Page 350 - 89 history of astronomy_opt

orientation of his instruments, to the gradu-
ation of the arcs by the then new method of
transversals, and to the aperture sight used
upon his pointer. There were no telescopes
in his day, and no pendulum clocks. He
recognised the fact that there must be in-
strumental errors. He made these as small
as was possible, measured their amount, and
corrected his observations. His table of re-
350