VIII. Some remarks upon the method of observing the differences of right ascension and declination by cross hairs in a telescope

Abstract Those that are curious in observing the Heavenly Motions, and particularly myself, whose Business it is, are greatly obliged to the late Signior Cassini, for his Thought of applying Threads at half Right Angles in the common Focus of a Telescope, to determine thereby the differences of Right Ascension and Declination of any two Stars, whose situation is such, that by their diurnal Motion they follow each other through the Aperture of the Telescope,