Though Jews were not involved in the construction of the new clocks, they quickly reacted when tower clocks started ringing out in their towns; the earliest Jewish acknowledgments appear around 1400 CE, within a generation of the first major proliferation. Jewish reactions to the new technology played out differently in Italy and Ashkenaz; there was also a weaker response in the Ottoman Empire beginning in the sixteenth century after the Ottomans had begun importing the devices.
In Italy, acknowledgment of the mechanical clock appears frequently in the colophons of manuscripts; copyists began to indicate not only the date at which they finished a book, but also the hour, and book owners recorded the hours at which birth, deaths, and miraculous events took place. These colophons universally employ the “Italian hours,” a convention for using mechanical clocks in which the clock runs for a single 24-hour cycle beginning at sunset (so, for example, “22 hours” means two hours before sunset). Usage of this convention is so consistent that, I suggest, it can be used to determine the provenance of the author. (Italian hours were standard in Poland, as well).
In Ashkenaz, by contrast, rabbis began contemplating whether the ringing of the mechanical clock should be afforded legal significance. It was in these deliberations that the concept of “seasonal hours” first begins to appear regularly in Jewish texts; the term was most likely popularized in Hebrew following the 1492 Naples printing of Judah al-Ḥarīzī’s translation of Maimonides’ commentary on the Mishnah. While it is not clear whether the mechanical clock led to any immediate practical changes in the law, it forced rabbis to clarify regulations—or the gap between regulations and communal practice—in ways that had not previously been necessary.
In the seventeenth century, clocks and watches took a few important leaps forward in accuracy; in the early eighteenth century, the minute hand became a standard feature of clocks. With these advances in accuracy, new legal debates began to emerge. The legally-significant definition of how long it takes to walk a mil, for example, had ranged between 18 minutes (technically, 1/3 hour + 1/30 hour) to half an hour, but in practice most people would not have been able to distinguish the two; now that they could, it suddenly became important to justify the positions and determine which was to be followed. At the same time, increasing Christian toleration of Jews led to a change in how Jews employed clocks in the public square: from the eighteenth century, Jews began incorporating clocks into their portraiture and synagogue exteriors, although still in a limited fashion.