Muḥyi
MUḥYI ’LDīN ALMAGHRIBī (MUḥYI ’IMILLA WA ’LDīN YAḥYā IBN MUḥAMMAD IBN ABI ’ISHUKR ALMAGHRIBī’ ALANDALUSī)
(fl. Syria, and later Marāgha, ca. 1260–1265)
trigonometry, astronomy, astrology.
AlMaghribī was a HispanoMuslim mathematician and astronomer, whose time and place of birth and death cannot be determined. Little is known about his life except that he was born in the Islamic West and flourished for a time in Syria and later in Marāgha, where he joined the astronomers of the Marāgha directed by Nạṣir alDīn alṬūsī. He made observations in 1264–1265. It has been said that he was a guest of Hūlāgū Khān (īlkhān of Persia, 1256–1265) and met Abu ’1 Faraj (Bar Hebraeus, 1226–1286).
Suter and Brockelmann ascribe quite a long list of writings to alMaghribī.
Trigonometry
1. Kit̄b shakl alqạ̣̄’ (“Book on the Theorem of Menelaus”).
2.Ma yanfari’u ’an shakl alqạ̣̣̄ (“Consequences Deduced From shakl alqạ̣̄’”).
3.Ris̄la f̄ kayfiyyat istikhr̄j aljuȳb alw̄qi’a fi͗ld̄’ira (“Treatise on the Calculation of Sines”). Astronomy
4. Khul̄ṣat alMajiṣṭ̄(“Essence of the Almagest”). It contains a new determination of the obliquity of the ecliptic made at Mar̄gha in 1264, 23; 30° (the real value in 1250 was 23; 32, 19°).
5. Maq̄la f̄ istikhr̄j ta ’d̄l alnah̄r wa sa ’at almashriq wa ͗ld̄͗ir min alfalak (“Treatise on Finding the Meridian, Ortive Amplitude, and Revolution of the Sphere”).
6. Muqaddam̄t tata’allaqu ḅ̄arak̄t alkaw̄kib (“Premises on the Motions of the Stars”).
7. Taṣ̣̄ alạ̣url̄b (“The Flattening of the Astrolabe”).
Editions of the Greek classics; they are called recensions (sing. taḥrīir).
8. Euclid’s Elements.
9. Apollonius’ Conics.
10. Theodosius’ Spherics.
11. Menelaus’ Spherics.
He also wrote more than six books on astrology and a memoir on chronology.
AlMaghrib̄’s writings on trigonometry contain original developments. For example, two proofs are given of the sine theory for rightangled spherical triangles, and one of them is different from those given by Ṇ̄ir alD̄n aḹs̄ this theorem is generalized for other triangles. He also worked in several other branches of trigonometry.
Ptolemy (A.D 150) used an ingenious method of interpolation in the calculation of chord 1°. This is of course approximately equivalent to chord 1°. The same method was used for sines in Islam. To find the exact value, one must solve a cubic equation. This was done later by the Persian astronomer alKāshī (d. 1429/1430), AlMaghribī, and before him Abu ’lWafā’ (940–997/998),tried to find the value of the sine of onethird of an arc. For that purpose Abu ’lWafā’ laid down a preliminary theorem that the differences of sines of arcs having the same origin and equal differences become smaller as the arcs become larger.
Using this preliminary theorem, alMaghribī calculated sin 1° in the following way (see Fig. 1):
VF = 1; 7, 30° and sin VF = FK = 1; 10, 40, 12, 34p
AV = 0; 45° and sin AV = AI = 0; 44, 8, 21, 8, 38^{p}.
The arc AF is divided into six equal parts and each part = 0; 3, 45° therefore,
arc DV + arc DH = 1° and sin HV(=1°) = HZ.
The perpendiculars AT, BY, and CK divide DT into three unequal parts: TY > YK > DK; TD/3 > HL; DQ + TD/3 (=1; 2, 49, 43, 36, 9^{p}) > HZ(=sin 1°). FM is divided into three unequal parts: MN > NS > SF; DQ + FM/3 (=1; 2, 49, 42, 50, 40, 40^{p}) NK = HZ (=sin 1°). Then he found sin 1° =1; 2, 49, 43, 24, 55p.
AlMaghribī calculated sin 1° by using another method of interpolation based on the ratio of arcs greater than the ratios of sines. He found sin 1° = 1; 2, 49, 42, 17, 15, 12p and said that the difference between two values of sines found by using different methods is 0; 0, 0, 0, 56p, which is correct to four places.
Using these methods, alMaghribī calculated the ratio of the circumference to its diameter (that is, π).
AC(=2AT)< are ABC < RF
sin AB(=3/4°) = AT = 0; 47, 7, 21, 7, 37p
ΔRFH ~ ΔAHC, RF/AC = BH/TH.
RF = 1; 34, 15, 11, 19, 25p
arc ABC = = 1; 34, 14, 16, 47, 19, 30p.
The circumference = 240. Arc AB = 6; 16, 59, 47, 18p, the diameter being 2p. The diameter being lp, the circumference 3; 8, 29, 53, 34, 39p < 3R + 1/7, since 1/7 = 0; 8, 34, 17, 8, 34, 17p.
AlMaghribī compared the latter and Archimedes’ value, 3R + 1/7 < the circumference < 3R + 10/71, found by computing the lengths of inscribed and circumscribed regular polygons of ninetysix sides. Half of the difference between 10/71 and 10/70 is equal to 0; 8, 30, 40p.
AlMaghribī determined two mean proportionals between two lines, that is, the duplication of the cube (the problem of Delos). In antiquity many solutions were produced for this problem. It was thought that in terms of solving this problem the mathematicians of Islam stood strangely apart from those of antiquity; but recently many examples have been discovered, thus altering this opinion. The following example of AlMaghribī’s is of interest in this respect. He finds two values (see Fig. 3):
AB and BC are given and AB > BC, and AB ∧ BC. AC are joined. Triangle ABC is circumscribed by a circle. The perpendicular DH is drawn so that DC must pass through point R.
HR = AB, RH/DH = BA/DH
AH = BR, RH/HD = DH/HA, Since angle D = 90°
BA/DH = DH/HA
But
RH/DH = RB(=HA)/BC
BA/DH = DH/HA = HA/BC.
BIBLIOGRAPHY
The following works should be consulted: A. Aaboe, “AlKāshī’s Iteration Method for Determination of sin 1° in Scripta mathematica, 20 (1954), 24–29; and Episodes From the Early History of Mathematics (New Haven, 1964), 120; C. Brockelmann, Geschichte des arabischen Literatur, I (Leiden, 1943), 626, and supp. I (Leiden, 1937), 868–869; P. Brunet and A. Mieli, Histoire des sciences d’antiquité (Paris, 1935), 333–415; H. Bürger and K. Kohl, “Zur Geschichte des Transversalenzatzes,” in Abhandlungen zur Geschichte des Naturwissenschaften und der Medizin, no. 7 (1924), 55–57, 67, 70, 71, 73–75, 89; Carra de Vaux, “Remaniement des sphériques de Théodose par lahia ibn Muhammed ibn Abi Schukr Almaghrabi Alandalusi,” in Journal asiatique, 17 (1891), 287–295; T. Heath, A History of Greek Mathematics, I (Oxford, 1921), 244–270; P. Luckey, “Der Lehrbrief über Kreis Umfang (arRisāla alMuhītīya) von Čamšid b. Mas’ūd alkāši,” Abhandlungen der Deutschen Akademie der Wissenschaften zu Berlin, Math.naturwiss. Kl., no. 5 (1950); and G. Sarton, Introduction to the History of Science, II, pt. 2 (Baltimore, 1931), 1015–1017.
H. Suter, Die Mathematiker und Astronomen der Araber und ihre Werke (Leipzig, 1900), 155; S. Tekeli, “Taqī alDin’s Work on Extracting the Chord 2° and sin 1°,” in Arastirma, 3 (1965), 123–131; and “The Works on the Duplication of the Cube in the Islamic World,” ibid., 4 (1966), 87–105; F. Woepcke, “Sur une mesure de la circonférence du cercle due anx astronomes arabes et fondée sur un calcul d’Aboul Wafa,” in Journal asiatique, 15 (1860), 281–320; and S. Zeki, Asari bakiye, I (Istanbul, 1913), 106–120.
S. Tekeli
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