and sets over a certain other place, and he conceives that he has now obtained some definite information regarding the sun. His idea is, that the sun will go on always doing the same thing, and he therefore predicts to his fellows, who are less observant than himself, exactly where it will rise and where it will set. They join him in observing the luminary for a week or more, and the sagacity of our primeval astronomer is triumphantly vindicated: the sun is found doing as nearly as possible that which had been predicted of it.

63. These men have now got hold of the idea that the sun will always rise and set at the same places, that in fact his daily journey is always the same, and that he performs it in the same time. But in the course of six months they suspect they are mistaken Discredit is thrown upon the sagacity of our astronomer, and he broods over his disgrace for six months longer. At the end of this time, on turning his eyes towards the sun, what is his surprise and delight to find that luminary doing the very thing that he had all along predicted, returning once more to his old points of rising and setting,-places, we may presume, which could be easily remembered on account of some peculiarity of landscape. He is not yet prepared however for a higher generalisation, but again calls for his fellows, and while he suspects a certain amount of irregularity in the sun, yet succeeds in convincing them that his guess was after all not far from the truth. Once again he is reinstated in their good opinion.

64. However, six months after, precisely the same thing recurs once more; the rising and setting points

are now considerably different from those predicted. Our astronomer again loses credit, and regains it only partially six months afterwards, when the points are once more right. But he has now learned a lesson. He perceives a method in all this, and ultimately rises, by means of the difficulty, to a higher generalisation. He sees that the rising and setting points of the sun go through the complete series of their changes of position in about 365 days; and he has thus learned, in a rude way, that the sun has two motions, one of which he accomplishes in 24 hours, or one day, while the other has a period of 365 days, or one year.

65. While these things are in progress, a portentous and wholly unexpected event takes place: the sun for four minutes is totally extinguished. Our astronomer meditates much on this strange phenomenon, and is inclined to regard it as a triumph of the powers of Darkness, in personal conflict with those. of Light. Nevertheless he does not neglect to keep a record of the precise day on which it took place.

66. Years pass away, and our astronomer has passed away with them-he and all his generation; but a regular record is now kept of celestial occurrences, and especially of eclipses. At length it comes to be perceived that there is a periodicity even in such untoward phenomena, and an attempt is ultimately made, by means of this knowledge, to predict when the next eclipse will take place. It is perfectly successful, and the event loses from thenceforth much of its portentous significance.

67. Centuries roll on, and the apparent motions of the heavenly bodies have now been gradually reduced

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to system. The stars in particular are found to move, just as if they were attached to the roof of a great hollow vault which revolves round the earth once in twenty-four hours. But even amongst them there are five exceptions—namely, Mercury, Venus, Mars, Jupiter, and Saturn-which perform a sort of wandering or zigzag motion in the midst of their stationary brethren, and have in consequence received the name of planets. All, however, are supposed to move round the earth, which forms the centre of the universe.

68. In process of time, this superiority of the earth over the heavenly bodies comes to be questioned. There is a rising tendency to regard our earth as a somewhat insignificant member of a great system, rather than as something apart by itself. These tendencies are, however, strongly opposed by the authorities of a large section of the Christian Church, on the ground that the language employed in the Jewish Scriptures is against such a method of regarding the universe. Nevertheless the Copernican system ultimately prevails, and the planets and the earth are associated together as stars which travel round the sun; while the diurnal motion of the heavenly bodies is attributed to a motion of the earth round its axis. And we cannot help thinking that philosophers of the present day are too much disposed to undervalue the absolutely enormous stride that was made when the Copernican system was fully established.

69. But the planets are still supposed to move in perfect circles round the sun; for besides the fact that this hypothesis agrees very well with observation. there is a simplicity in the circle which leads philo.

sophers to believe that nature would adopt it in preference to any more complicated curve. Has it not been found that all apparent deviation from simplicity was in reality due to the fact that our point of view is a movable one, and does not this lead us to believe that the truth will be found in a circular orbit?

70. While such speculations are indulged in, Tycho Brahe is busy with his instruments. He is a thoroughly accurate man of science, and makes most excellent observations of the various planets. These are ultimately discussed by Kepler, who finds that the planets do not move round the sun in circles, but in ellipses, having the sun in one focus. He finds too that any one planet describes areas which are proportional to the times of description; while the squares of the periodic times of the various planets are proportional to the cubes of their mean distances from the sun. These are Kepler's laws; they are yet, however, only empirical. We know them to be true, but we cannot tell why they should be as they are and not otherwise.

71. It was reserved for the genius of Newton to show us why the planets should obey these laws, and to reduce the planetary system under the domain of ordinary mechanics. He succeeded in showing that every mass of matter attracts every other mass with a force which is directly proportional to the product of the masses, and inversely proportional to the square of the distance, and that this universal force accounts, not only for Kepler's laws of planetary motion but, for the orbit of the moon, as well as for that of a projectile discharged near the surface of the earth.

72. If we now pause for a moment, and review the progress of this investigation, we shall see that it began with a disposition to regard simplicity of motion as the test of truth, and when the Copernican system showed that our point of view is a movable one, it was at first thought that this would explain all departures from absolute simplicity. But Tycho Brahe and Kepler soon showed that the planets do not move in circles, and we now know that their motions, as well as that of the moon, can only be represented by curves of extreme complexity. Simplicity of motion has disappeared, but it has been replaced by simplicity of inter-relation between the various members of the system which are supposed to attract each other according to a simple and definite law. This law may be supposed to contain in itself implicitly all the various and complicated motions of the solar system. If applied to the past it will enable us to ascertain the exact date of the antient historical eclipses; if applied to the future it will enable us to foretell all but catastrophic astronomical occurrences.

73. Let us now turn to another branch of the same subject. When Galileo first applied his telescope to the sun, he discovered the existence of sun spots. Their solar origin was however for some time disputed, the schoolmen of that day, holding resolutely to the dicta of Aristotle, being indisposed to believe that there could possibly be any imperfection in the sun. The telescope alone was in fault. There was even a sermon preached on Galileo, the text of which was 'Viri Galilæi, quid statis in coelum spectantes?'

However, as time went on, observation showed