3. Kindi’s actual philosophy, like that of his contemporaries, consists, first and especially, of Mathematics and Natural Philosophy, in which Neo-Platonism and Neo-Pythagoreanism merge into one another. According to him no one can be a philosopher without studying Mathematics. Fanciful play upon letters and numbers is frequently met with in his writings. Mathematics he also applied to Medicine in his theory of the compound remedies. In fact he based the efficacy of these remedies, like the effect of music, upon geometrical proportion. It is here a matter of the proportionality of the sensible qualities, warm, cold, dry and moist. If a remedy has to be warm in the first degree, it must possess double the warmth of the equable mixture,—in the second degree, four times as much, and so on. Kindi seems to have entrusted the decision of this point to Sense, particularly to the sense of Taste, so that in him we might have a hint of the proportional relation existing between stimulus and sensation. Yet that view, though quite original, was with him a mere piece of mathematical play. However, Cardan, a philosopher of the Renaissance, on the ground of this doctrine, reckoned him among the twelve most subtle-minded thinkers. 4. In Kindi’s opinion, as has already been said, the world is a work of God, but His influence in its descent is transmitted through many intermediate agencies. All higher existence affects the lower, but that which is caused has no influence upon its cause, standing as this does above it in the scale of Being. In all the events of the world there is a pervading causality, which makes it possible for us, from our knowledge of the cause, to foretell the future,—for example, of the positions of the heavenly bodies. Farther, in any single existing thing, if it is thoroughly known, we possess a mirror, in which we may behold the entire scheme of things.