Book Reviews The Pulse of Time: Galileo Galilei, the Determination of Longitude, and the Pendulum Clock. BySilvio A.Bedini. Florence: Leo S.Olschki, 1991.Pp. xiv+ 132; illustrations, notes, appendixes, index. L 40,000.00 (paper). The opening of the world to oceanic navigation at the end of the 15th century was at once opportunity and challenge. From the start, it was apparent that access to distant lands was an avenue to wealth and power. Such access, however, called for important outlays of labor and capital and the development of new technologies. In particular, it was vital to learn how to locate oneself in the vastness of the empty sea without landmarks to guide. The problem was not in learning location north-south—that technique went back centuries. One simply read the altitude of the sun, took account of declination, and read off the latitude from tables. Half thejob done. Longitude (location east-west) was another matter. With the earth turning on its axis, celestial phenomena by themselves could not serve as a guide, for all points on a given parallel witnessed them in turn. The question was when: time was the key, for differences in time of perception could be converted into differences in distance (space). Given the importance of the longitude problem, it is not surprising that the rulers of that day wanted to promote inquiry. In fairy tales, they would have offered the hand of the princess in marriage; in real life, they offered prizes and honors important enough to draw to the task the best minds of the age. Yet I think the challenge alone would have been enough, for the longitude was a mystery of mythic proportions. Among those interested: Galileo Galilei. The Florentine scientist brought special credentials to the task. Aside from his extraordinary intelligence, he had been working in related areas of inquiry. For one instance, his experiments in telescopy suggested new possibilities of observable celestial events that could serve as temporal punctuation marks: the occultation, for example, of the now-visible moons ofJupiter. For another, his observation of the apparent isochronism of the circular pendulum opened the way to a new and better clock, one that might serve to establish the precise timing of celestial events or keep the time of a place of known longitude for comparison with time in situ. It is this story of Galileo’s venture into time and space that Silvio Bedini tells with the ease and erudition that comes from years of study and intimacy with the subject. It is a story that he tells matter-of-factly, Permission to reprint a review from this section may be obtained only from the reviewer. 670 TECHNOLOGY AND CULTURE Book Reviews 671 but one that reminds us again how much the world (and Italy in particular) lost by the Roman church’s suppression of free scientific inquiry. For Galileo came close to a solution, but his confinement under surveillance made it difficult for him to profit from the work of others and to pursue his speculations freely. Indeed, if there was any problem with his vision, it was an excessive optimism: the savant, especially in his later years, was ready to promise too much. “I have such a time-measurer,” he wrote the States General ofthe Netherlands in 1636, “that if four or six examples of this instrument were constructed and allowed to operate at the same time . . . they would show differences of only one second, not only from hour to hour but from day to day and month to month” (p. 20). If they were constructed. Galileo never got around to building one of his pendulum clocks. He was aware of the fine points that made all the difference between accurate and accurate enough: of the desirability, for example, of a pendulum making equal arcs; of the special difficulty of measuring time on shipboard; of the need, for temporal comparison of time at a place of known longitude and time in situ, of accurate predictions of the movement and positions of celestial bodies. And he had designed a good, workable machine with a dead-beat, semidetached escape ment of his invention. That it would have worked even...