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Galileo and the Problem of Free Fall

Published online by Cambridge University Press:  05 January 2009

R. H. Naylor
R. H. Naylor
Affiliation:
Division of Philosophy, Thames Polytechnic, Wellington Street, London SE18 6PF.
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Extract

There can be little doubt that 1973 will remain notable as a year in which knowledge of Galileo's mechanics increased dramatically. Professor Stillman Drake's publication, in May, of some of Galileo's early work on the law of free fall was followed in the autumn by the publication of a number of important manuscripts clearly indicating Galileo's use of precise measurement. From a discussion of these manuscripts and Thomas Settle's performance of Galileo's inclined plane experiment, Drake implies that a clear view of Galileo's use of experiment is now emerging. Added emphasis was given to Drake's thesis that doubts concerning Galileo's use of experiment were largely unfounded, by James MacLachlan's realization of a Galilean experiment which was previously described as ‘imaginary’ by Koyré. The purpose of this paper is to suggest that, while it cannot be doubted that Galileo used experiment and precise measurement, his attitude to observation may well have been far more complex than Drake has supposed. My point of departure is James MacLachlan's remark that continuing disagreement over Galileo's use of experiment should lead to further examination of Galileo's experimental claims. I shall indicate that more than one view of Galileo's use of experiment may prove capable of explaining our present knowledge—a corollary of this being that alternative explanations may be proposed for the manuscripts recently published by Drake.

Type
Research Article
Information
The British Journal for the History of Science , Volume 7 , Issue 2 , July 1974 , pp. 105 - 134
Copyright
Copyright © British Society for the History of Science 1974

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References

The reconstruction of Galileo's inclined plane experiment was only made possible by the support and assistance received from my Faculty (Social Sciences and Humanities) and the Faculties of Science and Engineering at Thames Polytechnic. For this support, I am particularly grateful to Miss V. Pitt, Mr M. Yolles, Mr I. Bittle, and Dr R. A. M. Scott. The many discussions of this and other of Galileo's experiments with Dr Scott were of considerable help in the preparation of this paper.

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35 Galileo's units cannot be identified precisely. The braccio, translated variously as cubit or yard, ranged between 20 and 25 inches. Most Northern Italian cities appear to have had a standard braccio which seems to have been essentially a measure for cloth. In my view, Koyré was over-confident in stating that Galileo's braccio was ‘doubtless’ 20 inches (or 49 cms); it was probably not very different from this figure, though a value of around 22 inches seems most likely. The uncertainty on this issue is really of marginal significance, however. Mersenne had no doubts about Galileo's braccia; it was the measurement he suspected. Settle's comments on the doubts concerning the exact value of the units cannot explain Galileo's lack of knowledge of the rate of free fall. Settle believes that Galileo's braccia was close to 22 · 7 inches; see Settle, , op. cit. (3), p. 19Google Scholar. For Drake's views on Galileo's units, see Galileo, , Dialogue, op. cit. (8), p. 471Google Scholar. See also Skinner, F. G., Weights and measures (London, 1967).Google Scholar

36 Koyré, , op. cit. (5), p. 224.Google Scholar

37 Settle, , op. cit. (3), p. 20.Google Scholar

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39 Bernal, J. D., The extension of man. A history of physics before 1900 (London, 1972), p. 183Google Scholar. Bernal was unable to achieve success with the experiment, and he ascribed this to the fact that Galileo used better equipment. Bernal's interpretation of Galileo's description agrees well with mine; it seems clear that Bernal considered the parchment lining a refinement likely to lead to greater accuracy.

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