal is indigenous in the Polynesian Archipelago, nor in any of the islands on the borders of the central part of the Pacific.

In reviewing the infinite variety of organized beings that people the surface of the globe, nothing is more remarkable than the distinctions which characterize the different tribes of mankind, from the ebony skin of the torrid zone to the fair and ruddy complexion of Scandinavia-a difference which existed in the earliest recorded times, since the African is represented in the Sacred Writings to have been as black as he is at the present day, and the most ancient Egyptian paintings confirm that truth; yet it appears from a comparison of the principal circumstances relating to the animal economy or physical character of the various tribes of mankind, that the different races are identical in species. Many attempts have been made to trace the various tribes back to a common origin, by collating the numerous languages which are or have been spoken. Some classes of these have few or no words in common, yet exhibit a remarkable analogy in the laws of their grammatical construction. The languages spoken by the native American nations afford examples of these; indeed the refinement in the grammatical construction of the tongues of the American savagés leads to the belief, that they must originally have been spoken by a much more civilized class of mankind. Some tongues have little or no resemblance in structure, though they correspond extensively in their vocabularies, as the Syrian

dialects. In all of these cases it may be inferred, that the nations speaking the languages in question are descended from the same stock; but the probability of a common origin is much greater in the Indo-European nations, whose languages, such as the Sanscrit, Greek, Latin, German, &c., have an affinity both in structure and correspondence of vocables. In many tongues not the smallest resemblance can be traced; length of time, however, may have obliterated original identity. The conclusion drawn from the whole investigation is, that although the distribution of organized beings does not follow the direction of the isothermal lines, temperature has a very great influence on their physical development. The heat of the air is so intimately connected with its electrical condition, that electricity must also affect the distribution of plants and animals over the face of the earth, the more so as it seems to have a great share in the functions of animal and vegetable life. It is the sole cause of many atmospheric and terrestrial phenomena, and performs an important part in the economy of nature.

SECTION XXVIII.

Of ordinary Electricity, generally called Electricity of Tension-Methods of exciting Bodies-Transference-Electrics and Non-Electrics-Law of its Intensity-Distribution-Tension-Electric Heat and Light-Atmospheric, Electricity-Its Cause-Electric Clouds-Back Stroke-Violent Effects of Lightning-Its Velocity-Phosphorescence-Phosphorescent Action of Solar Spectrum-Aurora.

ELECTRICITY is one of those imponderable agents pervading the earth and all substances, without affecting their volume or temperature, or even giving any visible sign of its existence when in a latent state; but when elicited developing forces capable of producing the most sudden, violent, and destructive effects in some cases, while in others their action, though less energetic, is of indefinite and uninterrupted continuance. These modifications of the electric force, incidentally depending upon the manner in which it is excited, present phenomena of great diversity, but yet so connected as to justify the conclusion that they originate in a common principle.