The science of mechanics, my dear Hermodorus, has many important uses in practical life, and is held by philosophers to be worthy of the highest esteem, and is zealously studied by mathematicians, because it takes almost first place in dealing with the nature of the material elements of the universe. for it deals generally with the stability and movement of bodies about their centres of gravity, and their motions in space, inquiring not only into the causes of those that move in virtue of their nature, but forcibly transferring others from their own places in a motion contrary to their nature; and it contrives to do this by using theorems appropriate to the subject matter.