friends. It is only the new and casual white who speaks of the African as a "nigger," and condemns the climate of the tropics. The whites have created valuable interests in the land; they understand the dialects of their workmen; and they know that the black who distinguished himself in his village, by his selftaught art and industry, in fashioning his fetish god, his light canoe, his elegant assegai or sword, may be taught to turn a screw at the lathe, to rivet a boiler-plate, to mould bricks, to build a stone wall or a brick arch. No one now advocates, like Monteiro, the introduction of coolies, or Chinese or European "navvies," to show the native African how to work. There are 7200 native navvies on the Congo railway, and all the stone piers and long steel structures which bridge the ravines and rivers, and the gaps cleft in the rocky hills, have been made by them. Twenty-five years ago, the explorer might land on any part of east or west Equatorial Africa, unquestioned by any official as to whither he was bound and what baggage he possessed. To-day, at every port there are commodious customhouses, where he must declare the nature of his belongings, pay duties, and obtain permits for traveling. In 1872, the whole of Central Africa, from one ocean to the other, was a mere continental slavepark, where the Arab slave-raider and Portuguese half-caste roamed at will, and culled the choicest boys and girls, and youths of both sexes, to be driven in herds to the slave-marts of Angola and Zanzibar. To-day, the only Arabs in Africa, excepting some solitary traders who observed the approach of civilization in time, are convicts, sentenced to hard labor for their cruel devastations.

Twenty-five years ago it took me eight months to reach Ujiji from the coast, whereas now it takes a caravan only three months. Up to four years ago it required five months to reach Uganda from the coast, but to-day loaded porters do the journey in less than ninety

days, while bicyclists have performed it in twenty-one days. Fourteen years ago the voyage from Stanley Pool to Stanley Falls was made by me, in the first steamer that was floated in the Upper Congo, in 379 hours. Now steamers accomplish the distance in 120 hours. In 1882-83 I was forty-six days going from Europe to Stanley Pool. The ordinary passenger in these times requires but twenty-five days; and two years hence the trip will take only twenty days.

Throughout the region now known as the Congo State death raged in every form, twenty-five years ago. Once a month, on an average, every village, of the hundred thousand estimated to be in the state, witnessed a fearful tragedy of one kind or another. In each case of alleged witchcraft, upon the death of a chief, a sudden fatality, the outbreak of a pest, the evil effects of debauch or gluttony, the birth of twins, a lightning stroke, a bad dream, the acquisition of property, a drought or a flood, ill luck or any mischance, native superstition demanded its victims according to savage custom. The Mganda, or witch - doctor, had but to proclaim his belief that expiation was necessary, and the victims were soon haled to the place of death. I should not be far wrong if I placed these public murders at a million a year for the state, and two millions for the whole of Equatorial Africa. Added to these was the fearful waste of human life caused by intertribal wars, the wholesale exterminations under such sanguinary

chiefs as Mtesa, Kabba Rega, Mirambo, Nyungu, Msidi, the destructive raids of such famous slavers as Said bin Habib, Tagamoyo, Tippu-Tib, Abed bin Salim, Kilonga-Longa, and hundreds of others. In fact, every district was a battlefield, and every tribe was subject to decimation.

I do not say that the awful slaughters resulting from native lawlessness and superstition have ceased altogether, but the 540 missions, schools, and churches,

and as many little military forts that have been planted across the continent with the aid of the steam flotillas of the Congo and the swift cruisers which navigate the great lakes, have completely extirpated the native tyrants and the Arab freebooters; and wherever military power has established itself or religion has lent a saving hand, the murderous witchdoctor can no longer practice the cruel

rites of paganism. But although in parts of the far interior there yet remains many a habitation of cruelty awaiting the cleansing light of civilization, there is every reason for believing confidently that the time is not far distant when Africa, neglected for so long, shall as fully enjoy the blessings of freedom, peace, and prosperity as any of her sister continents.

Henry M. Stanley.

I.

THE origin of the heavenly bodies was one of the earliest philosophical subjects which engaged the attention of the Greeks. With their keen sense of the beautiful and the orderly, and their genuine admiration of surrounding nature and of all celestial phenomena, they were the first to realize that the processes of cosmical evolution, by which the existing order of things has come about, must ever be regarded as one of the ultimate problems of the inquiring mind. Whence and how came the beautiful cosmos? was the question of the Ionian naturephilosophers of the seventh century. Yet with even so keen an interest in natural phenomena, the undeveloped state of the physical sciences in the pre-Socratic age permitted the acute reasoning of Anaximander and Anaxagoras, and also of Democritus and Plato at a later date, to reach only the general conclusion that the earth and other heavenly bodies had gradually arisen from the falling together of diffused atoms. After the decline of the ancient civilization and the advent of the less philosophical races and ideas which continued dominant till modern times, further advances in a purely speculative, not practical or moral

question could hardly be expected; and we meet with no important cosmogonic inquiry till the publication of Kant's Natural History and Theory of the Heavens, in 1755. In this work we have a distinct advance, based upon the laws of mechanics and of gravitation discovered in the preceding age by Galileo, Huyghens, and Newton; and hence the work of Kant is to be regarded as the first speculation founded upon exact physical laws. But in that age the whole question of cosmogony was so completely unfathomed, and so little was known of the universe of fixed stars, that Kant not unnaturally limited his inquiries to the most simple phenomena, and gave little consideration to the manifold detail with which all nature abounds. His most important contribution to cosmogonic thought consisted in the assumption (at that time nearly incredible) that the universe had not been created in a day or a week, but was the outgrowth of indefinite ages, under the operation of natural mechanical laws. Important as was this conception, and suggestive as was his theory of the formation of the planets from an extensive nebula originally including the whole solar system, it could hardly be expected that such heterodox ideas would get much consideration

in the circles of court philosophy dominating the middle of the eighteenth century. Accordingly, they gained little or no authority, or even notice, for many

years.

In the meantime France had become the centre of the philosophic world, and the great geniuses who adorned the Academy of Sciences just before and after the French Revolution—that strong impetus to new ideas, even though some should not survive the turbulent times in which they arose were destined to arouse and to fix philosophic attention on the sublime question of the formation of the heavenly bodies. Five celebrated geometers Clairaut, Euler, d'Alembert, Lagrange, and Laplace in the course of fifty years had well-nigh perfected the mathematical theory of gravitation; and Laplace, who had solved the problems which all his illustrious predecessors and contemporaries had declared to be insoluble, became above all others the dominant power in the scientific world. He had explained all known anomalies in the motion of the planets and the moon by the simple law of gravitation, and now for the first time it was possible to assign the exact places of the heavenly bodies in the most remote ages, account being taken of their mutual gravitation according to the Newtonian law.

Lagrange and Laplace had proved, under certain conditions holding among the planets, that the solar system would never be destroyed by the mutual gravitation of its parts, and hence they found no difficulty in conceiving its existence during past millions of years. After his unrivaled career of discovery, Laplace formed the design of presenting in his Système du Monde (published in 1796) a concise and luminous popular account of the existing state of astronomy, which he had done so much to perfect; and as if to add one more laurel to his brow, he inserted at the end of this work a Seventh and Last Note. This was the cel

ebrated nebular hypothesis, which from its origin at once commanded the attention of the age. In a short note of eleven pages the author of the Mécanique Céleste has condensed his theory of the formation of the planets and satellites. He conceives that at some remote epoch in the past the matter now constituting our system was expanded into a vast rotating fiery nebula extending beyond the limits of the outermost planet, and that as the heat radiated into surrounding space the mass gradually contracted, and by the law of the conservation of areas began to rotate more rapidly. As the mass accelerated its rotation by its gravitational condensation, the whole assumed the form of an oblate spheroid, a disk, or a double convex lens ; finally, at the periphery of the disk the centrifugal force became equal to the force of gravity, and as the contraction continued a ring of particles was left behind, revolving freely around the central mass. The condensation of this ring of matter would form the first planet, and so on for the other planets nearer the sun, as the nebula condensed. The planetary masses condensing and rotating in like manner would give birth to their satellites. This simple mechanical conception would account for the motion of all the planets in the same direction around the sun and nearly in the plane of its equator, and also for the rotations of the planets and satellites in the same direction in which they revolve in their orbits. The rings of Saturn were cited as a case of an uncondensed satellite, a model which had been left undisturbed to show us just how the system had formed.

The nebular hypothesis as thus outlined by the profound dynamical judgment and imaginative genius of Laplace was supported by Sir William Herschel's contemporary and independent discovery of all classes of celestial objects between the finished star and the embryo nebula, and this testimony to the truth of the

nebular hypothesis was afterward confirmed by Sir John Herschel's more critical survey of the nebula of the whole face of the heavens. But while both the mechanical speculations and the obser vations of the younger Herschel tended to support Laplace's views, the huge reflector of Lord Rosse, erected about the middle of the century, began to turn the scale of evidence the other way. Under the power of Lord Rosse's six-foot speculum some of the so-called nebula of Herschel were resolved into clusters, and the conclusion seemed imminent that under sufficient power perhaps all nebulæ might be resolved into discrete stars. Fortunately, the invention of the spectroscope about 1860, and Huggins's application of it to the heavenly bodies, showed that of the nebulæ are masses of many glowing gas gradually condensing into stars, and so far as possible realized the postulates laid down by Laplace. The confirmation arising from the demonstrated existence of real nebulæ in the sky was supplemented by Helmholtz's proof that the heat of the sun is maintained by the contraction of its own mass, and that our central luminary is therefore the core of the nebula first conceived by Laplace in 1796. The theoretical possibility of Laplace's assumption was further established by Lane's investigation of the condensation of gaseous masses, wherein it was proved that a cold nebula or diffused body of gas condensing under its own gravitation would rise in temperature; also by Lord Kelvin's researches on the age of the sun and the duration of the sun's heat; and by various researches into the actual conditions of the planets of the solar system.

But while all sound speculations since Joule's discovery of the mechanical equivalent of heat have confirmed the essential parts of the nebular hypothesis, other recent investigations have introduced modifications of which Laplace took no account. It is particularly of

these later discoveries, which throw an entirely new light upon the general problems of cosmogony, that we shall treat in this paper.

II.

Prior to the year 1875 the labors of astronomers and mathematicians had been devoted to the questions raised by Laplace over three quarters of a century before, and very little, if any, advance had been attempted on new lines, though many new researches and observations had been accumulating which confirmed the sagacity of the bold conceptions embodied in the Seventh and Last Note to the Système du Monde. About this time, the young mathematician G. H. Darwin, son of the illustrious naturalist, became occupied with certain tide-reductions undertaken by Lord Kelvin for determining the rigidity of the earth, and in the course of this work was led to develop the mathematical theory of the bodily tides which would arise in the earth on the supposition that it is not highly rigid as at present, but fluid, as, according to Laplace, it must have been at some past age. These researches were presented to the Royal Society between 1878 and 1882, and led to the conclusion that bodily tidal friction, as it is called, had played a prominent part in the cosmogonic history of the earth and the moon.

By tidal friction is meant the gravitational reaction arising from change of form due to tidal distortion of figure, with the resulting effects on the motions of bodies revolving around the tidally distorted mass; for the attraction of a heavenly body depends upon its form as well as upon its mass and distance. Now, when the moon raises tides in the earth, the form of the latter (in case it were fluid throughout) would not be spheroidal, but ellipsoidal or egg-shaped, with one end of the ellipsoid pointed somewhere in advance of the moon in its orbit. This tidal apex in the earth exercises a disturbing force on the moon's

motion, and in fact tends to accelerate the velocity in the orbit, which results in an increase in the moon's distance, and at the same time renders her orbit more eccentric, so that the earth is relatively nearer one end of her orbit the next time the moon goes round. This action is very minute, and, like the mills of God, grinds slowly, but in the course of immense ages, millions of years, the effects become very conspicuous and the whole character of the orbit is changed.

In this way, by a most profound analysis, Darwin showed that the moon was formerly much nearer the earth, and indeed a part of our globe, the whole probably rotating in about two hours and forty-one minutes; that the moon, after parting from Mother Earth, had been gradually driven away to its present distance by the tidal action of the fluid globe working over a great space of time. He was enabled to explain all the essential features of the system of the earth and moon, and, encouraged by this novel and unexpected result, wherein tidal friction had modified the course of evolution as predicted by Laplace, he tried to extend his new theory to other parts of the solar system. But while he found that tidal friction had played some part in the other planets of our system and in the system as a whole, the effects in general were much less considerable than in the case of the earth and moon, where the satellite is relatively quite large, amounting to one eightieth of the planet's mass; elsewhere the satellites are very small compared to the planet, and all the planets are very small compared to the sun. Where the attendant bodies are so small compared to the central body, the effects of tidal friction are greatly diminished; for, among other things, the effects depend on the mass and rotational velocity of the body in which the tides are raised. The mathematical methods which Darwin employed in his researches are extremely elegant, and in their line as appropriate as the proofs devised by his

father in the Origin of Species, but it would be vain to attempt any popular account of them. It must suffice to say that we can trace our moon through the most remote ages by a simple process of computation.

After Darwin had developed the theory of bodily tides and applied it to the planets and satellites, he gave his attention to other researches on the figures of equilibrium of rotating masses of fluid, with a view to finding out exactly what process is involved in the birth of a satellite from a planet. Just prior to the publication of his paper a similar investigation was made in France by Poincaré. Both geometers had essentially the same object in view, namely, the testing of Laplace's nebular hypothesis, and their results were identical in proving that a rotating mass (like the fluid earth when the moon was formed) would not break up into two extremely unequal parts, but that the two bodies would be fairly equal, or at least comparable, in size. Nor would the separation necessarily lead to the formation of a ring; the detached satellite might, and probably would, take instead the form of a lump or globular mass without the intervention of the annular form assumed by Laplace and previous investigators.

Comparing these results with the facts of the solar system, neither Darwin nor Poincaré could see that his profound researches had thrown much light upon the theories of cosmogony; for the satellites are quite small compared to their planets, and the planets are insignificant compared to the sun. I may remark

here that the sun has a mass 1047 times larger than that of Jupiter, the largest planet, and 746 times the mass of all the planets combined. In the formation of our system, therefore, substantially all the matter has gone into the sun. Here the case rested in the year 1888, with no indication of further advance along either old or new lines. Indeed, such advance might be considered the more