The progress of science during the past centuries has been in some measure energized by the development of new technologies. People are no more intelligent now than they were five centuries ago, or indeed five millenia ago. The differences are in the pool of past experience and the availability of means for manipulating the physical and mental environment. Until fairly recently, the development of new technologies in astronomy and geodesy has served primarily either to broaden the scope of phenomena that could be studied or to improve the precision with which one could examine already-studied phenomena. There seemed to be no likelihood that a situation could arise similar to that in particle physics, where the uncertainty principle indicates that the observation of the state of an object alters that state, affecting the observation. Indeed, we have not yet reached that point, but certain of the new techniques have introduced a degree of complication and inter dependence perhaps not previously encountered in the macro sciences. When observational capability is so fine that the data can be corrupted by the tidal motions of the instruments, for example, then there are a myriad of physical effects that must be considered in analyzing the data; the happy aspect of this is that the data can be used to study exactly these same effects. The complication does not, however, extend only to predictive computations against which the data are compared.

P.Brosche The development of the ideas and observational techniques related to the subject of our meeting "Tidal friction and the Earth's rotation," Bielefeld, September 1977 is one of the most fascinating books - not merely chapters - of the modern history of science. Its genealogical tree is as intricate as that of mankind itself: There are dead ends and superfluous re-discoveries. Due to these circumstances and to the pure extent of the topic, it is impossible to give more than a few highlights here. The first relevant observational fact was discovered by the famous English astronomer E. Halley in 1695 (Berry, 1961). He simply could not arrive at an agreement between ancient and recent eclipses using a constant mean angular motion of the Moon. Instead, he had to intro duce an empirical acceleration term in the mean motion. Known as the "secular acceleration," it has ever since been a most challenging sub ject of celestial mechanics and a main branch of the genealogical tree already mentioned. In 1754, completely independently and almost certainly in ignorance of those specialists' activities, the German philosopher Kant established the idea of tidal friction as a decelerating mechanism for the rotation of the Earth (Felber, 1974). Although he made some errors in his rough computations, the majority of the constitutive elements of his concept have survived to the present day (Brosche, 1977)."

The progress of science during the past centuries has been in some measure energized by the development of new technologies. People are no more intelligent now than they were five centuries ago, or indeed five millenia ago. The differences are in the pool of past experience and the availability of means for manipulating the physical and mental environment. Until fairly recently, the development of new technologies in astronomy and geodesy has served primarily either to broaden the scope of phenomena that could be studied or to improve the precision with which one could examine already-studied phenomena. There seemed to be no likelihood that a situation could arise similar to that in particle physics, where the uncertainty principle indicates that the observation of the state of an object alters that state, affecting the observation. Indeed, we have not yet reached that point, but certain of the new techniques have introduced a degree of complication and inter dependence perhaps not previously encountered in the macro sciences. When observational capability is so fine that the data can be corrupted by the tidal motions of the instruments, for example, then there are a myriad of physical effects that must be considered in analyzing the data; the happy aspect of this is that the data can be used to study exactly these same effects. The complication does not, however, extend only to predictive computations against which the data are compared."