The two works of Israeli which come in consideration for our purpose are those mentioned by Maimonides in his letter to Samuel Ibn Tibbon spoken of above, namely, the "Book of the Elements,"[30] and the "Book of Definitions."[31] Like all scientific and philosophic works by Jews between the ninth and thirteenth centuries with few exceptions, these were written in Arabic. Unfortunately, with the exception of a fragment recently discovered of the "Book of Definitions," the originals are lost, and we owe our knowledge of their contents to Hebrew and Latin translations, which are extant and have been published.[32] We see from these that Israeli was a compiler from various sources, and that he had a special predilection for Galen and Hippocrates, with whose writings he shows great familiarity. He makes use besides of Aristotelian notions, and is influenced by the Neo-Platonic treatise, known as the "Liber de Causis," and derived from a work of Proclus. It is for this reason difficult to characterize his standpoint, but we shall not go far wrong if we call him a Neo-Platonist, for reasons which will appear in the sequel. It would be useless for us here to reproduce the contents of Israeli's two treatises, which would be more appropriate for a history of mediæval science. A brief _résumé_ will show the correctness of this view. In his "Book of the Elements" Israeli is primarily concerned with a definite physical problem, the definition of an element, and the number and character of the elements out of which the sublunar world is made. He begins with an Aristotelian definition of element, analyzes it into its parts and comes to the conclusion that the elements are the four well-known ones, fire, air, water, earth. Incidentally he seizes opportunities now and then, sometimes by force, to discuss points in logic, physics, physiology and psychology. Thus the composition of the human body, the various modes in which a thing may come into being, that the yellow and black galls and the phlegm are resident in the blood, the purpose of phlebotomy, the substantial character of prime form, that the soul is not an accident, the two kinds of blood in the body, the various kinds of "accident," the nature of a "property" and the manner in which it is caused--all these topics are discussed in the course of proof that the four elements are fire, air, water, earth, and not seed or the qualities of heat, cold, dryness and moisture. He then quotes the definitions of Galen and Hippocrates and insists that though the wording is different the meaning is the same as that of Aristotle, and hence they all agree about the identity of the elements. Here again he takes occasion to combat the atomic theory of the _Muʿtazila_ and Democritus, and proves that a line is not composed of points. In the last part of the treatise he refutes contrary opinions concerning the number and identity of the elements, such as that there is only one element which