The library of the Vienna University Observatory houses an outstanding collection of historically significant scientific books on natural sciences from the 15th to the 19th century. Particularly in the German-speaking world, there are hardly any astronomical specialized libraries that possess a comparable historically developed collection. Completing the volume on works from the 15th to 17th centuries, this second volume presents the works of the 18th century. Each book available in the Vienna Observatory Library from the period between 1700 and 1799 is showcased with selected illustrations and bibliographic information. For a number of particularly noteworthy writings, such as those by Newton, Euler, Herschel, Maximilian Hell, and Johann Jakob von Marinoni, comments have been prepared that provide a cursory explanation of their content. The introductory, catalog, and commentary sections together illustrate how the spectrum of thematic focuses in astronomical research expanded throughout the 18th century, with the question of the nature and composition of celestial bodies coming to the forefront of interest.