Responsum: On the Astrolabe

This Hebrew responsum clarifies the nature of a certain “tube” (shefoferet) that the Talmud reports that R. Gamliel used to determine distances of two thousand cubits (b. Eruvin 43b). In its immediate context, the Talmud is concerned with this tube because according to rabbinic law, one who arrives in an unpopulated area on the Sabbath eve may not travel beyond two thousand cubits unless he faces severe danger. The Talmud reports that when arriving on a boat prior to the Sabbath, R. Gamliel would determine through his “tube” whether they were close enough to a city that he and his fellows could travel to it on the Sabbath. Hayya explains the “tube” as a sort of primitive astrolabe, which is a scientific instrument used for navigation and, primarily, astronomy—and it includes a tube that was used for sighting objects.