Shifting Standards: Experiments in Particle Physics in the Twentieth Century

Chapter 2 “Do Falling Bodies Move South?”

• 17 Edwin Hall, well-known for the discovery of the effect that bears his name,1 devoted two papers to a discussion of the question of whether falling bodies move south. The first paper, entirely devoted to the history of the subject, began with an admission that it was not an important scientific question.2 Hall’s commentary, however, on previous experiments and his method of data analysis, is both quite interesting and illuminating. Hall remarked that the question whether a sphere falling from rest through a few hundred feet of still air swerves perceptibly toward the south, from the vertical path indicated by the plumb line, is not, perhaps, one of the largest or most urgent problems of physics; but it has the dignity of venerable age and the charm of mystery. It was familiar to Newton; it has been answered in the negative, on theoretical grounds, by Gauss and Laplace, and in the positive, on experimental grounds, by nearly every one of the investigators who have from time to time through more than two centuries made the actual trial. (Hall 1903a, 179) He further noted that, “if the well-nigh universal agreement of experimental evidence as to the reality of such an effect is the result of a long succession of accidental errors in one direction, we have a striking exception to the ordinary course of chance events” (179). Hall then presented a detailed history and critique of previous experiments .3 He began with the work of Robert Hooke in the seventeenth century . He noted that Isaac Newton had written to Hooke remarking that a falling body would move in a spiral and be deflected to the east. Hooke, in a response before the Royal Society, disagreed: “On December 11[, 1679,] Hooke read to the society his answer to Newton’s letter, maintaining that the course of a falling body ‘would not be a spiral line as Mr. Newton seemed to suppose,’ and ‘that the fall of the heavy body would not be directly east, as Newton supposed; but to the southeast, and more to the CHAPTER 2 “Do Falling Bodies Move South?” 18 • “Do Falling Bodies Move South?” south than the east’” (181). On January 6, 1680, Hooke informed Newton that he had made three trials of the experiment, “in every one of which the ball fell towards the southeast of the perpendicular, and that very considerably , the least being above a quarter of an inch” (181). Hooke later reported two further successful trials. Hall wondered why Hooke was not more conclusive and suggested that it might have been due to the paucity of observations and the large deviation observed with a relatively small distance of fall. He also questioned whether Hooke was predisposed to see a positive effect because of his theoretical calculation and commitment: “Moreover, Hooke, a brilliant genius but a somewhat uncertain character, had committed himself in the most open way to the opinion that experiment would reveal a southerly deviation. In a man of his reputation such a bias is not to be overlooked; and yet it is hard to believe that he deliberately lied to his associates in the Royal Society” (182). Despite the possible bias, Hall concluded that Hooke’s “evidence is not to be altogether ignored” (182). This question of possible experimenter bias will appear several times in this book, and it is still an important issue. The next experiment reported by Hall was performed more than a century later. As he remarked, “left in this dubious state by Hooke, our problem appears to have remained untouched for more than a century” (182). In 1791 Guglielmini reported an experiment in which the height of fall was greater than that of Hooke, 78 meters as compared to 8.2 meters, and he found an average easterly deviation of 1.9 centimeters and a southerly deviation of 1.2 centimeters. Benzenberg, writing twelve years later, raised doubts. He noted that Guglielmini had not measured his perpendicular line until six months after he had performed the measurements.4 In 1802 Benzenberg conducted his own experiments. Using the tower of Saint Michael’s Church in Hamburg, he dropped 32 balls and found an average easterly deviation of 0.90 centimeters and a southerly deflection of 0.34 centimeters. Olbers suggested that air currents might be responsible for the positive result. Hall, once again, raised the question of possible experimenter bias: “Was Benzenberg in undertaking this research prepossessed in favor of a southerly deviation? Possibly...