It is extremely interesting to compare this old scholastic teaching with the modern ideas of the composition of matter and especially the notions which have come to us from researches in physical chemistry in recent years. Our scientists no longer believe that we have some eighty different elements, essentially different kinds of matter, that cannot by any chance or process be changed one {110} into another. We have seen one form of elementary matter changing into another, helium emanations becoming radium, have heard of Professor Ramsay's transmutation of various elements, and have about come to the conclusion that in the radio-active substances we have a wonderful transmuting power. A prominent American professor of chemistry declared not long since that he would like to treat a large quantity of lead ore in order to extract from it all the silver which so constantly occurs in connection with it in the natural state, and then having put the lead ore aside for a score of years, would like to examine it again, confident that he would find traces of silver in it once more, which had developed as a consequence of the radio-activity present in the substance and which is constantly changing lead into silver in small quantities. Newton's declaration, when he saw crystals of gold in connection with copper, that gold had been developed from the copper, seemed very foolish a century ago, but no one would consider it so at the present moment. We are prone to think that these old mediaeval philosophers accepting to some extent at least the philosopher's stone with its supposed capacity for changing baser metals into precious, and with their acceptance of the transmutation of substances, cannot have had any real scientific bent of mind. We are coming to the realization, however, that in many ways by pure reasoning, in {111} conjunction with such observation as they had at hand, they anticipated our most recent conclusions in very marvellous ways. We know now that radium, or at least radio-active substances, represent the philosopher's stone of the olden time. We are not surprised at the transmutation of metals and of substances, on the contrary, we are looking for it. I remember once stating the old theory of matter and form to a distinguished professor in chemistry in this country, and he was struck by the similarity of it to what are the present accepted ideas of the composition of matter. He asked why this teaching was not more generally known. I had to tell him that in every Catholic school of philosophy, it was taught as a basic doctrine, and that far from being concealed it was the very touchstone of Catholic philosophic teaching, and had often been the subject of deprecation and contemptuous remarks on the part of those who thought that it represented somewhat foolish old-fashioned teaching handed down to us from the backwardness and abysm of time.