WHY THIS TREATISE WAS WRITTEN. HAVING for many years openly defended the Philosophy of St. Thomas, even in what concerns the fundamental doctrines of organic and inorganic nature, we think it time to treat that subject, not merely touching on one or another point, but dealing with those doctrines philosophically. In Italy, where Masonic influence is now felt in every department of Government, nothing has been omitted by which the minds and hearts of our young men could be turned away, not only from the religious teaching of the Catholic Church, but also from all philosophical doctrines that are not against Religion. The teaching of Metaphysics was made over years ago to professors who only corrupted their pupils by the German transcendentalism of Kant, Hegel, Schelling and others but, inasmuch as that philosophy was abstruse, ill-suited to the wicked purpose intended and very apt to produce weariness, Metaphysics, properly so-called, were afterwards proscribed in the schools, to make way for Positivism and Materialism. If in our Catholic schools Physical Sciences were rightly and fully taught, the evil would be less. But what we call Government schools are, for the most part, obligatory; and, by reason of the method prescribed, even for private schools it is impossible to elucidate those doctrines without which the pupils are neither instructed sufficiently nor prepared for resisting the temptations of the Universities. By this treatise we cannot hope to be of use directly and immediately in the public schools of the Government: but we can hope to do something indirectly and mediately. In the second place, many who have a great reverence for the wisdom of the Angelic Doctor, and, in obedience to the Vicar of Jesus Christ, declare their adhesion to his doctrines, know too little of the fundamental questions that belong to Physics. Many have confused ideas about them, and therefore are liable to be taken in by the sophisms and the authority of men who pass as wise and learned in such things. Hence they either give in or vacillate, accepting as probable what is not only improbable, but also absurd and bad. These and other reasons have induced us to put before our readers, especially those who are given to the study of philosophy and natural sciences, that system which we call the Physical System, whose principles were certainly professed by the Angelic Doctor, St. Thomas. It is, or should be, unnecessary to say that we are not going to rake up exploded doctrines of the old physicists. The habit of confusing such opinions with the philosophical principles of rational Physics, ascribing to the latter what belongs to pure experiment, has led many to attack truth with the hatred due to error and to put the wisest in the category of quacks.