The Day the Universe Changed - James Burke [63]
Copernicus had satisfied everybody’s demand that the hypotheses be as simple as possible and that they should ‘save the appearances’, or account for what heavenly phenomena appear to be, as exactly as possible. A fictional orbiting earth would do so. The scheme was taken up without demur, and used to reform the calendar in 1582. Again, ironically, it was a Lutheran who helped. In 1551 Erasmus Rheingold, Professor of Astronomy at Wittenberg, drew up new, improved celestial tables based on the Copernican figures. Dedicated to the Duke of Prussia, they are known as the Prutenic Tables and they formed the basis for the calculation of the new calendar.
The Germans were particularly experienced in astronomy because for more than a century the great mining cities of Nuremberg, Augsburg, Ulm and Regensburg had been centres of instrument-making. It was here, too, that the new cannons were best made.
The latest scientific and technological marvels of the early seventeenth century, including the newly discovered Americas, distillation, and the cannon which was to stimulate so much scientific research.
A gunner fires his cannon according to the laws of Aristotelian physics: the ball can only move up and down in straight lines.
Gunpowder had been in general use for only a hundred years. It had proved an immensely popular discovery with the princes of Europe, who had merely to indicate that they were passing a rebel town with artillery for that town to surrender. In the middle of the sixteenth century a new method of boring cannons was developed. This coincided with a cheaper way of casting stronger guns from bronze, and the increased accuracy of the muzzle encouraged greater care in aiming and firing. All over Europe engineers and gunners began looking for ways to fire more accurately. It was at this point that one of Copernicus’ minor heresies—placing the earth among the planets and blurring the separation between celestial and terrestrial conditions - was to become a vital element of momentous change.
The problem involved in analysing the movement of a cannon-ball was that there were confused ideas about what happened to the ball in the air. Aristotelian laws said that the natural state of all earthly objects was to be at rest. Since all heavy bodies had a natural ‘desire’ to be close to the centre of the earth they tended to remain static at the lowest position they could find. Motion in any direction away from the centre of the earth was impossible without a ‘mover’. Things also fell increasingly faster because they were happily moving towards their natural, lowest position. Any object that was ‘moved’ in another direction would cease to move once the action of the mover stopped. At this point, the object would seek happiness by falling straight to earth. While the object was still being moved along, its speed would relate to the amount of resistance it met from the surrounding medium. It was for this reason that Aristotle had said there could be no vacuum. If a vacuum existed bodies would be able to move from one place to another without resistance, instantaneously. Since this was never observed the vacuum did not exist.
The flaws in this argument were obvious even to the would-be faithful. Projectiles did not fall straight to earth, but followed a curved path. Arrows, released from the bow and the ‘mover’, did not fall immediately to the ground. The gradually changing force which appeared to be involved had been described first in Paris by two French clerics, Jean Buridan and Nicole Oresme. They called the force ‘impetus’, and by the fifteenth century, more than two hundred years after they had published their theory, it was widely accepted.
The impetus concept suited the Aristotelian idea that all things had ‘qualities’ of their own. Impetus would be the ‘quality of providing movement’. It was conceived of as a property acting much like the heat in a poker, generated inside the body, but exhausted through time. Motion caused impetus to appear in the body. The faster it went the