The book describes the major physical theories of comets in the past two millennia. It demonstrates the evolution of ideas about the nature, position, motion and physical constitution of comets from Aristotle to Whipple. Unlike the available works on the history of comets, which either illustrate relatively short periods in the history of physical cometology or portray a landscape view without adequate details, the present study focuses on details of each theory. It also investigates the interaction between observational and mathematical astronomy, and the physical sciences in defining the properties of comets.

Ideas about the astrological aspects of comets are not considered in this study. Also, topics concerning the motion of comets are explained to the extent that is helpful in illustrating their physical properties. Although the present study is mainly focused on the physical theories of comets, its results will be relevant to studies in the history of geology, planetary science, and astrology. On the other hand, those results may initiate new studies about educational practices for physics and astronomy in post-Newtonian Europe, the ways that different parts of Newton's physical, astronomical and cosmological ideas evolved after him. Also, the debates about the constitution and chemical properties of comets in the post-Laplacian era may trigger new researches about possible influence of cometary studies on the foundation of astrophysics.

Zusammenfassung
Although the development of ideas about the motion and trajectory of comets has been investigated piecemeal, we lack a comprehensive and detailed survey of ph- ical theories of comets. The available works either illustrate relatively short periods in the history of physical cometology or portray a landscape view without adequate details. The present study is an attempt to review with more details the major physical theories of comets in the past two millennia, from Aristotle to Whipple. My research, however, did not begin with antiquity. The basic question from which this project originated was a simple inquiry about the cosmic identity of comets at the dawn of the astronomical revolution: how did natural philosophers and astronomers define the nature and place of a new category of celestial objects comets after Brahe's estimation of cometary distances? It was from this turning point in the history of cometary theories that I expanded my studies in both the pre-modern and modern eras. A study starting merely from Brahe and ending with Newton, without covering classical and medieval thought about comets, would be incomplete and leave the fascinating achievements of post-Newtonian cometology unexplored.

Inhalt
Aristotle's Theory of Comets.- After Aristotle.- From Brahe to Newton.- Comets in Newtonian Physics.- After Newton.- Non-Newtonian Theories of Comets.- Comets in the Laplacian Cosmos.- Comets in the Post-Laplacian Era.