Letters

Leonardo, Vol. 7, pp. 283-287. Pergamon Press 1974. Printed in Great Britain LETTERS Readers’ coninients are welcomed on texts published in Leonardo. The Editors reserve the right to shorten letters for reasons of space. Letters sliorrld be written in English or in French. ON ASTROLOGY AND MODERN SCIENCE (cont.) Bart J. Bok (Leonardo7,188 (1974))is, of course, correct in pointing out the error in Fig. 2 (Aries, the small constellation near Pisces, has been mislabeled as Leo) in my article (Leonardo 6, 121 (1973)). I regret the mistake and thank him for pointing it out. I applaud his reproaching fellow astronomers for not speaking out on the issue of astrology. However, I do find it somewhat incongruous that Bok faults the accuracy of Fig. 3, particularly since the thrust of my article was to attack the basic assumptions of astrology, rather than make statistical comparisons between prediction and observation. In fact, Fig. 3 was never meant to be accurate but was meant only to give a rough picture of the sky at sunrise from essentially anywhere on Earth, taking 6 a.m. as local time. One must remember that, in the 24 hours it takes the Earth to revolve, only the Moon will have moved as much as a third of a ‘house’, while the question of longitude merely shifts the horizon (ascendancy/descendancy line) in the hypothetical horoscope. I read with much interest the Note by Barth and Bennett in this issue (Leonardo 7, 235 (1974)), since they are examining the crucial point of basic assumptions . While it is quite true that the ultimate validity of a theory rests on its ability to make accuratepredictions, I do take issue with their and Friedman’s contention that assumptions are ‘irrelevant’ and need not be ‘realistic’. Perhaps in the field of economics unrealistic assumptions are in vogue but I can assure the readers of Leonardo that those working in the natural sciences make every attempt to be realistic in their choice of assumptions. What seems rarely to be recognized, however, is that these assumptions must take into account not only the phenomenon in question but also the means that are available for solving the problem once it has been conceptually modeled. Thus, many basic assumptions in physics, e.g. Einstein’s linear spring model for molecular forces in crystals, may appear unrealistic to the layman but one may be sure that the assumptions were the most realistic ones available, otherwise science would progress at a considerably slower pace. As for Barth and Bennett’s contention that ‘Kepler’s three Laws of Planetary Motion, however, were derived from assumptions about celestial harmony. ..’, I am forced to admonish them for their lax research and ambiguous referencing. Careful reading within the 97 pages they list in Koestler’s The SIeepwalkers reveals, on page 258, Kepler’s real assumptions concerning planetary motion: ‘Kepler’s answer was, that there must be a force emanating from the sun which drives the planets round their orbits. The outer planets move slower because this driving force diminishes in ratio to distance “as does the force of light” ’(italics, Koestler’s). Contrary to Koestler’s statement that Kepler’s ‘force’ has no relation to gravity, I would suggest that Kepler’s verbal description anticipates by 75 years Newton’s discovery of the l/d2law of gravitation (note: the intensity of a point source of light also diminishes with distance as 1/d2). Thus, it can be seen that Kepler’s assumptions concerning planetary motion are extremely ‘realistic’ indeed! With respect to the writings of Kepler, Galileo and other astronomers of the 16th and 17th centuries, the reader should be aware that they were writing with the practical concern of keeping their necks intact. It was distinctly dangerous to propose radical hypotheses concerning the cosmos and much of their work, including their letters, is couched in terms of prevailing opinions and language; hence, one of the tasks of a 16th century astronomer was to interpret the real meaning of texts by his colleagues. Later, Kepler’s fears were realized when his mother was accused of witchcraft on the basis of one of his books, Somnium, Sive Astronomia Limaris. She...