De motu antiquiora ("The Older Writings on Motion"), or simply De Motu, is Galileo Galilei's early written work on motion (not to be confused with Newton's De motu corporum in gyrum, which shares the abbreviated name, De Motu). It was written largely between 1589 and 1592, but was not published in full until 1890. De Motu is known for expressing Galileo's ideas on motion during his Pisan period prior to transferring to Padua. Galileo left the manuscript unfinished and unpublished in his lifetime due to several uncertainties in his understanding and his mathematics. It is unclear whether this book was initially made out to be a book in the form of a dialogue or a more conventional way of writing. The reason for this is that Galileo worked on this book for many years, creating multiple copies of each section. In the last parts of his work, the writing style changes from an essay to a dialogue between two people who strongly uphold his views. Galileo would later incorporate select arguments and examples from his De Motu into his subsequent works Le Meccaniche (On Mechanics), Discorso intorno alle cose che stanno in su l'acqua (Discourse on Floating Bodies), and Discorsi e dimostrazioni matematiche intorno a due nuove scienze (Discourses and Mathematical Demonstrations Relating to Two New Sciences). Throughout De Motu, Galileo rejects Aristotle's views on the physics of motion, often with mocking tones, through various reductio ad absurdum arguments that demonstrate how Aristotle's assumptions on motion logically result in absurd conclusions that were contrary to observation or against his original assumptions, thus proving that the assumptions must be false. However, despite his frequent stinging criticism of Aristotle’s physics, Galileo’s De Motu still clung to the classical elements as a foundational cause for motion in which all matter moves toward its respective natural place in the universe. He further proposes an alternative theory to motion in which, instead of motion being propagated by the rushing of air (as was taught by the Peripatetics), it is believed that the true weight of a body can only be measured in a void, that the weight of the body in a medium is modified by its buoyancy in the medium (i.e., apparent weight), that the weight resulting from this buoyancy causes the body's natural motion, that projectile motion (distinct from natural motion) is believed to be the result of an impressed forced that modifies a weight of the projectile, and that the impressed force depletes over time much like how a hot object returns to its natural coldness. De Motu is notable for containing the earliest reference of Galileo’s interest in pendulums in which he observes that heavier objects would continue to oscillate for a greater amount of time than lighter objects. However, he misattributes this phenomenon as evidence that the impressed force in a moving body self-depletes faster in lighter bodies than in heavier bodies as opposed to air resistance having a greater effect on the lighter body. It’s questionable how much of Galileo’s ideas in De Motu were original. Some of the ideas of the De Motu are found in antiquity, others in the Middle Ages and among Galileo’s immediate predecessors in Italy. The subjects discussed in the essay are largely the subjects that had long been under discussion in academic circles, but while the solutions put forth by Galileo to individual problems are not, in general, original discoveries, the work as a whole gives a distinct impression of originality. This is due to the underlying unity of conception, the skillful linking of ideas, the constant recourse to mathematics, and the lucidity of the reasoning and the style. Source: Wikipedia (en)