D O C . 5 0 6 A N N I V E R S A R Y O F N E W T O N ’ S D E AT H 5 0 1 the running of a clockwork. Moreover, since it was obvious that the sequence of conscious processes was inseparably linked to material processes inside brains, it was inevitable to interpret the thought and will of animals and humans as also sub- ject to that strict causal regime. Thus Newton’s achievement exerted the most pro- found and lasting influence on our view of the world. But gravity is not the only force of nature. It does not explain cohesion, electrical effects, or light. However, Newton’s theory of motion seemed to deliver a sufficient basis for understanding all physical processes if one assumed the existence of other kinds of forces acting between particles of matter apart from gravity. Newton himself had already begun to further develop his theory of motion, for instance, by applying it to the theory of light. Hence he at least created a general framework for all natural laws that, it was hoped, would be capable of encompassing the laws of all events, by reducing all events to motions of particles under the influence of in- teracting forces. This program lasted into the second half of the 18th century and proved to be eminently fruitful in all areas of physics. Let us now try to take a glimpse at Newton’s intellectual workshop. Galileo and Kepler had already prepared the field for our great systematizer. Galileo recognized that ெundisturbed motion” was motion in a straight line and in constant motion.[7] Undisturbed motion should be understood as the motion of a body not influenced by others. This is the law of inertia. One can also express it this way: The velocity and direction of motion of a body are preserved as long as no external causes, so-called forces, act on the body. Galileo also already recognized that at the Earth’s surface the velocity of a freely released body increases down- wards under the influence of gravity by equal amounts within equal periods of time. Newton asked himself the general question: How does the velocity of a freely moving body change if an arbitrary, given force is acting upon it? This is a much more general question than the one treated by Galileo for, the acting force can change arbitrarily in direction and quantity over time, so the answer applied gener- ally to arbitrary motions of bodies and therefore had to contain the general law of motion. This problem could be solved with the help of Galileo’s inertia problem but for that, a new mathematical tool was needed which Newton first had to create for that purpose, namely, infinitesimal calculus. Newton was like a poet whose poems were so subtle that they demanded a novel kind of language for their formu- lation, which the poet himself first had to create. What actually is the velocity of an arbitrarily moving body conceived to be pointlike? Imagine an arbitrary motion of the body in two moments in time, fol- lowing each other in brief succession with the time difference IJ, the body is located in space at two very closely neighboring points P and G. The distance P–G is then [p. 38]