The Arabian magic as understood in Spain during the thirteenth century is very fully expounded in a curious work called _Picatrix_.[262] This book explains that the fundamental idea of the art was reaction leading up to transformation or magical change, adding that this reaction may be seen in three different regions of being; first among the elemental spirits themselves, next between these and matter, and, last, the reaction of one kind of matter upon another, as in alchemy. The second of these kinds of reaction admits the influence of earthly things upon the heavenly spirits, and is the foundation of that kind of magic which the _Picatrix_ proceeds to expound, in details which are often much more curious than edifying. This book has special value as showing the intimate relation between magic and the ordinary studies of those times. Aristotle is often quoted in it,[263] and the position of necromancy with regard to other branches of science is clearly defined. It is not hard to see that, when thus understood, this art must have allied itself closely with astronomy and astrology on the one hand, and with alchemy on the other. In the account given by Bacon of Avicenna’s philosophy, he says that the third great division of that author’s works, and one which had never appeared in Latin, was that devoted to the most hidden parts of natural philosophy.[264] The science of those days left an acknowledged place for the occult and the mysterious among its doctrines. This place was filled by magic, a study forbidden indeed by the Church, but generally recognised as occupying a real though secret department among the other sciences and arts. The tradition we so often meet with that masters of necromancy actually taught the art of magic in Toledo, Salamanca, and perhaps Padua, seems but a reflection in later times of what was then the genuine belief of European scholars. There is thus no reason why Michael Scot should not have devoted himself to what was the subject of actual and serious study during the times in which he lived, and especially so in the country where his chief literary labours were carried on. Were we to follow the mere likelihood of the case, his interest in astronomy and alchemy would lead us to think it very possible he might have studied an art that was so closely connected with these. But to change such a possibility into a certainty, or even a probability, something more convincing than any _a priori_ argument must be found. If no actual proof of Scot’s magical practice be forthcoming we must be content to leave the matter where we found it; in the realm of dim and unsubstantial tradition.[265]