On Motive Forces

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Inasmuch as the compositions and effects produced by all sorts of machines are caused by the means of the four elements The "four elements"—fire, air, earth, and water—were the standard basis for physical science in the 17th century, derived from ancient Greek philosophy., which give body and movement to them, it seemed good to me to show the definition of each one in particular, and also some of their effects. As for their positions, the common and most widely accepted opinion of the Philosophers who have discussed their order has imagined fire above the air, and air above the earth and water; the first two being light and always seeking to rise upward, and the last two being heavy and always seeking to descend downward.

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FIRST DEFINITION

+ nourishment, it is subject to perish

There are two species of fire: one is elementary, which is not subject to corruption, and which I believe to be the heat of the Sun; for all other fire or heat requires nourishment, and that which requires nourishment is subject to perish. Therefore, the heat proceeding from the body of the Sun is the only elementary fire. The second species of fire is material fire, so called because it is nourished and maintained by physical matter; when this matter happens to fail, the heat also fails. As for why it is called luminous, this is because of the Sun, which is the true natural light, and likewise artificial light proceeds from material fire. Dryness is also present in it, which is seen in that it is the direct enemy of moisture, and even seeks to destroy it. Even those things we consider dry are further dried out by fire; for example, it is not common to believe there is any moisture in lead, yet experience shows us that lead sheets used to cover houses and churches dry out so much over time from the heat of the Sun that the metal shrivels and contracts original: "se cosine & retire." De Caus is describing the thermal expansion and contraction of lead roofing, which he interprets as a loss of internal moisture.. If the said sheets are tightly fastened against the wood so that they cannot contract, the sheets will crack in several places. Fire is also said to be very light for several reasons: first, because of its position, being above the other elements; and also because we see material fire rise upward with great lightness, appearing (as some Philosophers have said) as if it wishes to return to its place of origin. As for the force of fire, the greatest comes from material fire; everyone knows the damage it causes wherever it takes hold, whether by accident or deliberate undertaking. In Sicily, fire has taken hold within the hollow of Mount Gibella, otherwise called Etna original: "mont Gibella, autrement dit Ætna." "Gibella" comes from the Arabic word "Jebel," meaning mountain., which has been burning for a very long time; however, it is likely that this fire will end when all the sulfurous matter that maintains it is exhausted. The force of several inventions of war machines is also admirable, which are made with gunpowder original: "poudre à canon."; thus material fire serves us as well for doing harm as for doing good. As for elementary fire, there are several machines in this book which are moved by means of it, such as the raising of stagnant water and other following machines not demonstrated heretofore.