Treatise on the Jewish Calendar

The three sections of this partially surviving Hebrew work, preserved in a single manuscript, address the seven days of creation, the rules of calendrical calculation, and cosmology and astronomy. In addition, when discussing how to set the calendar, Jacob reviews many practices associated with the Jewish year and invokes certain customs that are rooted in astrology. In this excerpt, he details the practice of northern European Jews to refrain from drinking water around the period of the seasonal equinox (known in Hebrew as the tekufah, here tequfah). Jacob staunchly defends this custom and relates each equinox to a momentous event in Jewish history. Others attacked the practice as superstitious or as based in an erroneous understanding of astrology.