Costa ben Luca gives an amusing explanation of how these processes take place in the brain. The opening between the anterior and posterior ventricles of the brain is closed by a sort of valve which he describes as “a particle of the body of the brain similar to a worm.” When a man is in the act of recalling something to memory, this valve opens and the spiritus passes from the anterior to the posterior cavity. Moreover, the speed with which this valve works or responds differs in different brains, and this fact explains why some men are of slow memory and why others answer a question so much sooner. The habit of inclining the head when deep in cogitation is also to be explained as tending to open this valve. However, the relative subtlety of the spiritus is another important factor in intellectual ability.
Views of other medieval writers.
Other medieval writers differed somewhat from these views of Costa ben Luca as to the nature of spiritus and the cavities of the brain. For instance, Constantinus Africanus in his treatise On Melancholy states that the spiritus of the brain is called the rational soul, which is inconsistent with the distinction drawn between soul and spirit in the other treatise. In the eleventh century both Constantinus in his Pantegni and Anatomy or De humana natura,[2648] and Petrocellus the Salernitan in his Practica;[2649] in the twelfth century both Hildegard of Bingen[2650] and the Pseudo-Augustinian Liber de spiritu et anima;[2651] in the thirteenth century both Bartholomew of England, who seems to cite Johannitius (Hunain ibn Ishak) on this point,[2652] and Vincent of Beauvais agree that the brain has three main cavities. The first is phantastic, from which the senses are controlled, where the sensations are registered, and where the process of imagination goes on. The middle cell is logical or rational, and there the forms received from the senses and imagination are examined and judged. The third cell retains such forms as pass this examination and so is the seat of memory.[2653] The Pseudo-Augustine, however, represents it further as the source of motor activity. Constantinus and Vincent of Beauvais, who quotes him in the thirteenth century, further distinguish the phantastic cavity as hot and dry, the logical cell as cold and moist, and the seat of memory as cold and dry. Moreover, the phantastic cell which multiplies forms contains a great deal of spiritus and very little medulla, while the cell of memory which retains the smaller number of forms selected by reason contains much medulla and little spiritus. Thus the general point of view of these other authors resembles that of Costa ben Luca despite the divergence from him in details. They perhaps also owe something to Augustine, who in his genuine works speaks of the three cells of the brain but makes the hind-brain the center of motor activity, and the mid-brain the seat of memory.[2654]
Thebit ben Corat.
Thabit ibn Kurrah ibn Marwan ibn Karaya ibn Ibrahim ibn Marinos ibn Salamanos (Abu Al Hasan) Al Harrani or Thabit ben Corrah ben Zahrun el Harrani, or Tabit ibn Qorra ibn Merwan, Abu’l-Hasan, el-Harrani, or Thabit ben Qorrah or Thabit ibn Qurra, or Tabit ibn Korrah, or Thabit ben Korra, as he is variously designated by modern scholars;[2655] or Thebit ben Corat, or Thebith ben Corath, or Thebit filius Core, or Thebites filius Chori, also Tabith, Tebith, Thabit, Thebeth, Thebyth, and Benchorac, ben corach, etc., as we find it in the medieval Latin versions—Thebit ben Corat seems the prevalent medieval spelling and so will be adopted here—was born at Harran in Mesopotamia about 836, spent much of his life at Bagdad, and lived until about 901.[2656] He wrote in Arabic as well as Syriac, but was not a Mohammedan, and Roger Bacon alludes to him as “the supreme philosopher among all Christians, who has added in many respects, speculative as well as practical, to the work of Ptolemy.”[2657] As a matter of fact, he was a heathen or pagan, a member of the sect of Sabians, whose chief seat was at his birthplace, Harran.
The Sabians.
The Sabians appear to have continued the paganism and astrology of Babylonia, but also to have accepted the Agathodaemon and Hermes of Egypt,[2658] and to have had relations with Gnosticism and Neo-Platonism. They seem to have laid especial stress upon the spirits of the planets,[2659] to whom they made prayers, sacrifices, and suffumigations,[2660] while days on which the planets reached their culminating-points were celebrated as festivals.[2661] They observed the houses and stations of the planets, their risings and settings, conjunctions and oppositions, and rule over certain hours of the day and night.[2662] Some planets were masculine, others feminine; some lucky, others unlucky;[2663] they were related to different metals;[2664] the different members of the human body were placed under different signs of the zodiac;[2665] and in general each planet had its own appropriate figures and forms, and ruled over certain climates, regions, and things[2666] in nature. Most of this, however, is astrological commonplace whether of pagans, Mohammedans, or Christians. Nor were the Sabians peculiar in associating intellectual substances or spirits with the planets.[2667] It was only in worshiping these and denying the existence of one God and in their practice of sacrificial divination that they could be distinguished as heathen or pagan. However, they seem to have devoted a rather unusual amount of attention to astrology and other forms of magic such as oracular heads,[2668] magic knots and figures,[2669] and seal-rings carved with peculiar animal figures. These last they often buried with the dead for a time in order to increase their virtue.[2670]
Thebit’s relations to Sabianism.
Thebit, at any rate, seems to have prided himself upon being a descendant of pagan antiquity. In a passage praising his native town he said, “We are the heirs and posterity of heathenism,”[2671] and he described with veneration a ruined Greek temple at Antioch.[2672] He had, however, some religious disagreement with the Sabians of Harran and was finally forced to leave.[2673] He met a philosopher who took him to Bagdad where he became one of the Caliph’s astronomers[2674] and founded there a Sabian community to his own taste. His numerous religious writings show the value which he attached to various Sabian usages and rites: ceremonials at burials, hours of prayer, rules of purity and impurity and concerning the animals to be sacrificed, readings in honor of the different planets.[2675]
Thebit as encyclopedist, philosopher, astronomer.