Rational mechanics soon became a vast and profound science. The true laws of the collision of bodies, respecting which Descartes was deceived, were at length known.
Huyghens discovered the laws of circular motions; and at the same time he gives a method of determining the radius of curvature for every point of a given curve. By uniting both theories, Newton invented the theory of curve-lined motions, and applied it to those laws according to which Kepler had discovered that the planets describe their elliptical orbits.
A planet, supposed to be projected into space at a given instant, with a given velocity and direction, will describe round the sun an ellipsis, by virtue of a force directed to that star, and proportional to the inverse ratio of the squares of the distances. The same force retains the satellites in their orbits round the primary planets: it pervades the whole system of heavenly bodies, and acts reciprocally between all their component parts.
The regularity of the planetary ellipses is disturbed, and the calculation precisely explains the very slightest degrees of these perturbations. It is equally applicable to the comets, and determines their orbits with such precision, as to foretel their return. The peculiar motion observed in the axes of rotation of the earth and the moon, affords additional proof of the existence of this universal force. Lastly, it is the cause of the weight of terrestrial bodies, in which effect it appears to be invariable, because we have no means of observing its action at distances from the centre, which are sufficiently remote from each other.
Thus we see man has at last become acquainted, for the first time, with one of the physical laws of the universe. Hitherto it stands unparalleled, as does the glory of him who discovered it.
We may distinguish the progress of each science as it is in itself, which has no other limit than the number of truths it includes within its sphere, and the progress of a nation in each science, a progress which is regulated first by the number of men who are acquainted with its leading and most important truths, and next by the number and nature of the truths so known.
In fine, we are now come to that point of civilization, at which the people derive a profit from intellectual knowledge, not only by the services it reaps from men uncommonly instructed, but by means of having made of intellectual knowledge a sort of patrimony, and employing it directly and in its proper form to resist error, to anticipate or supply their wants, to relieve themselves from the ills of life, or take off the poignancy of these ills by the intervention of additional pleasure.
The history of the persecutions to which the champions of liberty were exposed, during this epoch, ought not to be forgotten. These persecutions will be found to extend from the truths of philosophy and politics to those of medicine, natural history and astronomy. In the eighth century an ignorant pope had persecuted a deacon for contending that the earth was round, in opposition to the opinion of the rhetorical Saint Austin. In the seventeenth, the ignorance of another pope, much more inexcuseable, delivered Galileo into the hands of the inquisition, accused of having proved the diurnal and annual motion of the earth. The greatest genius that modern Italy has given to the sciences, overwhelmed with age and infirmities, was obliged to purchase his release from punishment and from prison, by asking pardon of God for having taught men better to understand his works, and to admire him in the simplicity of the eternal laws by which he governs the universe.
Meanwhile, so great was the absurdity of the theologians, that, in condescension to human understanding, they granted a permission to maintain the motion of the earth, at the same time that they insisted that it should be only in the way of an hypothesis, and that the faith should receive no injury. The astronomers, on the other hand, did the exact opposite of this; they treated the motion of the earth as a reality, and spoke of its immoveableness with a deference only hypothetical.
In the course of a redshift survey of galaxies brighter than R approximately equal to 16.3, 133 redshifts were measured in three fields, each separated by roughly 35 deg from the other two. If the galaxies in these fields were distributed uniformly, the combination of a galaxian luminosity function and the magnitude limits predicts that the distribution of redshifts should peak near 15,000 km/s. In fact, only one galaxy of the 133 was observed with a redshift in the 6000 km/s interval centered on 15,000 km/s. One plausible interpretation is that a large volume in this region of order 1,000,000 cu Mpc is nearly devoid of galaxies.
When the movement of the comets is considered and we reflect on the laws of gravity, it will be readily perceived that their approach to Earth might there cause the most woeful events, bring back the deluge, or make it perish in a deluge of fire, shatter it into small dust, or at least turn it from its orbit, drive away its Moon, or, still worse, the Earth itself outside the orbit of Saturn, and inflict upon us a winter several centuries long, which neither men nor animals would be able to bear. The tails even of comets would not be unimportant phenomena, if in taking their departure left them in whole or part in our atmosphere
When they [radio astronomers] grew weary at their electronic listening posts. When their eyes grew dim with looking at unrevealing dials and studying uneventful graphs, they could step outside their concrete cells and renew their dull spirits in communion with the giant mechanism they commanded, the silent, sensing instrument in which the smallest packets of energy, the smallest waves of matter, were detected in their headlong, eternal flight across the universe. It was the stethoscope with which they took the pulse of the all and noted the birth and death of stars, the probe which, here on an insignificant planet of an undistinguishable star on the edge of its galaxy, they explored the infinite.
Every 12 years Jupiter returns to the same position in the sky; every 370 days it disappears in the fire of the Sun in the evening to the west, 30 days later it reappears in the morning to the east...
The astronomer is, in some measure, independent of his fellow astronomer; he can wait in his observatory till the star he wishes to observe comes to his meridian; but the meteorologist has his observations bounded by a very limited horizon, and can do little without the aid of numerous observers furnishing him contemporaneous observations over a wide-extended area.
A star is drawing on some vast reservoir of energy by means unknown to us. This reservoir can scarcely be other than the subatomic energy which, it is known exists abundantly in all matter; we sometimes dream that man will one day learn how to release it and use it for his service. The store is well nigh inexhaustible, if only it could be tapped. There is sufficient in the Sun to maintain its output of heat for 15 billion years.
The zodiacal light is caused by sunlight reflecting from meteoric dust that orbits the sun in the plane of the solar system, remnants of the vast nebula of dust and gas out of which the solar system was born more than four billion years ago. Like the planets, this diffuse stream of particles reflects light, although faintly and rarely seen. Moonless nights of winter are the best time to see the zodiacal light. and nowhere better than here, on the Tropic of Cancer, where the plane of the solar system is tipped so as to pass directly through our zenith, lifting the band of faint light up and away from the horizon. And so we were treated to the spectacle of two intersecting rivers of lights, the light of two great whirling disks, the solar system and the galaxy. The solar system is tipped on its side within the greater disk of the galaxy, so the two rivers of light intersect more or less at right angles. The axis of the Earth is tipped within the solar system, and our bodies were tipped with respect to the axis of the Earth. We struggled to orient ourselves to these many cockeyed angles. In the twenty minutes we stood gaping at the light-streaked sky, our spinning planet carried us 350 miles to the east. The flight of the Earth around the sun whirled us 22,000 miles through the space of the solar system. The turning galaxy bore us 200,000 miles through the cosmic abyss. We felt like the prophet Ezekiel, who saw in the heavens intersecting wheels turning upon wheels, sparkling like chrysolite. It was enough to cause vertigo.
Almost 1000 years ago, Chinese astronomers observed a new star visible in the daytime sky, which they called a “guest star.” This supernova created what we now observe telescopically as the Crab Nebula. It is interesting that nowhere in Western Europe was this transient object recorded. Church dogma at the time declared the heavens to be eternal and unchanging, and it was much easier not to take notice than to be burned at the stake. Almost 500 years later, European astronomers had broken free enough of this dogma so that the Danish astronomer Tycho Brahe was able to record the next observable supernova in the galaxy.